LTIiRITE3 TRACi E£AAT STUDIS IA OF "u Z0RITES AND THL OtIGI by INSU4 , JR. WILIAM HAWT dT LT TECI A.B., Emory University 1948 Emory University M.S., 1949 SUBMITTED IN PA RTIA L FUISILLENT OF TME B4UIRi;IITS FOR TE DEOREE OF DOCTOR OF PHbO2OPHY at the MASSACHUS&TTS INSTITUTE OF TECHNOLOGY 1951 Signature of Author. ....... ......... Department of Geology November 27, Certified by . . . . . . . . . . . . 1951 . . * . . . . Thesis Supervisor Chairman, Departmental Committee on Graduate Studente . ACkXOSLDGMN TS I am especially grateful to the following individuals and organizations, without whose aid this investigation would not have been possible: Dr. i. H. Ahrens, who taught me the quantitative use of the optical spectrograph in the investigation of geological problems, and who has pointed out to me many of the most fruitful lines of research in this investigation. Dr. Ahrens suggested, for example, that we could prove by analysis that the K/Rb ratio in meteorites and common rocks was nearly constant, and that this fact would have important geochemical and petrological implications. The entire staff of the Geology Department at the Massachasetts Institute of Technology. Dr. H. i. Fairbairn, under whose guidance I acquired a large part of my knowledge of petrology. Dr. Harlow Shapley and the entire staff of Harvard College Observatory, who made it possible for me to acquire sufficient astronomical knowledge to write on the "origin of meteorites". Dr. C. L. Frondel of Harvard, who kindly supplied the meteorites for analysis from the Harvard MAuseum. Dr. H. Hess and Dr. G. L. Davis of the Carnegie Geophysical Laboratory, who supplied a collection of well-known altramafic rooks for analysis. Miss Geraldine Sallivan, who did several flame photometer analyses of meteorites for this investigation. The entire staff of the Geology Department at the gassachusette Institute of fechnology. My wife, Mary Pinson, who typed this thesis and helped in the proof-reading. Finanoial assistance for much of the work was given by the Division of Industrial Cooperation of the Institute. My thanks a given to all of the above. iii ABSTRACT This investigation was andertaken because there is a well-rOognized need for more abundant and more accurate knowledge of the trace element content of meteorites. Pre- vious investigators nave analyzed but few individual meteorites for trace elements, and for several of the trace elements, e.g., Rb, our knowledge of their abundances rests entirely on a single analysis of a composite sample. thermore, Fur- trace element analyses by different investigators are generaliq so widely divergent that it was suspected tnat many abandance values were in error. For the above reasons the spectrograms of twenty-one ohondrites (which comprise over 90% of silicate meteorites) were analyzed for 4, Rb, Ba, Sr, So, and Zr, All of these elements,with the possible exception of a small proportion of Zr, are confined to the silicate phase in meteorites. The speetra of all ohondrites investigated were remarkably similar. The trace elements determined were all constant in abundance within a factor of approximately 2, with two minor exceptions oat of a total of 125 analyses of chondrites. On the basis of the constancy of the trace elements in these randomly selected specimens, new abundance values are derived for several trace elements in chondrites, and argaments presented for their acceptance on the basis of the improved analytical techniques employed. The argument is presented that from the constancy of trace elements in meteorites we may infer that they all had a similar origin, in further support of the shattered planet hypothesis for the origin of meteorites. Approximately 400 analyses of trace elements in meteorites and rocks were made and the coomoohemical and geoohemical signifiance of the results are discussed. Three ele- ments, Rb, Sc, and Zr which had not been previoasly determined, were determined in a suite of rocks from the Skaergaard intrasive and shown to show enrichment or impoverishment according to accepted geochemical laws. At the saggestion of Dr. L. H. Ahrens, the % K/Rb ratio was determined in a large number of meteorites and rocks. These values plotted on a graph show the characteristic enrichment from basic to acidic rooks. is the proof that the ratio Of great importance %K/Rb is nearly constant in meteorites and common igneous rock types. This fact supports the belief that meteorites originated by processes of magmatio dirrerentiation known in terrestrial rocks. The graph de- picting the linear relationship or the ,bK/Rb ratio includes the analyses of both Ahrens and inson. Two chapters are devoted to the mineralogy and structure of meteorites. Those features which are significant in the study of origin are discussed. The final chapter, The Shattered Planet Hypothesis, is V an attempt to present in logical order the wealth of geological and astronomical facts which support this hypothesis. Inooneistenoies are few, and the lack of adeqante explanation of the oause of shattering does not detract from the hypoe thesis, Almost all evidence converges to the conclasion that meteorites originated within a planet, comparable to Earth or Mars in size. vi TK8]E OF GONTEWTS CRAPTR I. Introduction CRADTER II. Preparation, Spectrographic Techniques, . . . . . . . . . . . . . . . . . . . . . . lreparation of samples . . . . . . . . and Experiments . flame photometer chooks of K content . . .. . .. . .. . of meteorites Teehniqass for analysis of involatiles . Standards * . . . * * . * . . . . . s . . . . . . 8 . . . . 8 . 0 . 0 9 Zr standards for chondritic meteorites . * .* Ba, Sr, So in meteorites . . Ba, Sr, Se, Zr in Skaergaard suite and ultramafios . . . . 0 . . . . 9 . . . . . . . . . 9 . . . . . 0 9 . . . . . 0 10 . . 0 .5 10 . . . .0 10 Separation of the silicate phase * 0 . .0 11 Photometric measurements . .0 . . . .0 12 . . .0 14 . . .5 14 0 . 16 K, Rb in meteorites . . . K, Rb in Ontario diabaues. K, Rb in altramfices . . . * K, Rb in Skaergaard suite. K, Rb (and other alkalies) I tektites. . . . . * . . occentration for analysis o f CHAPTER III. Us . * K and Rb in Meteorites and Roaks Historical Oatline * . . . . Geohemistry of K and Rb . 0 . . . * 0 . , 00 Constancy of the ratio.,% K/Rb. * 0 17 vii Page . 21 ........... 25 . meteorites . X and Rb in K and R in diabasee . . X and Rb in Skaergaard rooks. . . .g ..... 25 . 28 . . . 29 . . . 30 . 46 Rb in altramsfios. .*.*. . . * The primitive K/Rb ratio Tetites OHAPTER IV. . . . , . Ba and Sr in Meteorites and Rocks Historioal review .. . . 46 ,......... Geoohemistry of ba and Sr. Sr and ba in meteorites CHAPTER V. . . . . ,. . . . . . . . . . . 49 . . . . . . . . . 50 Sr and Ba in Skaergaard saite. . . . . . . 53 Sr and Ba in ultramafio rooks. . . . . . . 58 So and Zr in Meteorites and Rocks. . . . . 69 Historioal review. . . . .. .*. * Geochemistry of scandim So in meteorites. . . . . . . So in Skaergaard rooks. . . . . . So in altramafio rooks. Geochemistry Zr in of hr. . . . . . . 70 . . . . . .. 71 . . . .. 72 ........ 74 .. . . . . . . . . . . .. hr in Skaergaard rooks . Zr in altramafic rocks . . . . . . . . . 0 . . 76 76 . . . . . 75 75 .. ..... * meteorites.. 69 85 QHAPE VI. Mineralogy . * C0APt iR VII. Struottres and Textures of Meteorites. . 106 . . . . . 106 . . .-- . . - Nature of ohondri (ohoadriAles) - - - - - viii Page . . *110 . . 112 . . ft 115 Gooling of the parent planet . . . . . 119 . . . .t 123 Origin of chondri. . . . . . . . .* Faults, fractures, and sliokensidee. asteorites. Veins in . . . . . , QEATER VIII. The Shattered Planet Hypothesis. Astronomical Astronomical facts and theories. * , ft 32$ Geological facts and theories. .. . .t 124 . .t 124 . ft 127 Association of meteors with omets and meteorites with asteroids Roohe's limit; a oause of shattering . Fragmental shapes. * . . . . . . . . 129 . . . 4 ft . 130 Geological The meteoritio seqence.. Geochemical and jetrologioal evidence.-- 132 Natare of pallasites . * ft . . .t . .t . . 137 Geochemical eqwilibria . . .t . . . .t .t 139 Widmaastatten figures . . . .t . .t . . 144 . .t ft . . ft .t . 146 . .t .. .t . f .t 148 . .t . . .t ft ft . . . .t . ft ft .t , 9 . ft ft . 153 . Ages of meteorites Olastio struatares . . GOAlER I.4 Conclustons. . .*. C0APT1R X. Suggested Research . Biographical Bibliography Appendix . . Data .t .0 ft . . ft . . . . . . . . . . . . . . ft . ft ft . . ft . . . 0 , . 149 151 ft . . ft ft .t . . . . 164 . . , . . . . . . . 162 im LIST OF TABS ago TAB.E I. K and ib in Meteori tes and Rocks TABA II, ha and Sr in Meteorites and hooks. . . . . TAB±4 III, So and Zr in Meteorites and Hooks. . . . . *. . . . 40 60 8 45W0? IGuRSs Figure 1. l X/b in Common Rooks and steoritee . . . . K/Rhb in Skaergaard Intrusive Rooks 24 .. . 19 26 . 3. Variations of K and Rb In Skaergaard Rooks. 4. * 27 . 4O in Metal-free Homestead Meteorite by Addition Method . . . . . . . . . . . 34 . 35 .... .# MeteoriteS. Metal-free 5.$KOO in . Working CMroe 6. # Rb 0 in Metal-free Homestead Meteorite by Method. Ad ition 7. %3b2 0 . 10. % K in Diabases . . . . . . . 36 ... * . , . . . . *. . . . . * . . . .4 , * . . . . 37 38 . 39 . Variations of Ba and Sr in Skaergaard * . Intrasive 0 . 11a. . in Metal-free Meteorites, Working Carve. 8. % Eb in Diabase. 9. . . . . . . . . . . . . 55 .# . %ba in Metal-free Homestead Meteorite by . * 61 a *. .. 62 .. 63 14. % sr in staergaard fooks and Ultramafios . . .. 64 lb. Variations of So and Zr in Skaergaard Addition Method, . . 12, Method . . . Intrasive . . . . .. . . . . . . . .. . , . . . . . . . . . . . . . . ., , . . . . . . . . . . . . . . f So in Metal-free Homestead Meteorite by Addition Method. . 17., * % Ba and Sr in Metal-free Meteorites, Working Carves.. 16. . .. % Sr in Metal-free aomestead Meteorite by Addition 13. . . . . . . . . . * . . . 7? . So in tetal-free Meteorites, wiorking Curve. . . . . . . . . . . . . . . . . . 78 .. 18. 5 So in Skaergaard Gabbros, Working Carve . 79 19. % So In Skaergaard Granophyres and Tektites . . so . . GHAPTER I INTRODUTION The purpose of this investigation has been threefold: 1. To establish more accurate abundanoe values for the elements K, Rb, ba, Sr, Sc, and Zr in ohondritio meteorites. * To relate and compare these abandanoes with terres- trial basic and altrabasic rocks. 3. To review the geological and astronomical litera- ture on meteorites and to present in logical order an argumont for the origin of meteorites. A review of the literature led to the conclusion that the abundance values for traoe elements in meteorites rest indeed on scant analytical evidence. For example, the abundance value for meteoritic Rb is due entirely to its determination by the Noddaoks in a gomposite sample. Ba, Sr, Zr, and So have been determined in but a very few meteorites, and results nave been so erratio that averages would seem likely to be in error. Recent analyses for K in ahondritio meteorites indicate tnat many of the older analyses by wet chemical methods were in large error, as demonstrated reoently by W. danl. The same criticism could be applied for all bat a very few traos elements. Harrison brown recently found the aban- dance value for Re as determined by the Noddacks to be in error by a factor of b. No reflection is intended on the works of earlier analysts, for their analyses were necessarily of a reconnaissance nature. They have been extremely useful, and in most cases the order of magnitude was correct. However, new improved methods of mioro-chemioal analysis make new determinations of certain elements feasible. The need for more accurate determinations to place cosmic abundance values on a better statistical basis, and especially the need of a knowledge of the cosmic ratios of the elementsis wellrecognized by physicists and cosmologists. The most striking observation to the writer is the near constancy of composition in trace elements of chondritic meteorites, as shown by their~spotra. Finally, the writer has attempted to present in logical order an argument for the "shattered planet hypothesis" as the origin of meteorites. that meteorites originated in a planet -of Mrth-sre (or smaller), which was subsequently shattered afttn cooling, is suggested by a wealth of geologloal an'P astronomical observations. of this theory seem few. The inconsistencies 0. Bauer of Harvard College Ob- servatory (1949) has written one such excellent argament. It is noped that the writer, as a geologist, has added some strength to this nypothesis. CHAPTER II PBARATION SPEOTROGRAPUIO ISD ZXPSM.ISTS TE Preparation of aMLes ]Every effort shoald be made to prevent contamination in a trace element analysis. in mind, With this the writer made wide use of the life-long experience of H. S. Washington, as recorded in his book on silioate analysis, and followed Washington's advice on the principles of preparation of silicate samples for analysis. The rook samples were each selected on the basis of their homogeneity of mineral content; that is, sufficiently large samples were selected wherever possible to ensure that a representative portion was msed for aroing. Five to ten pound specimens were used for the Ontario diabases. Bach was first broken in a screw vice and the fragments granalated in a jaw craher. This portion was coned and quartered, followed by further pulverization in a diamond mortar, and suocessively quartered until a twelve-gram sample was obtained. This portion was finely palverized in a mechanical agate mortar and pestle, and a 3 gram sample separated by ooning and quartering. This portion was used in the spectro- grapado analyses, and is considered highly representative of tne composition of the original rook. Similar procedures were followed for the altramafic rocs, except that the jaw-crasher stage was omitted, for only smaller samples (approximately available. t to * pound) were However, because all the specimens were homogen- eous in mineral oontent, as shown by thin section or hand lens stady, these speoimens were considered adequate in size. The seven specimens from the Skaergaard saite of rooks averaged only 10-20 grams each. For this reason, if the analytical results of this investigation vary from those of L. R. Wager and R. L. Mitchell (1943), it is probably because of the small samples employed, for Wager and Mitchell However, for the used larger, more representative samples. purpose of tais investigation, the samples show the trend of enrichment for the elemants K, Rb, l5a, and Zr from base to top of tao intrusive, a similar deerease in So content, and a oonstanoy of the ratio K/Rb. Also, analytical agreement with Wager and Mitohell is in most cases close. The magnetic separation of the metallic phase from chondritic meteorites is extremely tedious. The meteorite samples, weighing from b to 100 grams each, were pulverized in a new diamond mortar. The fine portion was sifted through a fine-meshed silk bolting cloth, a fresh cloth being used for each meteorite. The coarse metal grains were extracted by magnet and hand-picking, while the remaining coarse fragments were again pulverized and sifted. This process was re- peated until the meteorites were reduced to coarse metallic grains and a finely palverized separate portion of silicates and salfides (the non-magnetic portion) was obtained. However, considerable metal remained in the palverized portion. Previous investigators have removed the metal with a magne tic comb. meteorite, All workers report spending hous on each The tenacity with waich metallic particles remain in the mixture is remarkable, The writer employed a variation in tAis procedure -- bat also spent hoars in each separation. The palverized mixture was plaseA in a glass sample jar, waich was rotated by hand while a powerful hand magnet was held against the glass. A piece of paper was placed between magnet and glass, so that when the metallio particles were drawn out the mouth of the sample bottle they would not adhere to the magnet, Unfortunately, some olivine is uagneti- cally inoladed, probably due to inclmsion of Ni-Fe particles, even in finely pulverized grains. However, these silicate particles are less strongly attracted than the metallic partie ales, so taat separation may be made by spreading the attracted portion on a sheet of paper, rolling the particles about with the fingers through a paper sheet to separate them, and then passing the magnet over at a sufficient distance above the particles to attract only the more ta metal particles. agnetic ones -- If this detailed description seems lengthy, it is inserted here only in the hope that it will be of use to futare workers with meteorites in this tedious process. Finally, great oars was taken throaghout the investigation to prevent contamination with radioactive materials, for these meteorite samples are to be analysed for radioactive content. of meteorites; flame photometer cheeks of X content n '""M - -_ - 1.00a M0 60 '"W1 Miss Geraldine Sallivan, Research Assistant at M.I.T., made flame photometer analyses of three meteorites for content of K, and, incidantally, Aa. The meteorites were prepared for analysis by the writer by dissolving one gram samples in HF (plus 5% 12 304 ), evaporating to dryness and repeating. Description of the technique is given by L. H. Ahrens (1951). The residue (Si removed as SiUt) was dissolved in 250 ml, aliquots of 2% 101. The flame photometer analyses were made by Miss Sallivan. Resalts in all cases, as shown in a table of Chapter II, agree excellently with spectrographic analyses and serve to ennance the validity of both analytical procedares. techniques for analysi of involatiles: The elements Sr, Da, So, and Zr present a special problem in spectrographic analysis in that these elements, especially So and Zr, are among the most involatile. In order to enhance the sensiti- vity or these elements, the rooks and meteorites were mixed with equal portions of pare electrode carbon powder. This powder was checked qalitatively and found free of impurities of the elements sought. Palladium, as palladium chloride, was added as internal standard. However, the intensity of the sensitive Pd line sought did not seem to be of sufficient constancy to warrant its ase. Equally precise, and more trustworthy re- salts were obtained without use of an internal standard for the four elements soaght. However, in future investigations, teonniques using internal standard will be developed for meteorites. Analysis was fade with the Wadsworth grating spectrograph, whieh has been adequately described in other publicstions (Denen, 1949). Seven steps, each in the intensity ratio of 2.0, were recorded, tsing a rotating stop sector. Pare carbon electrodes, of dimensions 3/16", 1/8", 1/4" were employed. The cylindrical cavity in eaoh electrode was loaded with from sixty to seventy ug, of material. Anode excitation was used, and arcing time averaged 3'10" for the meteorites, and slightly less than 3 minutes for the less refractory rook samples. All arcing was to completion, for So and Zr are among the last materials to be volatalized. The plate holder was centered at 3800 A, and loaded with 3 plates (Eastman 103-0). The ninety plates of this inspection for involatile elements were developed in batohes of fifteen, tas comprising six developings. All plates were saved for developing until all arcing was complete, so that constancy of developing ditions would be better assured, This is, of course, of sa- preme importance in qaantative spectrographio work. veloper (D-19, Qon- The de- Eastman) was sufficiently freshened for each lot of plates developed to insure uniformity. was 4.b minutes, at 2000. Developing time The plates were immersed at 1900, and being somewhat warmer than the developing solution, the temperature rose to nearly 210C at toe end of 4.5 minutes. Standards: Several different standards were necessary, because of the diversity of materials arced. Zr standards for ehondritic meteorites: The addition method described by L. H. Ahrens (1950) was employed. This mtnod htes tao advantage of using the material analyzed as base (matrix material), an important consideration in analysis of meteorites, beoause of the difficulty of producing a syatinetic base that would simulate stony meteorites in arcing characteristics. The Homestead meteorite, with tatal magnet- ioally extracted and FeS onverted to Fe20% by heating, was used as base to which successive quantities of the Standard Granite G-1 were added, in the ratio of 9/1, 4/1, 2/1, 1/1 of meteorite to granite. Intensity of the line Zr 5391.975 was plotted against tAe percentage zirconium added, as G-I. Analyses were in triplicate for each point. beoaaae of the spread of the points a considerable leeway in fixing the line slope and its point of intersection with the percentage axis * Fairoairn, H. W., U.S.G.S. Special Bull., 1951. was encountered. However, after the best line possible was drawn, this value ror percentage zirconium in the Romestead meteorite was compared with the value obtained by comparing it with the known zirconium content of the standard granite G-1, for wnioh a single working curve was construoted. The two values than obtained, being very nearly equal, were averaged to give the value Zr in the samples of Homestead analyzed. Ba, an r,aand So in Meteorites: For the elements Sr, Ba, So the addition method was employed, as above. W-1 was added in the ratio 99/1, 49/1, 19/1, 9/1, and the results were compared with single point working curves of W-1, and results averaged. Thas the Homestead meteorite was found to contain 0.0012% Sr, 0.0011% Ba, and 0.00124 So. (V. M. Goldsohmidt found 0.001* So in Homestead). ", sr, so, Zt iA gegaard ,Suite and Ultramsfica; The values -for, the be four elements were obtained from single point working carves of W-1 and G-1. 4 Rb in Meteorites, The addition method was employed, in which K and Rb were added as G-1, the ratio of Homestead to -1 being 99/1, 49/1, 19/1, 9/1 for sucoessive arcing:. K, Rb in Ontario diabases: Values for the thirty dia- bases analyzed were obtained from two point working curves, employing G-A and W-l. K, Rb in Ultramafios: Analysis values were obtained from single point working curves of W-1. K, Rb in Skaergaard Saite: Comparison was made with two point working curves of W-1 and G-1. KRb In Tektites: All spectra were compared with spec- tra of G-1. Note: All analyses for K and Rb were made with the 111- ger prism spectrograph in the Cabot Spectrographic Laboratory. Eastman I-L plates were used; developing in D-19 at 2000 for 4.b minates. All meteorites were sintered before arcing to convert iron sulfides to oxides. Sintering was necessary to insure smooth burning and prevent loss of sample by spattering. Seven steps of a rotating step sector were used. Slit height was 10.5 mm.; allt width, 0.06 mm. Experiments Concentration, toR analysis of Oeeaat Considerable effort was made to concentrate Cs from stony meteorites. Cs was not found in tne six specimens concentrated (3 of Homestead; 5 of Hayes Center). It is concluded that the aban- danse of Go In stony meteorites is less than 0.00001%. The concentration method (Ahrens, solution of the meteorite (1 - 1951) employed was 2 grams) In hydrofluorio and perchlorie acid; prolonged heating at 45000 in furnace, in which all elements bat alkalies are converted to oxides; solation of alkali chlorides in various organic agents in which they exhibit different solubilities; arcing the portion enriohed in K, Rb, Cs. This method is fully described by F. B. - *~ an ~b~n 11 Whiting (1951). However, L. H. Ahrens (personal communiaic. tion) has sugg3ested a method of further enriching Rb and Ga. Worn is now in progress on this suggestion. saration of the silicate phase of ohondritio meteorites; Mach work has been done by the writer and previous workers (Prior, 1919) on this problem. Chondritio meteorites are com- posed of a mixture of three phases, metallio, sulfide, and silioate. So intimate is this mixture that it defies methan- ical separation techniques. in which Hgal 3 (JH3)2 Prior (1919) suggested a technique was used as a dissolving agent for the retal and sulfide phases (stronger agents are not suitable, for they dissolve olivine). This method was attempted. The reagent reacted with the pulverized meteorite for 96 hours in an inert, nitrogen atmosphere. At the end of this period, however, considerable metal was still andissolved, as shown under a microscope. Also, it appeared that the olivine had been attacked. The experiment was repeated three times, asing HgOl 2 on one ocaseion with similar unsatisfactory results. This technique worked for synthetic mixtures of iron filings and pulverized diabase, but not for ohondritio meteorites. The resulting material could not be used for pure silicate phase analysis for trace elements. For future trace element analyses of the silicate phase. of meteorites and the analysis of individual meteoritic miner- 12 al.s, the writer suggests that mauch effort would be saved utilizing materials from actondritic stony meteorites, in many of which mechanical separation techniques can be *aploLy. However, detailed traoe element studies in meteorite minerals is greatly needed, and further investigations should be made. .4Wahl (1901) has suggested methods used by metal- largists in separating silicates from cast iron for analysie whioh will be tested on meteorites by the writer. This reference did not come to the writer's attention in time tor tWie investigation. The various working earves for the different elements are incladed in subsequent chapters which are pertinent to the particular element. Photometric measurements: Photometric determinations of the elements K, Rb, Ba, Sr, and So were made with a Hilger microdensitometer. bThe responses of a photoelectric cell and galvanometer were converted into intensities by means of a calibration ourve. All analyses were in triplicate except those for the Skaergaard suite of rocks, which were in quadraplicate. Zir- coniam was determined visually. The analysis lines of the elements sought were selected on the basis of their intensities and lack of interference of background and interfering lines. Great care was taken throughout this investigation to 13 prevent contamination. The carbon eleotrodes used were arced as blanka and found to be free of impurities of the elements sought. no chemical agents or adulteranto were added to the standards or unknowns. CHAPTER III X AND Rb IN MTWEORITS AND ROCKS !istorical outline: Potassium has almost always been determined in the analyses of siliente meteorites. Until quite recently K was determined by wet chemical methods. At present it seems that K,'as well as Na, can most easily and accarately be determined by either flame photometer or spectrographic methods. Farringtoa (1911) oompiled a catalog in which are listed selected analyses of stony meteorites. The norma- tive mineralogic oompositioas for all the meteorites were calcalated and the meteorites classified. Most of the me- teorites analysed for trace elements by the present writer are included in Farrington's catalog. Detailed descriptions will not be repeated here, for this catalog may be easily referred to by anyone interested in the major element analyses of these meteorites. In the appendix of this thesis is in- cluaed a brief mineralogic description of the meteorites analysed in this thesis, based both on Farrington's catalog and the writer's stady of thin sections of his specimens. W. Wahl (1950) has recently proved that in a number of old analyses K and Na were wrongly determined by a large factor. He concluded that any analysis showing abnormally high K or Na percentages should be regarded with suspiolon, and that these meteorites should be reanalyzed before being incladed in meteoriti* or cosmic abandancet compilations of the elemnts. The restlts of the writer in the analyses of twenty-one ohondrites oos&ra this conolasion of 4ahl. Even casual visaal inspection of the spectra of these meteorites reveals most strikindl their near identity, both in composition and abundance of the elements. Although twenty-one specimens are admittedly a small nAmber o" which to base final oonelusions, it is most remarkable that these randomly selected spooimens should be so alike in composition. The abundaao valaes for & in the current literature are based on the compilations of G. P. Merrill (1950) and the Noddaeks (1930). Recalolations were made by V. M. Goldsohmidt (1938) and by H. Brown and 0. Patterson (1949) of seleoted analyes. Rankama and Sahama (19bo), viewing tae literature, derive the valuae 0.20 silicate phase of meteorites. Ib after re- % K for the Assuming an average value of tree-metal phase, hankama and Sahame's valae soald be cfia. 0.17% for silicate meteorites. Assuming that I0A of silicate meteoritee are aohondritic, and very low in K ountent, as the writer's investigation has indioated, the value would be redaoed to cir. 0.lb% in silicate meteorites. the abundance of K and Rb in terrestrial rooks and minerals has been reviewed exhaustit#l7 by Rankama and Saname (l90)* Solar and stellar abundanoes of D. g. Hans.el , K. 0. Wright, and A Unsold have been tabulated by H. G. UrOy (1951). Rabidiam has been detected in the San t s atmosphere. The abundance data for Rb in meteorites is Indeed scanty, and are based almost entirely on the analyses of the Noddaoks (19130). These analyses were made by optioal spectrographic methods, and the abundance value of 0.00045% Rb in the silk. atse phase of meteorites is based on the analysis of a composite sample, composed of forty-two separate meteorites. The ned for individual analyses for Rb in meteorites is obvious. To the writer's knowledge, these twentywone ana- lyses represent the first individual analyses for Rb. This investigation on twenty-one ohondrites indicates that both K and Rb are constant within a factor of approximately 2. G11heoft X and Rb: Rankama and Sahama have ex- cellently reviewed the literature and diseassed the geohemistry of the alkali elements. Here only a brief review, ger- mane to this thesis, will be given for K and Rb. The elements K and Rb are known to sabstitute for one another in the crystal lattices of minerals. This eabstitmoo tion is possible because of the close similarity in chemical properties of these elements, dae to their identity of charge and their similarity of sizes. The ionio radii are given below. K+ r45 A Rb+ 1#49 A 17 The bulk of K and Rb in the igneous rocks is found in the potash feldapars, and to a lesser extent in the potash micas. minor amounts of K and Rb are contained in the Teld- spathoids, alkali pyroxenes, and alkali amphiboles. Both potash feldspars and micas are late crystallates during magmatic differentiation. For this reason these elements are concentrated in rocks of late crystallization, e.g., However, potash micas, especially syonites and granites. biotite, are common constituents of certain altrabasio, basic, and acidic rocks. Some ultramafic rocks, such as kimberlite and mica peridotites, contain large percentages of K and Rb, comparable to granite. For this reason, as pointed out to the writer in conversation by Professor G. Kennedy of Harvard University, abundance valaes of the elements (e.g., K and Rb) in altrabasic rooks will depend largely on our knowledge of the actual percentages of mica-bearing altramafic rooks in the Earth's crust. However, except in abnormally mioa-rich rooks of a class, the K and Rb oontent increases markedly from basic to acidio roccs, and, as shown in this investigation, the ratio K/Rb is remarkably constant, as demonstrated in Figure 1. GOnstancy of fth Rao fK/Rg On a basis of geochem- ical theory, it was saggested to the writer by Dr. L. H. Ahrens that X and Rb should be found in nearly constant ratio in all common rocks and meteorites that formed by magmatic proOesses. Dr. Ahrens had already detcrmined L and Rb in over two hundred granites, diabases, and basalts, and found the ratio to be remarkably constant and to aver. age approximately 80. At Als suggestion, the writer deter- mined X andi Rb in twenty-one chondritic meteorites and sevoral aisoellaneous types, and in several gabbros, twentynine diabases, and some altranafics, The results of these analyses are plotted in Figure 1, as £X against % Rb. Almost all of the points fall near a straignt line, and this line closely approximates 450 in slope. The points include the analyses of the writer and those of Dr. Ahrens a4 his assistants at M.IIT. It should be pointed oat that numerous other analyses for 9 and Rb have beetn made by Dr. Ahrens which have not been plotted on tais graph (for the sake of clarity in drafting), but these values invariably lie close to the inoluded points. If ins oluded they would statistically improve the relationship. Any anomalous results (such as the one point which is isolated) have been included. rare, and all analyses , Anomalous results were indeed fall close to the value100 for the /rb ratio, This straight line relationship is significant in that it demonstrates that K and Rb readily substitute for one anotner in common igneous rooks and meteorites. Furthermore, tne enrichment in X and Rb from basic to acidic rocks is Fi~are 1. '1,f' 'H' 1: If 74 I 1 - It if K217+ It:, g 1441 T, I ~p~:: ~4It+4~~ li I..J~i'{ jr 4 41. 4i It 7. tg -- T 11J = .U: 4, 14 ;1 TR4*tIM - ttl rH~v 1: *1± ~~ ±i17±tii Itititi-LiJI r t j-Tp- fl~- :17 .. L 71 -ii]lifITftJiHllltiW-UAI rTr :a4uH41glimja m rT "-H-+-i 1 TZORIT'S ljpffffm iill 11111111 H-H-H-;441i v:HH 111#4+4W444+4 H t44+4i.444M4 I'M mm tr VI,~ demonstrated. A straight line drawn through the points in Figure 1 will be slightly lose than 400. This would indicate a slight enrichment of fib over K from basic to aoidio rooks, i.e., from meteorites to granites, However, the deviation of the line from 450 is but slight, and could possibly be due to small analytical error, as for example the use of several different standards in determining K and Rb in the different rook types, For this reason, only casual mention is made of this possible relationship. However, on theoretical grounds Rbt should be slightly enrifal over K in more acidic rooks. At the higher temper- attres at waich meteorites and basie rooks orystallised, the Rb+ ions would possess higher thermal energies than the X+ ions, and are less likely to be captured in existing crystal lattices, with resultant slight enrichment in the residual magmatic liquid, The larger Qs+ ion is known to be greatly enr Lofted :akSen rooks and even to rorm cesium minerals. Rb is not taown to form rubidium minerals. Also, numerous analyses of K and Rb in late small volame residual rooks by Dr. Ahrens have shown that Rb is significantly enriched over K. These rooks are not included in the graph booause they are not common rook types. ohondrites are incladed. For a similar reason, only the 21 The resalts of this investigation seem to the writer to be particularly significant. The K/Rb ratio in chondrites is essentially the same as in terrestrial igneous rocks. Were this ratio different in meteorites, it.would be reasonable to assert that ohoadrites formed by some other process than cooling of a silicate melt. As previously pointed out, the sole determination of Rb in silicate meteorites is based on the analysis of a composits sample by the Noddaoks, and is given as 0.00045%. The currently accepted valaes for K in silicate meteorites is approximately 0.2. Thus the ratio is indicated to be great- er than 400, larger by a factor of 4 than the ratio in common terrestrial igneous rooks. The analyses of the writer have saggested that the 4Rb ratio in chondrites (and silicate meteorites in general) is approximatelyD00, in agreement with terrestrial rooks. Al- tnough systematic error may exist in the writer's analyses for the aotaal percentages of K and Rb in meteorites, there is good reason to believe that the ratios of these elements is correct, for the intensities of the Rb and K lines measured in the ohondrites are nearly constant. is approximately 3, as it The ratio 0 0 is in common igneous rooks. X end Rb in Meteorites: The alkali metals, inclading K and Rb, are unknown in the metal-salfide phases of meteorites. As defined by V. M. Goldschmidt, they are specifically 22 lithophile elements. Potassiam and rubidium were determined in twenty-one cnondrites, two carbonaceous meteorit-es, olivine from a pallasite, one oladnite (composed almost entirely of bronsite) and in three tektites. The determinations were in tripli- cate. Becaase of their common occurrence, investigations in this thesis are confined chiefly to the chondrites. For a similar reazoa, deter4nations of I and Rb are confined to the most common rock types, which are representative of the balk of material in the Earth's crust. The alkali elements Li, Na, and X all may be deteoted in meteoritic olivine and pyroxene. It is easpected that Rb and possibly Gs are likewise present as minute traces. The elements Li, Na, and X were deteoted in all the dunites, serpentisttes, and pyroxenites analysed, as traces. However, in all these specimens it is suspeeted that Na and K are present in mineral structures other than olivine or pyroxene perhaps in mioas. In meteoritio olivine, beeause of the ani- versal occurrence etinlausions of other mineral grains and glass within the crystal, it is not known whether these elements are incorporated in the olivtine.orystal lattice. suspected that they are not. There is a tendeacy for Li to proxy for Xg It is and Fe becaase of similarity of ionic sites, but prozying ooaurs significantly only in sI0essively lower temperature minerals, rather than in Aidh temperature olivine and pyroxenes. Olivia, from a pallasite specimea (locality unknown) was analyzed. The olivine fragments were knooked loose with a ammer ad te aaterial ortbshed,and freelof aetattic particles by a magnet. Ties analysis demonstrates tnat K and hb do not readily abstitute. Likewise, the Johnstown, Golorado, chladnite was analyzed to demonstrate that the alkali elements do not readily enter the crystal structures of the meteoritic enatatitehypersthene series, Aikali feldspars are unknown In silicate meteorites, except by norm analyses. S The elements Ua, , Al, Si, and 0 are all present, bat thin section studies fail to reveal alkali feldspar minerals. Meteoritic olivine and pyroxenes do not contain K, nor is it in the metallic or salfide phass. It is conoladed that K is contained in the interstitial glass, which is a common and usually abundant constitaent of anondritio meteorites. Micas and amphiboles are unknown in meteorites, due to the complete absence of water, or the hydroxyl ion, which is essential to tna ionic structares of these minerals. Either Cl" or F- can proxy for 05" in these mineral stractures. fluorine has never been detected in meteorites, although it 24 has been caref4ly searched for, as will be Later reviewed in the oaapter on mineralogj. Chlorine is present in large quantities in metallic meteorites, and has been reported for stones. keoaase of its greater affinity for iron, it occurs as tAe rerroas chloride mineral, lawrenaite. The average 4 content of the twenty-one chondrites anas lyzed was found to be 0.084%. An average of 0.00085% Eb was found for the ohondrites. The aaalytical results for & were oecked by the flame photometer (G. Sallivan and W. Pinson, analysts) and are given in the following table. -A was determined incidentally. The writer's results are smal- ler by a zactor of approximately 2 than analgsea cartently appsaring in the literature by good analytical chemists; for example, those of t. Weahl. The writer does not wish to cast any aspersion on each analysea in any way. The present re- sults are acepted here as tentatively oorrect, because of the good agreement of flame photometer results with spectrograph- Ic resalts. Nonetheless, regardless of whether or not the actual percentages are correct, the relative intensities of tne i and Rb lines measared do not seem to be in error, and are in the ratio of intensities of approximately 3:1. wise, the Like- £/Rb is elose to 100 on the average, and would not seem to be in error. The table comparing flame photometer results with spectrographic results appears on the following page. dKV %iK Na Sample ae& Sairide Flm Photo-meer iate & loatf SulieSlfide lT TIi"Thoto tro lie~ir & ' Spec Gah Homestead 0.79 0.01 0.11 Haye's Center 0.68 0.096 0.07 Aernoive 0.72 0.103 0.11 K and Rb La Diabases; Twenty-nine diabases from the fippiesing and Matachewan areas of Ontario were analyzed for K and Rb. These rooks and numerous others are currently being investigated in the geology department of M.I.T. by L. H. Ahrens, H. W. Fairbairn, and assistants, for other trace elenmats. The average K content was found by the writer to be 0.94*: the Rb oontent is 0.014% Rb. ratio % K/Rb is approximately 70:1. Thas the Plots of these analyses are recorded in Figure 1. Indiviaal analyses for K and Rb are given in Table I, and were determined spectroscopically by the writer. and Rb in te Sje5ard Rocks: Seven specimens rep- resentative of the Skaergaard intrasive from base to top were analyzed for K and Rb. The petrology and mineralogy, with especial reference to trace element distributions, are described in several publications by L. R. vager and W. A. Deer (1939), and L. R. Wager and H. L. Mitchell (1943, 1951). Rubidiam had not been previously determined in six of the specimens. The writer's determinations of X were in reason- Figure 2. .--.. I . ........ --. X W leP ~ ~g~a/1 . .~ F '-4 - - lt[/r~ I ~1- F %7. in II 8 9 SkaeraaWr,' iorek 9it/e 46 6 7 8 9 10 0-OV Fi~re 4~ 11 I It I Id M ~- 4 v~4 /A'7Tdc?4~5/ a-24% k MitIevae/ & AliI 4-4 Ao6 7 1 4 rot /go?' /S05 8"9 sore I able agreement with those of Wager and Mitchell. Figure 2 is a plot of the writer's determination of K and Rb showing variation in composition from base to top of the intntsive. The analyses of Wager and Mitchell are plotted for comparison. The sympathetic increase in both K and Rb from base to top of the intrasive are illustrated. Figure 3 is a plot of %K against % Rb in the Skaer- gaard intrasive and demonstrates the straight line relations ship of K and Rb oontent from basic to acidio rooks: again, it is not known whether the deviation from 450 slope reproseats an enrichment of Rb over K, or is due to analytic error. In these analyses W-1, the standard diabase, was used in analysing the gabbros, while G-A, the standard granite, was used for acidic rooks. K nd Rb in, 3ltramafo Rooks Potassimm and rabidium are impoverished in most altramafic rooks, except those that are rich in miea, Of the twelve altramafics analysed, only the diamond-bearing Arkansas peridotite and kimberlite *ontained significant K and Rb. All the danites, serpentines, peridotites, and pyroxenites showed negligible quantities of K ( 0.05%), while Rb was not detected. The K and Rb in the Arkansas peridotite and kimberlite are present almost entirely in biotite. The ratio % K/Rb is smaller in these two specimens than in common potash 29 feldspar-rich rocks, demonstrating that Rb is enriched over K in the biotite stractare, as compared to feldspar strao. tares. A specimen of anorthosite contained 0.05% K and 0.0005% Rb, with the sonsequent ratio.% K/Rb of 100:1. To the writer's knowledge, this is the ffrst determination of the K/Rb ratio in anorthosite. Both K and Rb possess radioactive isotopes, viz. K40 and RbOT. Oalaulations based on the half-lives of these two isotopes and their present relative abundanoes dtow that the change in ratio of K/Rb throughout geologic time has been negligible. Data for making these calcalations is based on the constants used by Sawyer and Wiedenbeck (1950) and Ahrene and Gorfinkle (1950). The caloalations are as follows for K40, Half life of 0 = 1.27 x 109 years Decay oonstant, k, = 5.47 x Relative abundance K 9: 00o(years)r K0 iel = 93.8: 0.012: 6.61 KeS= Present abundanes of K 0 60 = Initial abundance of X40, aseaming geologic time, t, to be 3 x 10P years. 40 40 -kt 40 5.17 30 Similarly for Rb8 7 ; Half life of Rb87 = 5.9 x 1010 Decay constant, k = 1.18 x 10'11 Relative abunda~oe, RbSZ - = 7.28: 27.2 b8 5 ; Rb8 7 1.036 Thus it is readily seen that- the primitive ratio K/Rb was almost identical with the present ratio. Assuming geologio time (or cosmio time) to be twice or three times as great as 3 x 109 years would make no significant differenoes in present and initial ratios. The constanoy of the K/Rb abundance ratio is due to the very small isotopio abundance of t0 , making the changes in abundanoe of 40 insigni- ficant with respect to the other potassium isotopes, and to the long ha lf-life of Rb8 7 , making the changes in abundance of Rba8 insignificant in geologic time. Incidental to this observation is the heat production by radioactive disintegration throughout geologic and cosmic time due to K40 and Rb87 . Three billion years ago the heat prodaction from K4 0 , beoaase of its greater abandance, was approximately five times that at present. Because of the long half-life of Rb8 7 , heat production from this isotope was almost exactly the same as at present (greater by a factor of 1.036). Teztites: The origin of tektites is unknown. Beoaase of 31 their peculiar occurrence and geographical concentration in certain areas and their peculiar compositions they have been classed as meteorites by most investigators. The purpose of this investigation is not to establish either the meteoritio or terrestrial origin of tektites. However, trace element studies indicate that their compositions are extremely unlike terrestrial rocks and more nearly resemble meteorites in trace element composition. The anomalies are briefly listed below, based on visual comparison of the spectra of tektites with those of common Earth rooks, eg., standard granite and standard diabase, and on the literature. 1. Average 8i02 content Is 77%, being more acidio than any granites and comparable only to some alaminoas shale in gross composition. 2. Al content (approximately 11%) is higher in tektites than in most granites and shales or other common terrestrial rooks. 5,. Na( % X, opposite to the relationship of these two elements in terrestrial igneous rooks, but similar to average granite in ratio, 4*. % S comparable to that of meteorites, diatases, and altramafio rooks, and distinctly higher than for terrestrial siliceous roocs, such as granites and shales. 5.% Zr comparable to that of granite. 6. % Sr> % Ba, in contradistinction to the relationship 32 of Ba to Sr in acidic terrestrial rooks, in which Ba is always greatly enriched. Ratio & Ba/Sr found to be 42 for aver- age Of three tektites. Ratio % Ba/Sr > 8 in granites. 7. Ni content markedly higher than in highly siliceoas terrestrial rooks, such as granites and shales. 8. The content of iS, Rb, and o is comparable to that of granites, as shown in the following table, based on the analyses of three tektites. Tektites Analyis of Linok S0yI Tektites Pinson Nap0 3.b8 1.79 0.45 K2 0 Li2 0 5.42 0.00045 2.71 2.48 Rb2 O 0*061 0.02 ---- 0.00025 0.00025 e--- .a0 0.0005 a On the basis of the dissimilarities between the chemical compositions of tektites and terrestrial rooks, it is diffioult to support the theory that they were derived (by lightning striking and fasing rooks, or otherwise) from terrestrial roeks, They do not resemble even remotely any known volcanic glasses or other terrestrial rooks. The origin of tektites will probably never be established as meteoritic uAntil one is seen to fall as a meteorite, but we *Link, Gottlob, Aufban des £rdballs, Rede gehalten sur Feier des akademisohen 2i4ThVerTTelr*inMgam 21. June, 1924, Jena. 33 may conolade that they are dissimilar to all terrestrial rooks in so many ways that their terrestrial origin seems doubtfal. ,- . . 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I -1 I - - r 7 ' -I I-± -:_"_: I - ' +___ F - - - I- , , - - -Ti -1_11. _.1:_ -I _" i _'; __ I 11II II I j I I I 1I-t'-I*' __ , _7 [. i IL -4 . -1 7 ;I! 7 - 1- t - I t - _ _+ I , L , -1 = II - i -1I Hi I II . -I--tI I ,I 4 I L I I . t I i- _+ " . _IU 1I1-11 I II _!i _1iI--.!I ' _, -1 - IT,- = - i T , .- F--- k ... L l1-I-t I ] I I,,,I--1-1 I: I iIi i.I II ; iI I-1 ,.4., 1I 1LI - H it l-I - - I ff-F -_ LI - -, -_t . --1 -' ._..1- - - __ : a_i--;-; I - - -, - I71i I # ;: r :.W. - - -'- - I - I- -f- __7 , , II-lT-!--.I-i fI T' -1 - 4-_; -- -i-1-1 - ___i_ i :* i - -: I I I I I I I : - : 7 -r __ : -I . !- .-- I I 1111 1 1, I +_!-i . '. 11. i I -f+ - ! I,I I , I I - , V I-- -4- j-1- - .1 -I ' 1 1 1 ,II 11:1 ____ II TT --t I-,- -I- -. I- -1JI ,, I -1tl H -1 ---I " IEJ I -r- -.i 't T*i -1-S I T[ ' , II. I ,, , 4I I I I- I I TI I I I I i I I I# +k ' L- i I -1 -1, - 4-1 1 71 . I ; I t-, -I -r I I Ii _ t , I I'-. # 4I 1 I- ; I ___ r -_ , 1 __ - - : - I .H ITI1-1-:- I I- I: rii H -, 1 ! 1 - I- _ i --, I , I I ; - I-T ' 4 -i I- I - : I , -I T I I I-11 r _ .1 " im I I I ___ - H -1-1- I- I L !.__., I - I L- jtq . T i -.--!-I. LI"_ 1 1H 1 I III , - t - . I -L' I-I I -, - ' 7 -- : !_ ! _. _ '_ ._ . _177. _. - . :j --774 -I --. -r I-, '-Il I] ]E t 111 _111 - I I ,. 39 Figure 9. F- t fiJ - ..... 7H i- * tF' L4T - - 7 h i 4 U ld f4 1LS .p 1 b1 1 I 2+ i 2- I'I F 4 . 2 1 t 41 1 + 4-- - VLI 9'; -r - -f7 - -mi- - + q - A 7-14 11~ 4T -F ' n 4 4 t- -7 di ll ~ T . I I I I 'I HA _Tj E - : -1 t I - Et- T -- + 2 +- 4 74 I', It A- -4 n - T 1 1 -4 H H i - 8 T - -L - - I - I h I - T T T[ - !~~ rii 1 t - -I4 ~ 1- m2 4 T<~~~~'T q i p . -2 1 1 1.. 1 n 1 n 1_ TT F 1 I- 4 I I I II iTI F T1 *ILii1I I I T-11 3 3~ 42LL LEJ2I~ ~~7 1 4 e U W-I: ~7891 A O.gj% O10 %K in /2icaeses 4-- ii. -'I' 35 (Ontdrio) '1111111 *~1 I'll' 1~* *'1-''' II ~t *441 6 7 89 10 -- 40 TABtL1 I K AND Rb IN IETSORITES AD ROOKS AARb L lihates a~lEffde Homestead CHONDRITESS a #&Olates Va r Uorr. oorr. 0.11 0.0013 0.0012 85 Ranoome 0.18 0.13 0.00019 0.0014 95 Hayes Center 0408 0.07 0.0007 0.0006 115 Waconda 0.10 0.09 0.0011 0.0010 90 Assn 0.11 0410 0.0012 0.0011 90 Holbrook 0.09 0.08 0.0009 0.0008 100 Bj3rbole 0.11 0.10 0.0009 0.0009 90 Paltask 0408 0.06 0.0006 0.0005 120 Forest City 0.06 0.05 0.0008 040006 85 Hessle 0.310 0408 0.0008 0.0006 130 Kernoave 0.11 0909 0.0009 040007 130 Barratta 0413 0412 0.0014 0.0013 90 Moos 0.12 0411 0.0011 0.0010 110 Tennasilon 0.11 0410 0.00009 040008 125 Muaroe 0.09 0.07 0.0009 000007 100 Long Island 0.06 0406 0.0011 0.0010 Beaver Creek 0.10 0408 0.0008 0.0006 Analyst, W. H. Pinson Triplicate averages *** Chondrites average 6)SSai,"i phase 60 130 41 eftates eta Laumpkin 0.07 cangas 0.10 EStacado Warrentown r~Erro's u'ar 0.0008 0.0007 85 0.08 0.0010 0.0008 100 0.09 0.07 0.0008 0.0006 115 0.06 0.06 0.0006 0.0006 100 K AD MaG EANU b N E1 TT8 AND e "T0 S i 11ets rn= RIT- aates pallasite olivine (0.001 Ohladnite Johnstown Carbonaeosos ohondrite, Orgueil awr 0.001 MO fl-a - <0.0001 an---a -o x677.no- (0.0001 --- 0.019 90 .o..- ---- son Carbonaoooas nodle, He ase Thktito Annam, Indo 1.74 o--- China Tektite, N' 0.018 1.74 Cambodia, Indo China Tektite,2.I* -...... 1.83 go n 0.018 100 42 AND RB Sample IN 3ABASES e ao tioa R1140 Diabase 0.631 0.0097 68 11147 Graaophyrio diabase 1.61 0.0356 48 111148 Oliviae diabase 1.33 0.0fl6 115 Gabbro 0.79 0.0100 79 Graaophjria diabase 0.86 0.0120 71 1.34 0.0180 7b 0.97 0.0180 54 0.96 0.0150 64 0.60 0.0100 50 R1323 0.52 0.0079 66 R1324 2.30 0.0320 72 0.60 0.0130 46 1.64 0.0230 71 1.01 0.0130 78 68 R1314 "t " R1518 R13220 R14b0 R1468 Altered diabase 0.46 0.0068 R1470 Graaophyrio diabase 0.75 0.0074i 101 R147b Altered diabase 1014 0.0180 64 11480 Diabase 0.74 0.0071 104 R1489 4ltered diabase 0.25 0.0023 109 R7f08 Is a Dalath gabbro specimea. Specimens R1147, H1322, R1324 and R1328 are fron Ontario, Mataohewan area. Balme are from Ripiesiag area of Ontario. 43 Description %K 'flIioate Averages R149 Altered diabase 0,54 0.0087 62 R1497 Sheared diabaso 0.66 0.0150 44 Olivine diabase 0.93 0.0074 126 0.65 0.0050 130 0.32 0.0037 87 Altred diabase 0.37 0.00? 100 Granophyric diabase 1910 0.0150 73 1934 0.0230 be 0.89 0.0100 87 0.0180 68 0.0290 b7 Rl016 R1506 flbZV R1627 R161 ElbZG Riba1 Rib39 Rib50 " " 1.66 44 s& sal e - a a saaan iption g. %K/JIb % Ka E 69 Acid granophyre 3.06 0.024 128 Melanooratlo told granophre 2.60 0.022 118 Basic hedenbergito granophyro 1.01 0.007 144 Faalte forro- 0.72 0.006 120 1907' Hortonolite terrogabbro 0.27 0.0015 180 Z661 Gabbro withoat olivine 0.0 0.0016 188 4067 Olivino gabbro 0.24 30b8 4142 ,gabbro 141 MISELAKK0US ULRAMAFICS I K Rb %K/Rb gAsiwi Dauapton 3,44 Aaorthosito, Split Rook, Minn. 0.05 0.0005 S-49 Mica aqgitb 9efIdotlt*, Aarfroeboro, Ars. .4.6. 0.11 42 ------ Kimberlite, 3. Afr. 1.7 0.028 61 50-10 Lhorsolite, Baltimore, Ad. 0.015 <0.0002 --m S-b7 2irozenite, Wbter, 3. 0. 0.,001 <0.0002 Saxonite, Riddle, Ore.0.004 (0.0002 - an- 100 -- 45 U90"MAMAFIA$ QE uI $S AltO Sample MPANlS %K/ab Devaription xge! P140 Danite, Balsam Gap, 2141 L ~0.001 (060002 -- Me- G. Serpentine, ~'0.0005 e-- -O <0.0002 -- --- Serpentine, Bele-~.0Q35 <0.0002 --- Ser pentenised dan- ~0.003 its, ig,'s Mine, <0.0002 o-e---n ~O.011 <0.0002 en --- .C.~'0.004 <0.0002 -- Geiger's Quarry, 4 Wa sh. Daite, Twin Sistere Mt., Whateen, 0.0004 P18 ders Mt., Vt. P3x0O Wt*;;. P369 Websterite, 231 Daite, Addle, -- 4. Webster, N. C. -- -e This Sale of roots was analysed for radioaotive content and stadied petrographioally by 0. L. Davis and i. H. Hess, 1949. CHAPTER IV BARIUM AND S U Historg-al ReLgws $N MEfITES ND X The determinat ion of Aa in silicate meteorites is due almost entirely to the work of Ida and W. Ioddack (1930), and to the work of Wolf von Engelhardt (1936). Goldschntdt (1937) reeloulated the abundance values. DeSerminations of Sr in meteorites are based on the work of the Noddaoks, W. Boll (1934), and G. v. Wudrstlin (1934). evesy and K. Largely on the basis of these values H. Brown and 0. Patterson (190) have calcalated oosmic abundance valaes for the elenents Sr and a. Hevoesy (1932) has oompiled abundance values for Sr and Ba in stony meteorites from nis sad *irstlin's analysea and the analyses of the ioddaoks. Rantama and Sahama (1950), in a review of the literature, also derived abundaace values for lr-and Ba. Abandant analyses have been made for Sr and Ba in terrestrial roax Sanama . and the literature is reviewed by Rankama and loll (1934), Bevesy and Wilretlin (1934), and von Engelhardt determined Ba and Sr in various rook types. Other worters include F. Wioakan (1948) for the cosmic abundanoe of Sr, Sahama (1945a, 1945b) ror Ba in rooks of Fennosoandia, and Ba in Swedish rocka by P. H. zandegardh (1946). In the following table are given the resalts of various workers, inolading those of the writer. 4(/ Anal rt r %Ba in silicate 1 a in sp11oatt meteoriete ewer teor ites ** ,,* * Hevesy & Waretlin 0.03, 0.1-0.5 0.00 Noddaaks O.072 0.0020 Goldpchmidt 0.0026 Rantama and Sahas 0.0026 0.0009 v. Engelhardt a----- 0.0001-0.0048 Pinson 0.0007 0.0008 a i 0.0009 IndividQal analyses of the meteori tes by v. Engelhardt are listed below, showing comparison with the writer's. Name BaO 4"em"MIMP. Ua gelhardt Nakrite, Stannern,0seohoslovakia * Javinas, Franee -- 0.0048 0.001-0*003 Chondrite, L'Aigle, France 0.0003-0.001 Silicate phase, Holbrook, Ariz. 0.0003-0.001 asa~.An jLIuMuulj, bw neA:1000 be -----0.00I T Silicate phase, Ungarn ahoadrite 0.0001-0.0003 Chondrite, Erxleben, Sazony 0.0001-OO0003 eas e awes "I * " Chantonnag, France 0.0001-0.0003 " Barbotan, Frane 0.0001-0*0003 " Aviles, Mexico 0.0001 , bjub'le, Finland 0.0001 0*0008 "* Pltat, Poland a-- a sea 0.0007 Reyesy, 1932. ** Heyesy and Wairstlin, 1934. w----- 0 Simarly, a table for Sr is presented. Namae 0 S sOmy 44 o Wurstlin y _& Waconda, Kansas es. 0.01 Ouanta, Spain " 0.01 Paltash, Poland " 0.02 0.0007 0.02 ------ Vigarano, Tabory, Piave, Italy 0.0009 0.03 Russia Karoonda, ' South Australia " ? ------ 0.05 ------ Revesy and Warstlin used x-ray spectrographic techniqies. Thus it is seen that the work of v. Engelhardt on Ba is in reasonable agreement with the analyses of the writer. employed the optical sp*etrograph. Both The writer used new im- proved quantitative techniques for determining trace elements - tno addition method, wherein a typical ohondrite was used as the matrix material rather than a synthetia standard. Ba and Sr were added as W-1 and G-1, which have been independently analysed by several other workers and are based on mean values. The analyses of Hevesy and Warstlin, based on x-ray spectrographic sechAiqes, seem to the writer to be in error by a factor of at least 10 for Sr, and it is sugested that these valaes be no longer used in computing oosmio abundance valaes. Recalcalations of the results of the Moddaoks and Hevesy and Wuratlin by Goldschmidt (1958) led to the conalusion that Sr * Fairbairn, H. W., U.,..S. Special Ball., 1951. 41 was more abundant in silicate meteorites than Ba. The re- salts of the writer's investigations indicate that Ba and Sr are almost equally abundant in meteorites. On the basis of the present analyses of the writer it is suggested that the abundance values in chondrites be revised to jir. 0.0WS% for Ba and cir. 0w% for St, and that these two elements are present in a ratio of approximately 1 in chondrites. Chondrites comprise over 95% of silicate meteor- Beoaase of the low concentrations of these elements ites. and spectral background error possibilities, the values, n-. pecially that for Ba, ay be slightly high, possibly as much as 20%. Gooshemistry of Ba anA Sri Stroatiam and barium are widely distributed in the rooks of the Earth's orast, and are among the most abundant of the traco elements. However, the quantity of Ba and Sr concentrated in minerals of these elements, e.g., barite and celestite, is relatively small. Fur- tnermore, the barium and strontiam minerals are chiefly products of sedimentary and hydrothermal or pegmatitic-hydrothermal origin and are not believed to be mineral products of magmatic differentiation. When contained within a cooling magma strontium and bariam substitute and are captured within the other minerals. Following are listed the ionic radii for the four elements which commonly freely substitute for one another, specifically 50 Ba2t for X and Sr2t for Ca2+ Oa2 + - - 2+ - Sr Ba K + - . 0.99A - - - -C - o - 1.12A 0 1.34A a 1.33A From these ionic sites it would be expeoted that Sr 2 + and Ga Z+ would readily sabstitate for one another, while Bat2 would follow Kt This generalisation has been found to be true by observation. The mineral distribation of Sr and Ba has been tally discassed by Rankama and Sahaa (1950). Ob- servations in this thesis will be confined to the meteorites and rooks investigated. Sr and Ba in Meteorites: On the basis of twenty-one ohon- dritic analyses, the average Ba and 3r content are given below, and are compared to values derived by v. Engelhardt, Hevesy and Wurstlin, the Noddacks, and Goldschmidt. The working curves used in determining Sr and Ba in meteorites and rooks are oontained in this chapter. The spread of points in these curves serve to demonstrate the degree of reproducibility possible by these spectrographio teohniques. The following table com- pares the writer's results with carrently accepted values for Sr and Ba in silicate meteorites. %Ba Sr 4* Pinson .Bnejn flhjl 0.0006 0.0007 0.0009 0,0026 Ahrea, L. H., New Ionic Rettn4In Atoa). *~Rankama and Sahama, 1950. j 1aestilgators, sor press, Geocheimica Table II gives the analytical results for Ba and Sr of the writer's investigations for individual meteorites and rocks. It is seen that the weight percentage values for Ba agree well, but taat of Sr is smaller by a factor of 3.7. Two of the stones analyzed showed anomalous Ba content; the Rancome's Bridge, B. C. stone containing 0.0032% Ba and the Long Island stone containing 0.0110% Ba. The analysis of the Long Island stone was not included in the averaging for Ba content for two reasons. The specimen analysed was badly weathered and has conoeivably been contaminated with Ba. Secondly, the near constancy of the other meteorites in Ba content suggests the Ba content for the Long Island stone not to be representative of chondritic meteorites. In all other specimens the spectra of chondrites were remarkably similar. The danger of error in relying on composite samples is demonstrated by the anomal. ously high Ba content of the Long Island meteorites. This specimen (weathered, however) contains 14 times the average Ba content or the other meteorites analyed. zeoluding the Long Island and Rancome's Bridge meteoritem, the Ba content of the other 19 chondrites is remarkably oonstant, with a maximum variation of only 6 parts per mile lion. In all twenty-one obondrita analyses the content of Sr is remarkably constant, with a maxiamm variation of only 7 parts per million. 1t flObb, rbasonable to believe that Sr and Ba are present in almost constant quantity in silicate meteorites, on the basis of these twenty-one analyses. The variation in content is approximately within the factor 2. This factor may, in fact, be smaller, beoause its magnitude is partly due to experimental error. Probably it is not larger. It was hoped that this investigation possibly would prove that the qantity of those trace elements which are restricted to the silicate phase (Sr, Sa, Sc, alkali elements, eto.) would show that their quantity depended on the amount of free metal phase present. This relationship has been demonstrated by Vrior and others in the ease of Mg and FeO, and is fully disCassed in this thesis in the chapter on mineralogy. However, it is concluded that the results of this investi- gation are not sufficiently acourate to warrant such Oonolmsions for Sr and Ba. The relationship may exist that these elements are very nearly constant in the silicate phase, and the total qaantities in the ohondrites are leseeod proportionately to the amount of free metal present, but more accurate analyses are needed to prove it. Spectrographic analysis with use of an internal standard should be able to establish or disprove this hypothesis, and fatare work of the writer will be along this line. RanXama and Sahama (1950) conclude that BaZ# cannot substitate for Mg sizes. because of the great difference in ionic However, in the case of Fe-rich olivine from a palla- site of this investigation, it is seen that Ba in present as 0.0007% oomparable to that of the ohondrites. Srt ion is, The smaller on the other hand, definitely impoverished. The sam relationship holds for the bronsite analysed from the Johnstown, Colorado, chladnite. Ba2 Since neither Sr2 nor would be expected to fit into the olivine or bronsite lattioes, it is reasonable to believe that these ions were entrapped -- that orystallisation was too rapid for their es- *ape (differentiation), These large ions shoald distort the bronaite and olivine lattices, and measarement of the lattice constants by x-ray diffraction methods may enlighten this relationship. Srz+ seems to have been largely exeladed from meteoritic clivine and bronsite, and thz it is auggested that in the chondrites Sr2+ is a oonatitUeat of either the rare cnloio plagioolases, or more probably the abwdaant interstitial glassy material. Chilling in the former planet's interior may have proceeded too rapidly to allow normal sabstitution of these two elements into crystal lattices. Sr ana Ba in the Skaergaard suite: The analysis of these rooks for Sr and Ba has already been done by L. R. Wager and R. L. Mitchell. Although the Skaergaard rooks represent a wide range in composition they are believed to be the resalt of the difrerentiation of a single intruded magmatic body (Wager and Deer, 1939). Although the elements Ba and Sr have already been analysed for by Wager and Mitchell (1943), these elements were again analyzed for by the writer because Sr appeared to be reported as unasaally abundant for these types of basic rocks. Wager and Deer reported 0.2% SrO (or 0.17% Sr) present in the original Skaergaard magma, as represented by the marginal olivine gabbro, and state "SrO, as has already been noted, was particularly abundant in the original magma." It is suggested on the basis of the writer's analyses that this conclusion is erroneoas and das to analytical error, The value 0.2% is ten times larger than the amount in Noll's * ** and Daly's average gabbros, and is almost equal to the potash content -indeed an anomaly. Petrologists would indeed like to believe that the original Staergaard magma was in no way abnormal, for this is probably the most thoroughly stadied example of the fractional crystallization process daring magmatio differentiation. The variations- for Ba and Sr from bottom to top of the Skaergaard intrasive are shown in FigareZ. AThe results of Wager and Deer are plotted for comparison. The trends of the two "oarves" are sympathetio, and the analytical agreement for Ba is reasonably good. However, Wager and Deer's values for * W. Noll in 1934 prepared a composite sample from 14 gabbrolike rooks for analysis, and 14 gabbros for analytical oomjarison. * R. Daly in 1937 likewise compilated from the literature the composition of an average gabbro and an average granite. Fi jure 1. 0-0201% Sr *.007%8 -. 0,1 '%* VARIAT/ON OF Ba & Sr IN V7 S/'A ERGAA RD IN r US/VE Analyst, Pinsoo AnMa/ysts, C I,. qoET6 366/ /S 07 - a 4. 1- 42 Wager & Mthefl 'Jib /00oar 0a L% 56 Sr are approximately 7 times those found in the present inYestigation. The spectrographio plates were rechecked and the values found in the present analyses seem to be correct. It is Qoncluded that the anomalously high Sr content found by Wager and Deer in the original magma (marginal gabbro) and the suacessive gabbros were due to an analytical error, and that the Skaergaard rooks contain a reasonable and expected amount of Sr. SrZ+ is shown to vary sympathetically with Ca2+ ions are of like charge, and although Ca These is somewhat smal- ler than Sr 2 + (0.99A and 1.12A) the difference is less than tae 20% of the empirical geoohemical rule stating that solid sabstitution to a significant extent can oooar only if the replacing ion is within 20% of the size of the ion to be replaced. Sr and fa both decrease abraptly in the acid granophyre phase. In another paper Wager and Deer (19Z9) have discussed the olivines of the Skaergaard rooks. Although this remarkably complete olivine series crystallized in a lime-rich environment, the olivine minerals have remained nearly pare members of the FoS104 - MS2 Si0 4 series, and are practically free of Gaz2i0 4 . However, the experimentally observed series GaO - FoG - S10 2 suggests that these olivines should contain from six to seven percent 0a2 3i0 4. Baritam and potassium have likewise been plotted in Figare l anl the resalts of Wager and Deer compared with those of the writer. The agreement is reasonably good. Although the ionic sizes of K+(l.33A) and Bag+(1.34A) are very similar, the Ionic charges are different. However, the saboti- tation of BaS+for K + is not believetto take place as readily as that of Sr2+ for a2+(Rankama and Sahama, p.471, 1950). W. Noll (1934) oonoludes that Ba in relation to Sr is enriched in potash feldspar rooks, doe to the smaller radios of sr2+ which is entrapped in the crystal stractares of the early formed caloic plagioolaeas and caloic pyroxenes, sub.. stitating for Ca +. study of ti Thas, observation is confirmed in the Skaergaard intrusion, where the Ba Is enormously enriched. in the final differentiate, potash &aid granophyre. However, in the case of shoandritic meteorites, this investigation has shown Sr and Ba to be present in almost eqaal and constant quantities, in amoants lesser by a factor of at least 20 less than is normally found in diabasic rooks and granites, but on the other hand enriched by a factor of 10 or more over altramafio Mg-Fe rooks. This observation suggests that the silicate magma from which chondritic meteorites formed cooled too rapidly to permit differentiation of Sr and Ba, and that these elements were entrapped. It is suggestive that a value of approximately 0.0008% for both Sr and Ba may represent the true abundance ratio in the silicate magma which 58 formerly existed in the planet from which meteorites may have been derived. Ultramafic rooks: Thirteen tltramatios, inoluding seven specimens which have been analyzed for radioactive content by Hess and Davis (1948) have been analyzed speotrographically for Sr and Ba, as well as for K, Rb, So, and Zr. Noll (1934) reported Sr absent in danite. Hevesy and Warstlin (1934) reported 0.0020% Sr in peridotites, eologites, and danites, while von E;ngelhardt found cir. 0.0003% Ba in ultrabasio rocks. Sahama (1945a) found air. 0.0009% Sr and air. 0.0018% Ba in Lapland altramafies. An anorthonite from Split hook, Minnesota, which is a -alciam-rich root composed almost entirely of bytuwnite, showed 0.008% Ba and 0.029% Sr. This rook contains a large percentage of Ga (in calen plagioolase), bat is almost free of K (0.05). This is the first analysis of an anorthosite for Sr and Ba known to the writer. The enrichment of Sr over Ba is as woald be expected, although the Ba content seems a bit too large for a rook so low in K oontent. fouad a oontent of 0.01 W. Noll (1934) Sr and 0.035 in two specimens of plagioolase analysed. A specimen of kimberlite from Soath Africa contained 0.07%Ba and 0.028% Sr. A thin eetion study could not made of this rook, beoaase the specimen was received in a palverized form. However, its most abundant mineral oonstituents are olivine and biotite, which probably accounts for the enrichment of BS2a by substitution for K+. But Sr2 4 is also great- ly enriched, as in Ca-bearing altramaficas. A review of the literature (Johannsen, 1938) shows typical kimberlite to contain tremolite, a caleio mineral. Also, a visual inspection of the spectra of this specimen showed Ca to be present in significant quantities. Biotite was shown by von Engelhardt to be greatly enriched in Ba, while W. Noll showed approximately 0.0008% Sr in the biotites, which contained on the average 1.89% 0aO. F. Whiting (1951) found approximately A similar valae was found by S. R. O.5* Ca in biotites. Noctolds and R. L. Mitchell (1948). Both values are onsid- erably smaller than those found by won Engelhardt. A specimen of the Arkansas diamond-bearing peridotite was analysed for Ba and Sr. Sr content was 0.013. Barium content was 0.1%, while Thin section study of this specimen revealet it to be composed of phenochrysts of olivine set in a fine groud mesh of augite and biotite Orystals. Augite contains abundant Ca2+, while biotite is rich in Kt * Also, analyses showed 4.6% K, while a visual estimate of Ca showed it to be present in large qantity. Ba2+ and Sr t +for K+ and 0a Thus the substitution of is again found as expected. A specimen of Lherzolite from near Baltimore, Maryland, was analysed. This rock is composed of olivine and ortho- rhombic pyroxenes. Inspection of its spectra showed both Ga and K to be present in minor amounts (0.0154) as were Ba (0.0006%) and Sr (0.0014*). In all danites, serpentines, and non-calole pyrozenites analyzed the content of Ba was found to be lower than 0.0013o. This value is in close agreement with that of chondritic meteorites. The average for 10 Mg-Fe rooks of these types was 0.00040% Ba, in olose agreement with the average value of Ba in chondritio meteorites. Strontium in these rooks averaged 0.0001% Sr or slightly less. All were exceedingly low in K and Ca, as shown by examination of the spectra. Those specimens that showed appreciable quantities of Ba all contained traces of X, which thin section studies indieated probably to be present in minor constituents of mica. G. L. Davis and H. H. Hess (1949) give excellent petrographIc descriptions of the suite of seven altramafios analyzed by the writer. Saxonite, a terrestrial rock which most often is cited as closely resembling stony meteorites in mineral composition, was found to contain only a traes of Ba, 0.0005% Sr. 0.0001% and Thas both Sr and particularly Ba are lower than in meteorites. This observation again demonstrates the im- propriety of comparing this rook with meteorites, particularly on a basis of mode of origin. Figure 11. Vt~II- - - - - - - r -- 61 -- -T -. T1 . 7,< - ------ ..- -7 -FF 1 - -- - -4 L11 - ]T K- : F7- 1I --4-- ---. r- -7- 7 - {- 7777 4- -- - -- - .- 41 1--i K--I - *j~* * t it ft- -- 4-- 4-n L - I S - - -F-j - t- - -- - - 1 F I - i- _ 4- : -- ii"-" - - - . -4- F - - 7--..-i -4- - - i -T-- - - -----v--n --- -- - - - - - I I --F -- - F- -~- - - I - *1 -n--F.- }.', -t7---+~ -~ t l Fl L1 ~ -'-K----- -- *1 F -- \- \ - '- - -'4- I- K to -- - --_ p I- K ~ -4-- -A -- - T- --q 42 .117 K ~-H-* TT-1 K 1- 7-1 --1.77-j iI -T- - -F- i7 -'-CA N - F--- - - t -F. 4-i - --- 1-7 F. . '---4. 7: -D. f V -- -- -j ] - -77>P - r i -,r- - | -1- - --- 62 Figure 12. - tt* -$ [ - u "-H -~ H+ ~ IM H +LHL ~ -~ - u - -~O ~ -- 4- ~ 7 t Tr 1-7 :- ----- TT Hr-7 - u t 1 110 .9-77 r 7 H -L u 11f -HL Ti . _ l - T-1 7 +H+1- 4- 7 H T__ --L~ uL u a1 u V 7 u r -H H + -- TT t-it HFr- ++T++J_ -H1 -j _I_ - +---_+ -1 - t H H c 1+r HW TTTT -1 t - - - rTP -- - TT -+l tI - -i -Tr -d - -I -F -L -, _u ' - -T H+H+T - --Fi l F -1- - -j 4 - 1 - T Tj L" - -1 -i -L - T - Tr -~ -) -- L_ i i u H+ -I 1rr- - .T . T -- L 1 -I T7 +H++ i 1 -- L - r - Le L uL . 0+H+ T 4 I Ft - r - L - +-A+H -- 1i -T -T n~~11 d 7 - 17- - - -Ft --- T T T u TLu 7-- i - ITII u +--H- TT - ~~~+H-a++++ --++ +4 2+ 0.0010 ++++ 4000A0-0oooO 0100'0 *hO0'0 06 8 0 6 8 I1 9 ' .1'91 40I s - w' Zov 4a - ps t extyi4 -,k4n .6 ev --.--. . ! -- i 7i., '' 9 H-1 9 * e It I -ro Figure 14. I I- 11 . -M II 'I - i I 10 11 I t - I .r 00,i I LirlI I 4 5 9 10 0.010 H w- 3 6 4 0.to0 !-o $Efl UT 0*t noURflif *' 9000*0 0100*0 Qt00'0 9*0 sestTw ; 80fl#AS *IOTTdTA* Jo POVI"TPUT *"s fOT$dtOSDenit.* £000*0 000*0 90000 0000*000 9000*0 £000.0 07.0040 &000*0 90000 6000*0 9000*0 8000*0 A0000 9000*0 £000.0 9*0 £000*0 6000*0 9000*0 60 90000 0100*0 6*0 01000 2100*0 £000*0 6000*0 9000*0 6000*0 0100*0 tT00*0 6000'0 9000*0 0*0 6000*0 0t00'0 9000*0 900 6000*'0 6000*0 80000 Is0ps000l fl00% C000 6*0 60 Vlt 6*0 'flo sttwtw *oavrnN IT000*0 6000*00 *xrioun A000*0 9000*00 flTo ssoj $000*0 6000*00 8000*0 A000*00 6000*0 £00*0O 9000*0 £0000 tocroo c1 t00*0 nTOO 9000*0 90000 *9000 Woo' 0 "'pim't Sn 9000.0 £0000 ~pge eaog aVitos 0 e S3HR~ Y * xII 'TY Let -U@o eegwj iiY 66 i 4Bates 4 !"toro oates Gor 1 e /Sr u37r- Lumpkin 0.0007 0.0006 9.0007 0.0006 1.0 Cangas 0.0007 0.0005 0.0008 0.0007 0.8 Estacado 0.0008 0.0006 0.0008 0.0006 1.0 Warrentown 0.00005 0.0006 0.0006 0.0005 0.9 gLa ASA. I ITE3SD MiIELA fioUS METEOLIL*AS rwrr -3. C. pallasite Olivin* 0.0007 0.0007 0.0001 0.0001 6.7 Culadnite, Johnstown 0.0006 0.0005 0.0002 0.0002 2.3 Garbonaq. 0.0003 esous ohonaritto ---- 0.0004 0.8 Caz bonaqe OLas------ 0.*0008 ---- 0.9 TeXtite, Indo China 0.*000 - - --- 0.0075 4.0 0.*032 --- 0.0087 3.7 0.0085 4.9 Orgueil nodale, Heable ---- ?.kt i toI Tektite, Palo 0*042 6w Ba AND own" Sr IN SKAERGAARD ROOKS mab a NOa sample Desgriptiona I gSo fliariges 3068 Ba/Sr Acid granophyre 0.081 0.0081 Nelanocratic acid granophyre 0.07S 0.010 1905 Basia hedenbergite granophyre o.O6 0.035 442 Payalite ferro-abbro 0.013 0.008 1.6 1907 Sortoalite ferrogabbro 0.006 0.018 0.35 $661 Gabbro withoat olivins 0.010 4067 Olivine gabbro 0.007 10.0 7.5 10.3 1.8 0.020 3.6 ISCZ2 ANECEIS ULTRAMAFICS %Ba/Sr SaMp loleription teragesS-44 S-49 a--- ------ as 0 V1g, Anorthosito, Split Rock, Minn. 0.0008 0.029 0*28 Miea augite peridotite, Murfreesboro, Ark. 0.1 0.013 0.77 Kimberlite, S. Afr. 0.07 0.028 0.25 Laerzolite, Baltimore, Nd. 0.006 0.0014 Pyroenite, Webeter, . C. 0.0013 0.00016 8.1 Traes (0.0005 -- a -Saxoite,Riddle,Ore. ?,Praoe 66 ULTRAMTAFIS OF HESS AND DAVIS sane Description 3r Averages &0.00014 P140 Danite, Balsam Gap, N. 0. 0.00067 P141 Serpentine, 0.00081 A 0.00005 16 0.09070 (0.00005 My Geigerr's Qarry, Wash. P145 Dunite, Twin Sis- tere Mt.,Ahatoon, P318 Serpentine, Belvedore Mt., Vt. 0.00050 A. deteted PS20 SerpentInised dsanite, Zlng's Mine The t ,Pf.4. 0.00049 (0.00005 2369 Webe terf to, Webster, E.. 0.00004 ~0SJ002 27 P391 Danite, Addie, 5.0. 0.00055 ~.-P0 2.7 08o -- CHAPTER V MTEORImhS AZI RociS S0 AD hINER Utetorical Revie; Rankama and Sahama (1950) have reviewed the literature on the abundanoes of So and hr in meteorites and rocks. The Noddacke (1934) found 0.011% So in a composite sample of silicate meteorites and 0.0006% So in terrestrial rociks, V. . Goldeshmidt and CX. Peters (1931) analyzed a large number of minerals and rooks and twenty-six meteorites, including roarteea ohondrites, olivine from a pallasite, and a onlaAnite. Goldsohmidt and Peters found 0.0000 - 0.001% So in silicate meteorites. (193U) W. van Tongeren compiled abundance values for rare elements, includR. Brown ing So, in the rooks of the Datoh East Indies. (1949) compiled cosmic abundance values for both So and hZr. Zironium was determined as 0.010%in the silicate phase of StOy ateorites by the Nodttaks (193Q# from a composite sample, and In the metal phase as Q.u00% hr. Warstlin (1934) determined So as Hevesy and 0.010% So in silicate meteorites, by the analysis of a composite sample composed og 40 meteorites representing £0 separate falle. Hevesy and wuaretlia employed x-ray spectrographic techniques (1932), while the other investigators used the optical speotrosraph. Revesy and Wurstlin also determined hr in numerous minerals and rocks and in several individual meteorites. zr was do- 70 termined in some igneous rooks by van Tongeren (1938). The Nottacks determined Ht as well as Zr in silicate meteorites, presamably by chemical conentration and spea- trognphio methods. Goldschmidt and Peters were unable to detect Y in metorites, and reported 0.0001%Y. The present writer was likewise unable to detect Y or Uf- in meteorites, nor any of the rare earths. Cerium, La, and Y were sought but not found. ScandiAu G0oaemistry of Soadiu m: Soandiam, Z = 21, is of ten incladed in the grotp of rare eairth metals (Z = 57 for La and Z = 71 for La), because So in closely similar to the rare earths in chemical properties and in geohemic distribation. Yttrium, Z = 39, is often included for the same reason. These similarities of So, Y, and the rare earth elements (or lanthanides) are due to the lanthanide contraction, whereby, starting with La, additional electrons in sacoseeding elements are added to the inner N shell, and all the elements of this group remain trivalent. Beoauise of the increasing nuclear charge-and the electrons being added to an inner shell closer to the nuoleus, there is a compensating contraction of the ionic sizea, with the result that all of the rare earths are or very nearly equal ionic sizes. The population of the outermost eleotron shell remains constant. Scandiam, however, is of smaller size than the rare earths, 71 which accounts for the fact that its geochemical behavior is somewhat different from that of the rare earths. So in ateorites: Scandium was detected in all twenty- one ohondritos of this investigation. ly constant amounts. It is present in near- In the silicate phase it varies from a minimum of 0.0006 in the Warrentown, Missouri, specimen to 0.0013 in the Homestead, Iowa, specimen. Analytical results for So in rocks and meteorites are given in Table III. So was not detected in olivine from a pallasite, which seems anusaal in the light that Soc+ is usually thought to substitute freely for Mg2+ and Fe2+ of similar ionic size in early magmatic orystallates. The average abundance value of Sc in the ohondrites analyzed is 0.0006%; that of the silicate phase of chondrites is 0.0007% So, as determined in the present investigation. These valaes are in close agreement with those of the Noddacks, who analyzed a composite sample, and with the values quoted by Rankama and Sahama (1950). Goldschmidt found O.0O1 So in the Rosestead meteorite. One obladnite, Johnstown, Colorado, an achondritio meteorite composed of approximately 98% bronaite, 1.bf free metal, and 0,5% YeS, was fouand to contain 0.0014 analyses of ultrabasio rooks by Qoldsohmidt (1934, So. Many 1937) and Sahama (194b) have established the fact that pyrozenites contain the highest percentages of So. Thus it is not surprising to find a meteorite oomposed almost entirely of bronaite, as is the Johnstown okladnite, to contain a greater abundaaoe of So than any of the other meteorites analyzed. Soandium was first believed to be one of the rarest of elemants terrestrially, due to the fact that 6oncentrations of this element are rare (thortvsitite, 3023107 is rare, and is believed to be the only So mineral known). With the dis- oovery that So was camoaflaged by substitution in the crystal lattices of many common minerals, the known abundanoe of So was greatly increased. Thas, So in igneous rocks is as abun- dant as arsenic and 1000 times as abundant as gold or platinam. On the basis of a cotve, plotting the cosmic abundanoe value of the elements against their respective atomio numbers by R. Brown (1949), it was suspected that previous ara. lyses on which the value for So was compiled we too low. However, results of this investigation, as well as of the investigations of L. H. Ahrens on oommon rook types, have failea to raise signirioantly the apparentLy low abundance value for Sa. So in the gaargaard rooks: This element has not been previoaly determined in these rooks. Analyses by the writer showed an expected enrichment by a factor of approximately lb from base to top of the intrasive. The variation diagram for So in the Skaergaard intrusive is shown tA graph accom- Fi~u.r~ ib. IArTOIv /,IV~ t t Zr & SAM 7$4 T4 ARD I I I 11 41t2 I 4 :Q 'lb Ii '4 'lb I, 067 366/ 1 $ q##Z qt'12 90. 6b 70* 00" panying this section. So in altranafic rooks: Goldschmidt (1939) reported a maximum value of 0.016% So in pyroxenite, and found that So is enriched in augite (separated from eruptive rocks) and in garnet (separated from eoclogite). Garnet from eologites is enriched from 2 to 10 times over pyroxene in specimens of sologite. In the present investigation So was found in all specimens analysed to be present in qantities of the same orders of magnitude as in the silicate meteorites. our in the metallio or sulfide phases. danite averaged 0.0008% So. So does not oc- Three specimens of Goldschmidt and Peters (1931) found from 0.0005% to 0.001% So in seven dunites analyzed. Goldschmidt reported 0.0005% in kimberlite, while the analysis of the writer is 0.0017. Thus it is seen that the present investigation agrees closely with the work of Goldschmidt and keters. Scandium was detected only as the barest trace in a specimen of anorthosite from Split Rook, Minnesota. Goldsohmidt and Peters likewise found So either absent or present as barely detectable traces in plagioolase foldspars, and it is concluded that So is excluded from plagio- clase crystal lattices. In eruptive rooks it is confined chiefly to ferromagnesiam types. I. Oftedal (1943) observed that nearly all the So in igneous rocks is contained in biotite, pyroxenes, and amphi- boles, and found a maximum of 0.0150 So in pyroxenes from basic igneous rocks and 0.0300' So in hornblende from a hornblende gabbro. In biotite and muscovite from granite pegmatites he found as high as 0.1% Sc. Oftedal contended that Sc aould be used as a geologic thermometer if other ferromagnesium minerals were not present in the rock, for he believes that biotite is always saturated with So for given temperatures. Higher temperatures are believed by Oftedal to exclude So progressively from the biotite straoture. The writer saggests that this So thermometer may poa- sibly be used as a eriterion of granitization. Zirconiam Gooohemistry ofZr: Zirconium, boause of its large size and high charge is believed to concentrate progressively in magmatic residual liquids. Zirconam content is low in early magmatic crystallates, for Er oano -readily substitute in the crystal lattioes of early formd minerals. Zr in meteorites- All analyses for Zr were made by visual inspection of the line Zr 3591 and comparison with W-1 and G-1. Analyses for meteorites and rocks are tabu- lated in Table III. The Zr content of silicate meteorites was found to be remarkably constant, with a minimum of 0.002% Zr and a maximam of 0.008% Zr (LampkinQeorgia, chondrite) in chondrites. The average for twenty-one ohondrites is 0.005% ± 0.001% Zr, a value approximately half the ourrently aocepted valas (Rankama and Sahama, 19b0). The Noddacks (19Z0) reported 0.0008% Zr in the metal phase of meteorites. However, on the spectrograms of the writer, with dispersion of 2.53 A/mm, interfering Fe lines prevented analysis of the two most sensitive Zr lines in the metal phase of silicate meteorites and in one specimen of Canyon Diablo iron meteorite analysed. 2& in Sastgaard rooks: 4he Zirconiam had not been previoasly determined in the Skaergaard rooks (Wager and Mitchell, 194Z). The characteristic enrichment from base to top of the intrasive in Zr is shown in a variation diagram in this chapter, £r UJ utramfialrok: Zr has been determined visual- ly in several altramsfic rooks by the writer. All speci- mens, except kimberlite, which is rich in btotite (and X), are low in Zr content, ranging from the barest traos ( (0,0005) to 0.004% Zr. A specimen of mioa augite peri- dotite, which contains approximately one-third as mach biotite (and K) as the kimberlite specimen, contains 0.Q00 Zr. Saxonite from Riddle, Oregon, which reseables chondrit- ic meteorites in gross silicate mineral composition (olivine and monoolinic pyroxenes) contained only a bare trace of Zr, and is impoverished compared to chondrites it Zr by a factor of at least 10. 77 Figure 16. 1 a _ [ ' 4 --- I 1 -± i T ~4i- r 777-17 .H 7 0 !I :j i+f7 717 - - - - - tm-I 4 -- - : 7 - - -7- -- - 7 - - -- - - I! ---L --- - g -T-- - T -- - -- - ---- -1 - - - --. -- ---- - - -- - --- *-- -- I ~0 g *1 7I - Ii - I - - - 1 - -it ---__ -- -F- - - 1 .K *- __ - - a -- F- -" ! --- --- - 1- 7I . 7 1 .1 - . . . -= J -7 7 . 1 _ II i~ I wa2LKL _J t-- --- - I p -- p 1- ~~ ~~~~ ~~ ~~~~~ I~ - i1- ::I I i I. .. 1 I i. . - L7--. . . . . . II.]II .I . 1. . . .II- 1i - : 0 Figure 17. t 7 -I44T -- -, 7 1 -; r $- 9 3-j- - --- -- ;- - - H + r- +H 4 -- - - -- t t r ifHI 4- > - trt - - +'IJ +1, TI A +j -- 7 tfl! T-p -kr -ij-H - -l - - 11 i- -14 -1 <I t -4 t]n -- J-S 2L4i 4 4 -n4 Hit - F4 -4 - 4B T4-- -i I lfiI. Hi r T 2 - Tl-4-L - I - -- - -17 -- - --- -1" t I a-'- 6~~I II H " H4++ -itt- L t tij I t$ l 4 - - TlTt lit!. L .. - I 471L I112111 LL :II -4-- ------- H+ H -I r t-1t -I M - - F: ,-- - -- 44 T 1 4- - t 1 1 'I___ nt T______ h4 1 if -- - - H >r±'I t I L i J I A IT t 14 35 6 7 8 9 10 Se in Aeteoritel (hetel C 8 7 *e 9 1 %- a'L6 oogo-o 9 L 9 O1 6 8 9 I 01060 8 L. 01.6 g %p, 9 L 9 g t [ P q i iii omunnuonnunommmumomua;amunans a mnomnnommaasmem L 6 Ok L.L MMM~~~~~~~~~~~~ Ioounmamammmmmnmine~e~imn ammomamanso emmassammmmmmmanummmanneassmmusmum ======= i- 11 L-m--ammsamsmm I so [eomm-su-em I Isae=== "Iomnnao~lnanma imammmminasmammmamOrr-mmmm I mamsmasaammmnuanm== nnIF nI 8T *J!MPTA 1o it 80 Figure 19. II II! I II ~I I I I I I~~~~~~~~~~~~~~ ~~~~~ ~ ~~ ~ ' I III -II .1 .111 '''' IlL iF1!IIIIIIIII I IIIiIiiIIIIII II I ILl I TTTT 11.11il i I I 1A L - L -L .. I I I - J.t IJ. ]II11TEE L TTL I HHA 1 11111111111111111111-M MM i l 11111111 1 1ill rlm !llli!llll!111111111!11111 1!111111 1 111111111 3 4 5 67 8 9 10 7 8 910 0.6001 G-1 0.0610 1 111l 11 1 1 1 1 1 11 1 1 1 1 11. i i i ! i i tHIIIIII 3 j 1111M IT I-ml - 81 TAbis III $4 AAj ZI MESTORITES AIi So zri ate$ W-sa ROCKS CEONDRITES 0 care- a~ees tE 4esr Homestead 0.0013 0.0012 0.000 0.0045 Ranome 0.0006 0.0004 0.003 0.0022 Hayes Center 0.0007 0.0006 0.005 0.0046 Wacoada 0.0008 0.0007 0.003 0.0028 Assan 0.0008 0.0007 0.003 0.0027 Holbrook 0.0010 0.0009 0.003 0.0028 Bjarbole 0.0006 0.0006 0.00b 0.0047 ultusk 0.0007 0.0006 0,004 0.0032 Forest City 0.0010 0.0008 0.005 0.0039 Resale 0.0012 0.0009 0.003 0.0024 Kernouve 0.0009 0.0007 0.003 0.0024 Barratta 0.0006 0.0005 0.003 0.0028 Moos 0.0006 0.0006 0.003 0.0029 Tennasilon 0.0008 0.0007 0.003 0.0026 Manroe 0.0006 0.0005 0.005 0*0037 iLong Island 0.0006 0.0006 0.003 0.0028 beaver Creek 0.0006 0.0006 0.003 0.0023 .Laumptin 0.0006 0.009 0.0076 0.0007 * Analyst, W. H. ilnson ** Triplicate averages ** Chondrites average 6$ sulfide phase 82 .zr #&oates SET'sf Iicate Or. %zr a Ia cangas 0.0008 0.0006 0.003 0.0024 Estacado 0.0007 0.0006 0.003 0.0025 WarroatowA 0.0006 0.0000 0.003 0.0028 8.6 jL 2 am nO MISCN) Lamle rns a TE US IETIES "D MEORIES lCftr a- aad aOMW Rallaaite olivine n. detnatC4 n.deteted 0.005 Uhladnite, Johnstown 0.0014 0.0014 0.00 0.003 (0.001 ----W Carbonaceoas 0.0005 4 g ohondri te, Orgaeil Carbonaceous nodalo, Hessle TeWti te, Annaa, Indo China Teotite, North Cambodia, Indo China Tetiteo, 2.----- ------ ------ ----- e a 0.0009 - -0- 0.0004 fl 0-- 0.0004 a 0.00005 an tW O 0.003 0.020 0.020 -A g 0.020 So Sample. Z Z A SKARAARD ROQKS Descriltion tSo Averages r f *vragee 308 Acid granophyre 0.0002 0.015 359 uelanocratic acid granoptre 0.0002 0.050 1905 Basie hodenbergite granophyre 0 * 0015 0.024 414Z Feyalite ferro-gabbro 0.0010 0.006 1907 Rortonolite ferro- 0.0015 0.004 gabbro 3661 Gabbro without olivine 0.0023 0.008 4067 Olivine gabbro 0.0036 0.004 MISO)U4ANoUS Sample AMAWICS Deeeription r se rAe, Averages S-44 Anorthosite, Split Rook, Minn. Trage nadeteated S-49 Mica augite peridotite, Murfreseboro, Ark. 0*0009 0*040 Kimberlito, S. Arrica 0.0017 0.010 So-10 Lhersolito, Baltimore, Md. 0.0022 0.005 S-87 Pyroxenite, Webster,E.C. 0.0014 0.003 Satonite, RiddleOre. 0.0014 Trace ---- am <0.0000 >0.0001 *0* *TDPY . *4Tna T6Ct 200*0 9000*0 100*0 0o00*0 *0*N'aistq#, 's$aieqrns 6963 900*0 1100*0 M.,e& 'JgPAIRet petc,$es *u 1000*0 £00.0 0100 0 900*0 0100*0 900*0 9000*0 se'* SW~"O* ?40AOtQ *WTW9SJOC A **IP OUR RflUTIT gtit? *eZ*Tg '*uTrudaes .0 'n 'gaea 'dmj wstwg 'IetTrM IflW O$tlS-O I -I*ild 181C iilOliWi -. "0-1 -- 'I SIAVCr (19swzI Jo so5aYMIM tICJ Qtflt CHAPTER VI MIm;RALOGY It is most interesting to inquire Just how olosely the rooks from space which we call meteorites resemble the rooks on Earth. Since we are led in every approach to the belief that meteorites are fragments of a shattered planet, we are not surprised to find that meteorites are distinctly unlike the common rocks of the Earth's earface. for we believe that the outer craet of any planetary body, be it of gaseous, molten, or planetesimal origin, would have aiergone differentiation, and would be different from the deep-lying rocks of the planet's interior. Further, we may safely assume, and we are backed by a wealth of geologic (geophysical, geochemical, petrologic, and structural) data, that a planet's crast is thin, and that its total volume is extremely small compared to the total volume of the planet. ' hus from a shattered planet, relatively few of its Aragments would be from the crust, and we would be fortunate indeed to find on Earth such a meteorite. te have not yet been so fortunate. Howevor, the meteorites we know possess just those properties and characteristics we expect from geological investigation to exist in Earth's interior. geochemical facts and theory, stuaies of Seismic data, arth's magnetio 86 properties, studies of Larth'8 ellipticity of shape, and a score of other approaches point up the belief that iarth possesses a dense core surrounded by successive shells. ;%l- though it may be difficult to discover two geophysicist who agree on the nature of iEarth's interior, or to find one who knows with certainty its nature, it is safe to say that all geophysicists agree that iEarth possesses discontinaous shells -- that the barth is layered. Farther, we know the approxi- mate depths and thicknesses of these shells. So perhaps we may agree with Shand, who states (1949), "It is quite immaterial what view one holds regarding the origin of meteorites .... So whether one regards meteorites as shattered stars or shattered planets, nebular knots or condensed comets, as bolts from the Sun or as bombs from terrestrial volcanoes, the important fact for as is that meteorites blgj to in Me*ON our notice a tyoo of rook ~~ a that Wom I a d47fIf W6TaF"T*17iTe W ;and Jane; r orS tRI ihel T' r itT a th7 a ne0 "taer T0ilise pD6o sition ofo comlo tEI flaTrtT E "fl"E that petrology, geophysics and astronomy combine to indicate as likely to be found in the interior of the Larth." In general, the minerals of meteorites are similar and in most oases identical with ,*arth minerals. The minerals that are known to be exclusively meteoritic are becoming fewer and fewer (eaerburg, 1949). Of the several minerals that are uknown in tarth rooks, it is believed that we can explain their absence on accepted chemical laws. have been made artificially. Several 87 7nere are Listed in the following table the relative order of abundanae of Earth rooks and meteorites. Average Gristal Rock Feldopars Average Meteorite 59.5 Pyroxene and hornbleande 16.8 12.0 Olivine ) 25 Pyrozene ) 20 Mica Z8 Fe-Ni(Kamaoite & Tuenite) Troilite Others 7.9 Plagioclasee %AartE 15 ~ S < I Others The abawdance order for meteoritic minerals is the writer's own compilation and is at variance with the orders of mineral abandances usaal4 quoted. H. S. Washington (1939) lists the order of abuidanoes as nickel-iron, olivine rhombic pyroxene (eastatite, broazite, hyperathene), plagioolase (anorthite, labradorite, oligoolase) and maskelynite, based on compilations of Washington, G. 2. Merrill (1916), 0. C. Farrington (191b), and t. W. Cohen (1894). In all cases the mineral abandances have been based on the weight and/or numbers of meteorites in collections, rather than the proportion in which stony and iron meteorites strike Earth. * Clarke, F. ii., and washington, 14. 5., U.S.G.S. Prof. Peper 127. isrhaps the most strikind differences in meteoritic and terrestrial mineral abundanoes is the paucity of the feldspars, which comprise approximately 3/b of Larth rocks and are comparatively rare in meteorites. Furthermore, due to the Low amounts of 4 and Na in meteorites the potash and soda feldspare, orthoclase and microoline, are unknown in meteorites, except as traces by norm calculation. These minerals are unknown in modal analyses of meteorites, but are large in the bulk of Earth rooks. Of the plagioolasee, only the caloic ones are abundant in meteorites, and the sodic varieties are rarities. Another striking difference is the complete absence of the mioas and amphiboles in meteorites. This is due to the fact that water is entirely unknown in meteorites, and water is essential to the struotares of these minerals. Similarly, the common terrestrial mineral quartz is extremely rare and perhaps unknown in meteorites. In a few cases it has been reported in the superficial portions of a few iron meteorites, bat it ic mineral. ay not be an original meteorit- There have been a few reports of tridynite in stony meteorites. quarta would not be expected to ocour in material of the chemical composition of meteorites, for these rocks contain sauch a deficiency of silica that it all is used to form olivine and pyroxenes when the magma is cooling. F. G. Watson (1939) has made an exhaustive study of the falls of meteorites; that is, meteorites that have aotually been observed to strike the Larth and then collected, watson oonoluded that the ratio of stony meteorite falls to iron falls is about ten to one, However, assuming that stony meteorites are more likely to be shattered and lost by scattering in small pieces, he made a further study of the relative weights of irons and stones from falls. Than 39E stones yielded 7,705 kilograms, while 21 iron falls yielded 730 kilograms. The conclusion was that while the total material from stony falls is approximately ten times that from iron falls, the average iron yields nearly twice as much material as the average stone (Watson, 1945). Watson finally concluded that because there were so many uncertainties it was impossible to make an exact statement of the trae proportion of falling stone to iron, bat that the stj material is from foar to nine times as abuge ant as the metallic. It was on the basis of this conclasion that the preceeding table was compiled, in order to compare meteoritic mineral abundances with terrestrial abundances, with the assumption that stony material is from four to nine times as ubuadant as metallic. Meteoritic Minerals: 0. G. Farrington (1915) has al- ready adequately discussed the minerals of meteorites and their properties. The descriptions will not be repeated 90 here, a4d only those properties that are dermne to this deo8astson will be repeated. The followings Is the liet of aeteoritlo minerale Listed by ?arriagton. iJleme ate Orthoai Lioatee imetasliiates ineral CompositIca Olivi a (chrsolito ) inotatia forsterite stati to (Mg,Y. F Z4) 04 9g3104 MgS10 3 brenate (Mgtre 13W3g t6 M,Fe) (Si03)2 H persethone t4ltaeastatito CLinohyperatheam 9g 13103 (Mgo)(3103)2. (Mg, (SiO105 Aadite edonbergIte foltepare laeiooblses Maakte att (Oligooae Oxides LxS Cal glass) yiouJl2 ;Quarts (tentative only) Tridpnistotentative oay, MfenO U to Fe304 Chroeite Salti dos, Ehosaphids a Cabtesn Trollito FOS Oldhtmito CasY t4aabnelbU to Og t FeSr23 i Johriobersite Elements Other (Fenico)zP Uoheni to FogC On Oornite Oxysulfide of Ca and Ti Moissanite sic Sictel--iron Xamaoite Taenite 2tesgite FeNi Diamond Graphite(Cliftonite) 2hosphors (tentative) C C Weinbergerite (one ocoarreneoo) MAISLG & 3FeS8i03~ Rydrocarbone n(OxHyOz) Apatite Ca(F C1),Ca4 PONI Brewanerite (tentative) Lawrencite (Mg,Fe)C03 FecI 2 Minerals exclusively meteoritic: G. J. Neuerburg (1946, 1349), in a series of two papers has listed the minerals that are exol&sively meteoritic, and has discussed their occurrence and compiled an excellent bibliography. LNeuerburg lists the following minerals as exclusively meteoritics daubreelite, kosmochlor, merrillite, oldhamite, osbornite, schreibersite, weinbergerite, Oliaoeaatatite, and clinohypersthene. Reasons for including or excluding miner- als from the list are exhaustively documented by Neuerburg. Mineral descriptions: Kamacite, taenite, and plessite 92 are alloys with variable Fe-hi content. 5-6i nickel, cooasionally less. Laatcite contains Taenite contains 48% nickel. Plessite is not a mineral species at all, but is an intergrowth of kamacite and tasnite. Althouh terreutrial nickel. iron does not show identical crystal structares with meteoritic iron, it is now reognized that the crystal structure is a fanction of the mode of crystallization, rather Ahan a re- salt of composition (kohl and &erge, 1938). Clinoenstatite and clinohypersthene: A. N. Winchell (198) reports olinoenstatite in terrestrial rocks. hyperethene has been reported by E. Service (193) J. Verhoogen (1937). Clinoand by Enetatite and hyperathene ordinarily found in rocks are orthorhombic. S. 4. Shand (194 states that at high temperatures (114000 for U6=i05, below 9550C for varieties rich in FeSi%) they transotr varieties. into monoolinic Ferrosilite, FeSio%, is apperetitly unknown in the crystalline state. both olinoenstatite and clinohyperethene have been made synthetically (Allen, 4right, and Clement, 1906). by rapid cooling of a molten mass of pure magnesium silicate intergrowths of clinoentatite, similar to those foand in the Bishopville meteorite were formed. It was concaluded that the presence of such intergrowths in meteorites indicated rapid oooling. They further discovered that clinoenstatite trans- forms to the orthorhombio form at j3650Q, bat that this or- thorhombio form was "quite distinct from enstatite and uan- 93 known in nature". N. F. U. Henry, however, concluded that there was, with the exception of clinoferrosilite, no unquestionable ocaorrence of clino Mg-Fe pyroxenes. Neuerbarg,.in reviewing the papers of Winchell, Service, Henry, and Verhoogen concluded that with the possible exception of olinohyperethene cited by Verhooeen the terrestrial occurrence of clino Mg-re pyroxenes hns not been definitely established. Troilite: Though closely resembling each other, troll-. its and pyrrhbtite are now recognized as distinct mineral species. froilite more nearly approaches the composition FeS, while pyrrhotite approaches the composition Fe 11 S12 * Troilite is non-magnetic. A. 3. .akle (1922) describes an occurrence of troilite associated with magnetite in a sheured serpentine. The mode of origin he attributes to the hydrothermal alteration of magnetite. Certainly this mode of origin is different from that of meteoritio troilite. Neuerbarg suggests that the great abanidaace of free iron in meteorites may accoant for the formation of troilite. However, as pointed oat by Allen (1912), troilite probably should not be considered a separate mineral speoies, bat rather the "end point" of a solid solution series. O. C. Farrington (l916) states that "pyrrhotite (troilite)j, like impurities in artificial irons, tends to be most abundant sowards the periphery of a meteoritio individlal". This statement bears further verification, and, if true, would be most difficalt to explain on the basis of ta0 shattered planet hypothesis. ther study and verification tan However, without fur- writer is Uaable to comment on its significanco. oissanitez his exclusiveij meteoritic mineral, with the composition SiC, is, of course, eoommoonly known as the artifioial prodact carborwidam. L. . Chresohall and C.Milton (1931) reported finding moissanite in six examples of sedimnxtary rocks from the rooks. rdovician period to ecent Identification of the mineral by x.ray spectrography was unmistkable, These invstigators, after a critical examiation for sourSs of ountamination (pulverized samples and not thin sootions were used) conalwded that moissanite in sedimentary rooks either represeated meteoritic dust or was the indestruotable residue from fossil meteoriteo. ever, How- eaerbarg suggests that the "moissanite" reported was most likely a contamination dae to carborundam paste used in oleaning water taps, introduced when wasing the heavy mineral residues. Oldhamite: This mineral of the composition CaS would hardly be expected to ocoar in terrestrial rocks. but a strongq redaLuin oxidized to the sulfate. In any environment this salfide wouLd be However, the mineral gSalaband- 9b ite, occurs terrestrially but is unknown in meteorites. Laar (1897) reported CaS terrestrially, but Neuerburg be- lieves his evidence inconoluaive. Qebornite: This oompound (Tii) has been reported from blast £turnace saIas (Banaioter, 1941, find Stcry-Maakelyne, 1870). 4o0moehlor or Kosmohromit (A16 Fe4 Cri0 8 ); F. Las- peyree (1897) deseribtd this mineral from the Toluca iron. Subsequent mention was mnLade by Groth, Cohen, and Heintze (Neaerburg;, 1946). Lawreneite (Fe,ii)Cl : E. P. Henderson, in a person- al commnioation to feuerburg, reported lawrenoite doubtftlly in terrestrial irons from Greenland. Ferrous chloride, lacking, however, a nickel oontent, has been reported from Vesuvias (Yarrington, 1915). Although chlorine Is a common constitaent of lawrenoite in meteoritee (partioularly irons) flaorine has never been detected, althoah G. 2. Merrill made a careful eaarch for this element (1918). Cohenite (?eUi,0o30): as This minertl has been reported ucaurring in the terrestrial irons of Greenland (1944). It is identical with the artificial iron carbide cementite ocouring in steel. Uerrillite (Caaa22O9): G. J. Ueuerburg (1946) cites an extensive bibliography on the ocurrence of merrillite. Neuerbarg sugests that merrillite may not be a 96 a distinct mineral species, but rather mahy be a member of the complex apatite isomorphous series. Critical x-ray analy- sin is necesuary to establish its existence. Maskelynite: Tochermak (1872) first deseribed this min- eral from the Shergotty stone. It is believed to be a con- stituent of nearly all stony meteorites. In the Shergotty stone, which consisted of Wet maskelynite, the mineral ocour- red in feldspar-like laths, but lacked foldepathic cleavage. The composition was Si02 A12 03 G0 !a2O K20 56.3 25.7 11.6 5.1 1.3 100 Techermak regerded this mineral as a fused feldspar. However, Winchell (1897) found the mineral in the Fither mteorite amidst an isotopia material, portions of which resembled plagioolase. Winchell conoladed that the isotopio ater- ial was glsa from which the plagioolase had crystallized. The reverse view, however, is equally tenable: that the anisotropic plagiooleee is a devitrifioation prodact of an original glass that formed through too rapid cooling. The existence of maske4nite was also confirmed by A. ta Croix (1923) and G. k. Merrill (1918j. kerrill reported that the large proportion of stony meteorites contain a colorless, interstitial MAterial, which may be either isotropic or slightly doubly refracting, possessing a rather low index of refraotion which he designated as maskelynite. He noted that in all bat the Shergotty stone the glassy particles are of microscopic dimensions, defying separate ohemical analysis. In a study of the Holbrook stone (1912), Merrill 4etermined the refraction index to be 1.5, which, according to Larsen's tables, is that of oligoolase glass. Further stadies led Merrill to the conclusion that maselyAite may range in composition from oligoolaee to anorthite. Merrill attribates its glassy state to fusion since the original crystllization, "followed by a cooling which was too rapid to allow it to regain its normal properties". fraces of plagioolase twinning are occasionaliy present. This fact is interpreted by ferril to prove maskelynite a "refused feldspar, rather than a residual and original feldspathiO glass", confirming the inVestigations of Tahermak. It is farther pointed out that "an elevation in temperature sufficleat to fuse feldspar, without at least partial destraction of the olivine, would be impossible but in an atmosphere completely devoid of all oxidizing gases". However, the writer has observed in many thin sections of chodritic meteorites that ohondri are often composed largely of olivine and/or pyroxene glass, evincing destruction of olivine along with feldspar. In the case of the metallic salfides we may be sure that the atmosphere was reducing and under high pressure when and if the plagioclases and olivine were re-fased, for troilite diesociates at approximately 1150 0, fusion point of oligoolase, a temperature less than the 98 Farrington (I1lb) states that massieinite may be either an alteration proacut or way be of primary origiA. atzt Merrill's observations ox twinninj laeL.Le strongly suggeets the former, viz., by re-fusion. This fact mAust be taken strongly into account in theories of the uooling history of the shattered planet. Feldspar; 21aeioolaiss are Comon 1oatitaents of stony meteorites (they occuar also in Toluua iron in silicate inclasions), bat oomprise minor mineral peruentages in all bat the eakrites and howaritea. mon. northite is by far most o om- PLagioolaao rich meteorites exhibit ophitio flruoture, interpreted in terrestrial rooks as cryatallization o spur before pyroxene from a ailicate melt and ive of the maSmatic differentiation, Ohondritio plagioolaaso feld- ighly sagest- n. Michel (1914) foaud to be chiefly audio (oli600laae) while ekrites and howardites contain chiefly anorthite. arrington (l9lb) found feldspar as abundant in white ohondrites and nearly absent ln bluok ohondritea. The brecciated waoada stone, oonsisting of distinct light and dark fragments, shows this variation of plagloolaae content, as if the fragments were separate meteorites. iyroxnnos; stony meteorites. The pyroxenes are second only to olivine in Choadritia Stones, which comprise the balk of stony meteorites, have slight excessea of olivine over pyroxenes. Acnondritio eknkites and howardites, which most losely resemble certain terrestrial rooks, contain but little olivine and consist of ophitic intergrowths of anortiite and pyroxene and generally are aar4y metal and suafide free. $oMs achondrites, Etch as 4ishopville, consist almost untirely cf pyroxene. Bishopville consists of re- markably pare onstatite, with little free metal or ealflde. The orthorhombic pyroxenes are more abundant, bat an- like terrestrial rocks, munoolinio olinometatite-olinohypersthene is fairly common in meteorites. pyroxetnes, such as diopside, audlte, he Oa-Al-rich uedenbergite and pigs- onite are common meteoritic minerals, bat are chiefly restricted to the caloim-rich achondritee (containing anorthitoj, which are rare meteorite typea. A remarkable characteristic of the meteoritic enstatite-bronzite-hperethene series is that bronsite (14 - 15 F7O) is a rarity, whereas bronsite is common in the terrestrial series. In meteorites the change is abript from on- statite to hyperathene. or iron rich. These pyrozones are tither Mg-rich Intermediate brouite is rare. of this phenomenon is wanting. Prendel (189V) hxplanation found in the Grosaliebeathal stone enstatite and bronsite to characterize the chondri, while the groatSmass contained hypersthene. The Moore County, N. U. meteorite has recently been studied by E. P. Henderson and H. Tc. Davis (1936) and H. H. Hess and Henderson (1949). In bulk composition this meteor- - 100 it* resembles a Sudanry norite. These investigators dedaood that the variety of six pyroxene Phases present were probably derived from a single initial phase, tigeonite. Temperatur' of its original 4nVironmeUt was approximately 11360;, and Wthe uieeorite left this enviroament with tatastrophio saud- dsnness". The fabric is interpreted as sugestiag a primary layered developsent by orystal acoamaLation on the floor of a magma chamber - a crystal differentiation that ouotrrod in the original environment. xvi4enos for thia is that the py- roxene c axes and the plagioclase b &ad a axes tie in one Plana. Hess and Henderson point out that while pigeonite is rostricted in terrestrial 2oaks to rapidly cooled lavas or small hypabasal intrasions sad considered a metastable phase originating from rapid cooling, pigeonite alo oooars in rooks evincing intratellaric eystallisation, as at Mall, Sootland(Haflemond. 191). It is also a comon oonatituent of platonic rooks, but hero has altered on slow sooling to ortho-byperathene, containing !xMolt 001 aqgite plates in the planes parallel to of pigeonito Identical exsolation phenomaena of augito troa pigeonite ocar in the Moore County mteorite. This me-- teorite contains only about 10% hyperotheno, and susgests t o loe and )iendrsoa that cooling in the original environment 4id not prooeed to the extent for tho inversion pigeonito- I 101 hypersthene to occur. They attribute the 10% hyperathene present to inversion after it became ai meteorite. The most striking features c!f the plagioolase (bytowna it.) in the Moore County meteorite is the complete absence of zoning, indicating slow crystallization, and pronounoed linear orientation of its c-axes. Lack of cleavage in the plagioclase indicates a high-pressaure original environment. However, the pyroxenes have well-developed cleavage, which probably resulted from decrease of pressure when the planet was shattered. R. A. Daly (1938) believes that pyrozene cleavage could not exist at depths within the £arth greater than 40 kilometers because of escessive pressure. Ross and Henderson believe the temperature of the original environment to have been above 106500, the inversion temperature of pyroxene. Pressure could have inon aeed this temperature to 120000. These investigators, in this most interesting petrolo- gic study of a meteorite, conclude that it was derived from an Earth-sized planet, for the gravity field must have been sufficiently great to produce crystal settling, a condition a small planetoid-sized body could not fulfill. Becaus of more rapid cooling, a planet of smaller diameter than the "arth would not have sufficient time to differentiate a basaltic (nor granitio) crust. Thus, such meteorites may not exist. Anywati#-*#have found none. These observations sub- 102 stantiate the argumeats based on phase equilibria by Brown and Satterson, The rare meteorite mineral tridgmite ocoaz..r County meteorite. in the ak& The fact trat it did not invert to quartz (nor did the balk of the pigeoaite invert to orthorhombia forms) indicates sudden ohilling, an interraption we mnay possibly attribute to the shattering of the original planet into small fragments which would chill rapidly. Oliviae ate mineral. Olivine is the most abundant meteoritic siliOne meteorite, Chaeeigny, is composed almost entirely of olivine and is unique. Rammelsburg (1879) in a stuiy of cnondrites found the ratio of olivine to pyroxene to be V:8. Meteoritic olivine usually Ia Mg-rich, contain- ing from 10 - 15% fayalite molecule, and should be called onrysolite, according to the classifiaation of Wager and Deer (1939). Weinbergerite (3aAl04*3FeS0P: -. Berwerth (1906) desoribed the single ocarrence of this mineral, and from his analysis the proceeding chemical formula is taken. Berworth stated its orystal aystem to be orthorhombic. However, additional information is oertainly needed to establish the existence of taie unique mineral. Phosphoru: A single occurrence or native phosphorous has been desoribed by ?arrington (19@5). 3acrieberoite (Fei,Co)3P); Few, if any, minerals 103 found in meteorites nave -attracted as much attention as schriebersite. Great interest in this mineral was inspired by tne fact that a phosphide mineral of such oomposition would not *e expected as likely to occur in Earth orastal rooks, beoaase it would probably be oxidised to the phosphate. This fact is of particular interest in interpreting the origin of meteorites, for it suggests a strongly reducing environment. The calcium sulfide mineral, oldhamite, is in the same category of interest. Tornebohm (date unknown) re- ported sctriebersite from the Ovifak terrestrial Iron of Greenland, bat 0. C. Farrington considered his method of dotr44ation inoonclusive. 3ohreibersite has been prepared synthetioally. Diamond; The discovery of diamonds in the Canyon Dia- blo and Magara irons and in the Carcote and Nowo-Urei chondrites was of especial interest, leading koisan (1890, 1894) to his famoas successful experiments on prodacing artificial diamonds. Moissan'a method was to compress sugar charcoal in an iron cylinder sealed by an iron plug. this cylinder was then placed in a cruoible which oontained 200 grams of molten iron and placed in an electric furnace for further melting. On withdrawing, the crucible was rapidly cooled by immersion in molten lead (water was unsatisfactory, since it formed a badly conduoting layer of steam). Thus crystale of diamonds up to 0.5 mm were reported producea, which were re- 104 oovered by diasolvingj the iron in jala Moissan's experinento g suggeot a rapid cooling for me- teoric irons containing diunmoads. Eovver, the eperimente of Derge, IMehl, Bradley, and Baddhae suggont that Widmanstatten figureu require slow equilibrium conditions of cooling for tnis formation, indicating slow rather than rapid cooling for meteoritic iron. The Magura iron has an octahedral etcning figure, and the presence of this struactare with diamouds may perhaps appear inconsistent with Moissan's theory for rapid cooling. However, it is Cenerally .condeded by geologists that large diamonds require long periods of time for thir growth. Graphite: Graphite has been found in several irons, inoluding Magura (1.7 and graphite), Tolaea, Chulafinae, Maaapil (Farriagton, 191). Graphite is tsaally associated with troilite, either as intergrowths or inalasions. Far- rington quotes the origin atggested by J. Lawrence Smith that meteoritio graphite formed by action of 0 3z on inoandescent iron, and is in no way analogous to terrestrial graphite in origin. G. Ansdell and J. Dewar (1886) conolUted after oomparing many meteoritio and terrestrial graphites that they were similar in origin, and were formed by action of water and gases *a metal carbides. seems antenable, However, this view certainly The great balk of terrestrial graphite did not form in this manner, but occurs rather in crystalline 105 schists, contact metamorphic rooks, limestones, slates, and other rooks of sedimentary origin -- rooks in which we sure- l7 do not expect to find metallic earbides. Graphite in metamorphio aooks is believed to be derived from carbonaceous (organic) material originally deposited with the sediments. When graphite does occur in igneous rooks it is related to the pegmatites and hydrothermally altered rooas. However, it is sae to say that there is at present no evidence saggeating an organia origin for meteoritic carbon. Daubrei1te (YeCr 2i 4 ); Dabrelite is exclasively me- teoritic. It is an 4ncommon mineral usually associated with traflite. It is exluive to iron meteorites and is not known in the stones, Manier produced this mineral epithet- ically by heating an iron-ohromium alloy in an atmosphere of hydrogen sulfide. CHAPTER VII STRUCTURS AlD TEXTURSS OZ MToRITES kiatare of Chondrules; Among the most prominent physical featares of stony meteorites are small, rounded silicate grains kuowa as chondri or chondrales (diminutive), from the Greek word Xo vPog , or grain. Chondri occur in the complex metal, silicate sulfide matrix of silicate meteorites. They vary in thickness from approximately three centimeters to minute size. Their form is generally spherical, bat they may be oval or flattened, as if by deformation, or they may be most irregular in shape, as demonstrated in thin-section studies of this investigation. Like a common distingaishing feature between sandstones and qaartzites, chondritic meteorites may sometimes be broken around the chondri and sometimes through them. Thin section study reveals the chondri to be composed of a wide variety of minerals. Olivine and pyroxenes are most common, but augite chondri sometimes occur, and even plagioclase chondri have been reported by Lachermak in the stone of Dharmala. Glass is a common and probably universal constituent of chondritic meteorites. It occurs in a great variety of ways, such as matrix or groundmass material, substance of the chondri, and portions of mineral grains, as inclusions and intergrowths. Ieteoritic glass is usually brown, but may range from colorless to opaque-black. 107 The occarrence of glass is the result of rapid cooling of a silicate melt (or with remelting of crystals), and the analogy with glassy terrestrial rocks is extremely suggestive that cooling was too rapid to allow complete crystallization. Few, if any, ohondri are entirely crystalline. Glass is uasally conspioous, and forms a major portion of their substance. In gross structure ohondri resemble spheralites found in terrestrial voleanio rooks. However, thin section study re- veals invariably an ecentric radiating crystalline structure for chondri, whereas epheralites generally possess conoSn- trio radiating stractures. Explanation for this difference is still lacking. The crystalline minerals of chondri occur most commonly as radiating or porphyritic structures in a ground mass of glass. Frequently chondri possess a crystalline nucleas, which is surrounded by glass. observed. Network structures also are Chondri are most often light-colored, but may occasionally contain so many included grains of metal and troilite as to be black and nearly opaque in thin section. Chondri of a radiating structure are asaally composed of pyroxene (enstatite or hyperethene, rarely bronzite), while in those of porphyritio texture the insets are asaally olivine. Vorphrytio ohondri are usually predominantly glassy, while radiating structures approach more complete crystallization. 108 However, completely crystalline pyroxene chondri are anknown (Farrington, 1915). At common form of ohoadti is composed of both olivine and pyroxene. one Olivine uually ococars as insets in a groundmass of slaos and fibrous pyrox'Zither mineral ene. ay be in excess. The fibroas pyroxene- glass matrix indicates a later crystallization than the olivine insets, and is in keeping with the observations of Bowen and others on the order of orystallization of silicate Melts. We may safety assume that ohondri represent molten droplets that underwent rapid cooling. The ohondri may have solidified completely as glass and then have undergone slow reoryetallization in the solid state -- a process similar to the devitrifioation of glasses. However, chondri composed entirely of glass are known, in which no crystalline material is present. Such glassy ohondri indicate that devitrifica- tion, solid Qrystallization, was not the major process in the formation of ohondri. There is little reason to auppose that some ahondri ehoald have remained unchanged and completely glassy, while others devitrified almost completely to crystalline forms. A more likely explanation is that the molten, highly viscoua droplets underwent different rates of cooling, dependent apon their location in the planet's interior. Those near the surface cooled more rapidly and are more glassy, while the more crystalline forms represent slow cooling, deep-lying 109 material. Several other comoucnly £baerved feaWtres of chondri doserve mention, and us&y eveatually be of Use in solving the problem of the origin of' chodritic teztures. Chondri of a wide varioty of rlneralogio compositions and physical straotures are Common4 Closely associated in any chondritio me- teorite. within the same thin section =,y be observed rounded ohondri, possessing both radtttiat and porphyritic texture, fibroas and network text4ree, Olivine onondri ocoar intimate- ly associated with those of pyroxene chondri, mixed mineral ohondri, or glassy ohondri. Tschermak has described from the Daarmsala stone a large porphritic chondras completely enolosing a smaller ohondras. A photograph of this phenomenon is shown in Farriugton's Meteorites, on page 106. Chondri which have een feagmented sometimes oacur, as in the Mezo Madaras stone described by Tschermak. The sepa- rate fragments of a single chondras may rarely be aisoovered in Jzxtaposition. dhatever prodaced the fragmentation sepa- rated the fragments, This could be oauased either by explos- ive activity or by violent movement in a viscoas, partly crystalline matrix. chondri. Specimnas frequently ocur with whole The fragmentation process mast not have been too violent. If we coald but understand the origin of the ohondri we 110 would no doubt be well along in our understanding of conditions within the former planet. However, immense inconsist- enoes confront us in oar investigation. That stony meteorites are fragmental in nature is strongly suggested by the The fragmental nature of such meteorites as the ahondrites. Camberland Falls stone (U.S. National Museum) is hardly contestable. This stone has a marked brecoiated and fragmental structure, being composed of large angular black fragments imbedded in a white matrix, We mast know not only how chondti formed, bat how they have come to occupy their present positions. Certainly they underwent fragmentation after solidification, as a thin sotion study of the Mezo adaras stone (see picture in Farring- ton's Meteorites, pg. 190) and many others will attest. Various oridin theories have been proposed, of which several will be reviewed. G. 2. Merrill (1920) regards ahondri as "rook fragments reduaed to their present form through mechanical attrition". Farther, Merrill states, "In brief, their present structural pecularities, both external and internal, are entirely inconsistent with any conceivable theory of origin bat that of detrital particles from solidified magmas." However, the occurrence of ohondri completely enclosed within chondri, as in the aforementioned-Sharmsala stone, seemingly makes this explanation untenable. Attrition, the abrasion by rubbing together of fragments, cannot account 111 for the inolasion of one choandras within another. F. G. Watson (1943) notes the strikingly fragmental nature of the Sharps Meteorite and asserts that the ohondri and fragments are "so distributed about the larger ones as to afford nmistakable evidence of mechanical attrition." It seems to the present writer that, though evidence of mechanical attrition is unmistakable in stony meteorites, this process cannot account for the formation of chondri. After formation the ohondri were undoubtedly modified in shape by attrition and often fractured. The breociated character of a large portion of stony meteorites is unmistakable and must be taken into account in any theory of origin. Their resemblance to agglomeritio, tuffaceous volcanio rooks is striking. Several investigators have suggested that ehondrules represent molten droplets blown explosively from the surface of the former planet. In falling, these drops cooled and assumed spherical shapes. If this hypothesis is true we are forced to admit that originally the chondri solidified wholly as glasses and that the crystaltine structures we now observe are the result of devitrification. Where is, however, a strong argament against this origin for the ohondrales, This mode of origin suggests that the chondri should be confined to a thin surface shell of relatively small volume, bat we know that fully 90% of the stony 112 meteorites are chondrites. They possess ahondri. Chondrites, therefore, must represent the major portion of the total volume of the shattered planet. salt of surface explosions, Thas, they are not the re- Solely as a working hypothesis the writer presents the following. Fissares connecting with the deep interior of the planet could conduct molten material explosively to the surface, where it would be ejected and rained back to the surface as fragments, ashes, and chondri. If this process were continuing, each new surface would be saccessively baried under new explosive material, becoming more and more deeply buried. It is barely conceivable that ultimately the whole silicate shell of the planet could be reworked from deep interior to surface. In such a manner the chondri could be distributed throughout the silicate shells surrounding the core. Evidence of mechanical movement within the solidified meteoritic material is abundant, e.g., the frequent brecciated structure of stony meteorites, and the occurrences of faults, slickensides and polished surfaces. S. Meunier made an interesting study (1873) of the mineralogical and stractaral similarities of meteorites and terrestrial rocks. He classified rocks and their meteoritio analogs as 1) Normal; Z) Brocciated; 3) Metamorphio; 4) Eraptive; 5) rooks traversed with veins (filonniennes concrstionnees); and 6) Volcanic. Veinas in both rocks and meteorites he regarded as fracture 113 fillings. He pointed oat that Just as faults in terrestrial rooks may be detected by the amount of throw of the rooks constituting their two sides, so can the faults of meteorites. Many Otony meteorites exhibit apparently true faults, with demonstrable throws and polished surfaces. For example, the stone of Aamieres, described by Meunier, exhibits a fault out by another, with a downthrow of several centimeters. This remarkable stone (and many others) exhibits the property of turning black when heated. The material adjacent to the fault surfaces in this meteorite has been altered from grey to black, presumably by heat of friction due to fault movements. When the throw is greatest, the blackening has ex- tended the farthest from the fault surface. Thus we have an effective and sensitive thermometer, with which we can conceivably measure the dynamic energy that accompanied this cosmological faulting and illuminate oar knowledge of the conditions in the former planet's interior. G. Tschermak (1878) in a study of the Groenja stone, as well as others, made matny interesting observations on the nature of chondri. He noted the occurrence of a crust fre~ quently surrounding chondri, especially over those composed of bronzite which possess fibrous structure, The crust is likewise fibrous and is optically orientated like the enclosed silicate. Tschermak suggests that this crust has been "pro- ducoed by some agent acting from without, perhaps heat in con- 114 Junction with a reducing gas" (quoted from -. Flight, 1887). This agent has not caused fusion, bat only a textural modification of the surface mterial. The present writer finds it difficult to picture the role of a "reducing gas". The second important observation of Tachermak is the distribution into zones of "magnetic pyrite"(troilite?) in many of the granular inclosed masses, Refloted light studies of chondri in thin section revealed sometimes a metallic sulfide crust to the ohondri, and sometimes the metallic sulfide occupied the center of the ohondrus. In all asses, the metallic sulfide in- clusions apparently occupy the interstices, as if had "impregnated the rocky mass". the sulfide The metallic sulfide is always absent from the crystalline insets, and Tuchermak belicves the impregnation to have ocourred after the insets took their present shapes, i.e., after their orystallization within the glassy matrix, and to have occurred when the whole taffaeouw mass was strongly heated. Tschermak assumes that the fractured crystalline and glasay material of the ohondri drew the molten metallic sulfides into fractures and cavities, The writer suggests that the metallic sulfide arose as an immiscible phase. It probably was already present. As the temperature fell in the silicate mix, globales of immiscible metal and sulfide phases separated. The melt cooled rapidly, permitting only a partial crystallization of silicate minerals in a glassy matrix. Cooling oaused contraction of the glass 115 and the crystals and produoed fractures which were intimately filled by the metallio and sulfide phases present. High pres- sareuat be assumed and is certainly expected, in order that the sulfide phase would not dissociate, for troilite completely disaooiates at approximately 115000 under atmospheric conditions. Tochermak concladed his study with the hypothesis that there were two distinct stages in the formation of chondri. First the olivinous taff was produced by fracturing and at. trition, whereby the tougher particles were rolled and rubbed together until they had rounded or spherical forms. Second, the material was strongly reheated (though not to the melting point of silicates, bat only to the melting point of salfides) and the surfaces of the ohondri were modified by the "redacing action of gases and vapors". That the iron inclusions in chondri could have been derived directly from the siliceos melt as an immiscible pro- dact receives direct support from the work of N. L. 13owen and J. F. 3ohairer (1932), who have shown this system to melt incongruously, with separation of iron. In a study of the Rangala meteorite J. A. Dunn (1939) made interesting observations on the dissooiation of troilite as observed in the crusts of meteorites. 7e assumed (correct- ly) that the velocity of a meteorite would decrease due to air resistane as it fell to Larth, and that as a consequence 116 the surface temperature generated by friction would be progressively diminished. He observed that the first change in troilite occurred at the base of the cruet, with lose of sulfur, accompanied by the appearance of "exeolation droplets of iron". surface, Under great heat, that is, nearer the the molten sulfide streamed out through fractures, and remained as veinlets of troilite and iron. He further disassed the matter of development of iron from the troilite as to whether it resulted from simple dissociation or whether the sulfur was burnt off as 30, oxygen. due to atmospheric Hematite (?) was developed in the "slag selvage", suggesting the possibility that SOg was formed, but he farther pointed oat that it is difficult to conceive how oxygen ooald have been absorbed down to the inner zone of the crust against the opposing stream of outwardly dissipating S and Fe vapor. Dunn concluded from his study of crustal veins and veins within the body of the meteorite that the latter veins were already present when the meteorite entered Earth's atmosphere. There is no parallel between the arrangement of troilite, kamaoite and taenite in the crastal veins and in the interior veins. The metallic constituents of the interior veins were solid and in place when the meteorite entered the E'arth's atmosphere. Veins in meteorites differ in aenoral from veins in ter- 117 restrial rooks in that the vein material of meteorites is essentially of the same material as the material of which the Farrington concludes that thejmaterial meteorite is composed. has not beer injected, but has been altered in place and states that some of the broader veins show a distinct flow structure, He concludes that veins are oaased by "penetra- tion of heat into the fissares of the meteorite during its passage through the atmosphere", and discards the theory that the veins are of preterrestrial origin. However, there seem to be both inconsistency and error in Farrington's conclusion here, are known to be cold. The interiors of meteorites Heat cannot be conducted to the me- teorite's interior as fast as it is generated and stripped away from the surface. Thus the flow structure in veins could not have been produced during the meteorite's flight through Earth's atmosphere, bat more likely was produced by the heat of friction caused by movement along the fault plane. Expersiental evidence is abundant, and almost incon- testable, that blackening of the chondritio material may be caused by heating alone. In the writer's preparation of ohondritic meteorites for spectrographic arcing the material was first heated in a blast flame in order to dissociate the sulfides present and to convert them to oxides, so that they woulc not explode from the eleotrod~e crater ou arcing. In a reducing flame the 118 material would blacken, whereas tnder oxidizinc conditions the sulfides would be converted to iron oxides with characteristic reddish color. It is con laded that cholcritic tacttor- ites may be blackened by heat alone. Ir conclasion, it may be said that the faulted veins of meteorites, their brecciated condition, and the almost invariable ocoarrence of fragmented ehondri and other mineral grains indicate that forces have operated that are entirely inconsietent with forces that could occur in a small body. mast have been of planetary size. The body Baer (1949) interprets the elastic struatare as the reeult of "the breaking up of incipient crystallization by convection currente duringz. eolidification of a parent-sized planet". Olivine is the most abundant silicate mineral in chondritio meteorites. However, pyrozene is present asally in almost equal amoants. It is of significance that meteoritic olivine is aeally mnagnesium rich, containing from 10-1b% of the fayalite molecule. Aoording to the equilibrium diagram of Bowen and Schairer (195), olivine of this composition would have crystallized from a melt at temperatures ranging from 1650 0 to 1760 0C. C a iron-enriched silicate residae would remain. If cooling had proceeded out of equilibrium, this ironenriched residue would solidify as a laus. In thin section almost all olivine grains are observed to be surrounded by, imbedded in, or interspersed with dark brown silicate glass. 119 However, we are always faced with the posadbility that all the silicate may have solidified as glass, and that the Orystale present represent a devitrification product; i.e., arza- tallization from the solid, amorphoas state. 2xperimental work on the devitrification process in mineral glasses is needed to solve this problem. It is here suggoeted that according to the chemical law of LeChatelier devitrifioation under hig resre generally be favored for silicate mineral glasses. would In the following table are aaown the specifUic gravities of several silicate minerals which occur in meteorites and the corrnsponding valaes for their glasses. Cooling in an tarth-sized planetary body would initialls be rapid. The rate of cooling would increase with de- creasing planet size. life would be short. fell. If a molten crust should exist, its Cooling would slow as the temperature Small planets (spheres) cool more rapidly than large planets, due to the greater surface area compared to their masU. Initial cooling is rapid in a molten planetary body due to convection currents in the high4 fluid interior conveying heat to the surface, where it is radiated into space. Rapid initial cooling would favor vitrification of silicates. The slower cooling that followed would allow time in which the ions of the silicate glass could rearrange in crystal structures. Assuming a temperature of 1000'-- 15000C, a 120 Mineral Olivia Anorthite Sp. G. Glass 0.381 2.831 16.3 3.175 4.743 13. 6 2. 765 2.700 2.4 R. A. Daly, p. $ decrease Sp. G. ry a tal Cry s ta l Sp. 0. Gla ss Igneoums Rooks and the Deptaof the Earth, 50, McGraw-Hill, 1933. 121 temperatu~re at which the refractory silicates could exist in the solid state, thia high temperaturo would greatly favor the ionic migrations noceeary to form crystal structures. Because in the planet's interior there would exist hifh preasures, the silicate chemical system would tend (by Le Chatela's lawj towards a state of minimum volume. This state, in the case of silicates, is the cryatalline state. Since none of the meteorites we possess are extraordinarily porous, this adjustment to lesser volume mast result in a decrease in the planet's diameter. This decrease in volume would partly be accomplished by solid flow of the glasses and crystals present, then violent movement, of the natare of fracturing, faulting, and breociation would occur. The almost aivereal brecciated strcture of meteorites, their fraotures and faults, attest that such movements ocarred. The inward, contracting forces of the silicate shells woald be opposed by an outward force of the expanding nickeliron core, for this alloy, like water, expands on solidification. uhether or not the total planet increased or decreased in volume would depend, of coarse, on the relative sizes of cores and shells, of which there is at present no sure knowledge. ie can only conjecture that interior adjtstmente in volume would be expressed on the planetts crust in auch phenomena as mountain-building, faultinc, possibly valcanism, I-, 122 and other pheaomena, Bat whatever the surface resflte, or the total change in volume, we may safe4y assume that the solid mater14l of the planet's interior would flow, and be fratured, faULte&, and brecaiated. If such forces are at present operating in the interior of the Earth, here is a possible eowroe for the forces which build mountains. CHAPTER VIII SAT EDPATH ?OTHSIS A wide number of independent approcches have almost invariably led to and confirmed the belief that meteorites are ,the remaants of one or more shattered planets, C. A. Bauer (1949) has made an admirable argument for this theory. Also, F. G. Wateon (1938) has contributed many argaments in its favor. The argamoats presented by baaer ani fatson are in- oorporated in this chapter. Their astronomical arguments are given in full or in part, withoat major discussion here. It is hoped that the geological ideas of the writer will enhance the theory and add some bit to our knowledge of the meteorites, Earth's interior, and the origin of the Solar System. Perhaps the final solation to the problem of the origin of the Solar System may best be reached through this analytical approach. Following ic presented a list of facts and observations which all point to the plausibility of the shattered planet hypothesis. It is hoped that this presentation will raise the hypottesis to the statme of taeory. Astronomieal 1. Association of meteorites with planetoids (aster- oids) (and non-association with oomets). 2. Roohe's limit -- a case for shattering. 124 Geological l. The meteoritic sequenoe. 2. GeocahemiCal and petrological evidence. 6. Struoture oZ pallasites. 4. Geochemical equilibria. b. The widmanstatten figares, suggesting a slowly cooling planetary oore -- 6. solid on disruption. Structures: brecciation, chondrales, fractures cnd. faults. Astronomical Evidence AasoMiation or meteors with comets: A great stride forward had been made in our understanding of meteorites when it was recognised that meteors and meteorites are separate phenomena. The distinction was difficult to make, for botn manifest similar appearance as they streak through Earta's atSosphore. The distinction was made chiefly through discovery of the facts that no meteorite ?ws ever been associated with a meteor snower radiant, and that the meteor showers are assoe eiated with -- are, in tact, derived from oomets. Shower me- tecrb are tiny particles, too small to sarvive their journey throug Iatth's atmosphere. Meteoritea are larger fragments, pro'bably elfleding three kilograms when they enter Earth's atmos phere. Astronomers have long argaed the existence of interstel- 125 Opinion has nwaag widely for and against such lar meteorites. visitors. H. A. Newton (4.) conoluded from a study of 116 falls on which data was then available that 109 had orbits witain the Solar System, had direct motion, and nad orbits of Opi low inclination. (1933), in studies of orbits of me- teors concluded that a high peroentage had hyperbolio orbits and thas were visitors from interstellar apace. However, the writer was told by Professor F. L. whipple, of Harvard Observatory, that in the early 1930's many as- tronomers strongly believed in meteors with hyperbolia orbits, bat that photographic meteor research has steadily ahaten this view, and now an upper limit of 2 or 3% may be set on possible nyperbolic meteors; furthermore, that the chances of this apper limit being too small are becoming inIt is safe to say that the grest majority oreasingly less. of mateork Are members of the Solar System, and until evidenSe to she contrary is presented, meteorites may likewise be so considered. The observational data of known falls strongly suggests that meteorites are in orbits about the Sun, and that their orbital elements closely resemble those of a large number of asteroids that olosely approach Earth (Baaer, 1949). The majority appear to have direct motion about the San. Planetoids lie in a breed belt about the SuAn, in orbits aeaally confined between the orbit of Jupiter and that of Mars. 126 Kepler had suggested the existence of eUh a planet. The Titius-Bode law may be expressed mathematically as rn= a+b*2Z, where r is the distance of the nth planet from the Sun, and a and b are constants. This law prediated the distances of the planets from the Suan. To the early 18th century astronomers, its otherwise near infallibility strontlg suggested that a small planet existed between the orbits of aars and Jupiter. They were led to a dtligsnt search of the heaven& which resulted in the discovery in 1801 of the asteroid Cores by 2iazzi. Discovery of these small planetary bodies hue continued until at present more than 1500 are known. All are small in size. Vesta, the largest, is less than 400 kilometers (air. 240 miles) in diameter (or greatest thickness, ;Aeverrier, in a study of the motion of the line of apsides of the orbit of Mare, coaladed that the total aggregate mass of the planetoids could not exceed one-fourth that of Earth, Assuming a mean density of that of Mars for the plan- etoids, their total volume would equal that of a planet approximately 8000 kilometers in diameter. Photometric studies of the planetoids have revealed that most are variable. This phenomenon can be interpreted either as du# to materials of different retleoting power on different parts of a planetoid, or as dae tofdd shapes. As there is no reason to suppose that planetoids are composed of differ- 127 Oet materials on their opposite sides, the second hypothesis is more tenable. For, if the planotoids were fragmental in shape, the areas of their reflooting surfaces presented to Earth would vary (if they rotated or if not). This variabil- ity in the light from planetoids stronly suggests that they are fragments and not spherioal bodies. We know from the odd shapes of meteorites (Farrington, 1915) that they were fragmental too before their entry into $arth't atmosphere. R,0oe limit: The fragmental shape of both planetoids and meteorites suggests explosive shattering or collision as a mode of origin, and strongly negates any ideas as to oondensatory or aceretionary origin for either. An argument is here presented that the planetoids did not result from explosion. An explosion from within a planet, if violent enough to erapt a planet 8000 kilometers in diameter, would probably produce a large quantity of finely pulverized material. A series of fragmental sizes, contin- uouas down to minute particles or dust should be prodaoed. It is well known that saceossive division of any mass incresses its total surface area. Calculations will show that fine dust from a palverised planet of such size would have sufficient surface area to be visible from Earth as a glow, similar to the Zodiacal light and Gegenschein (which arise from reflection from particles between Earth and Suan). Such a glow is not observed in the planetoid belt. Perhaps we ean safely assue that the planetoids do not diminish in size beyond a certain limit. This limit ia set by the miner- al grains and glassy entities of which the planetoids (meo teorites?) are composed. It is aujgested that tidal disruption would be zuoh loen violent than an internal explosion. hoohe proved (18f1) that if two homogeneous liquid spheres of planetary (or stellar) size approachod within 2.46 radiI of the argor, primary body, the smaller sphere would be dierupted b- tiaal foraes. G. H, Darwin elaborated thia theory. Although Roooe's limit theory applied to homogonoois, liquid spheres (atellites), non-homogeneous, we ay with safety apply it solid spheres. to The same tidal forces would exist, but undoubtedly the limit at which disruption would occur would be greater. ither a liquid or a solid sphere 'would be distorted (as Earth is by tides) into an ellipsoidal shape. When the cohesive forces between the solid (min- eral) grains of the smaller sphere were exceeded, tidal disraption would ocar. This tidal disruption would be less violent than disruption from internal explosion. Violent ezploeion would ejeot fragments randomly with no preferred orbital orientation about the Sun, On the other hand, the less violent fli dal disruption would tend to leave the fragments in the original orbit the smaller planet was pursuing before its die- 129 raption, That this mode of shattering is bat theoretical is admitted, bat we may point, for example, to the rings and satelittes of Saturn. The rings, which lork Maxwell in 1859 proved to be composed of small fragments, lie just within Roche's limit, while the first satellite lies jast withoat. The first moon of Uranas lies just outside Roche's limit, and some astronomers predict that in the future it will spiral inward until it reaches the point of disruption. Then, like Saturn, Uranas will possoes a ringL Fragmentaa ea ea: That meteorites are fragmental and most irregalar in shape as they enter Barth's atmosphere from space is attested by their fragmental shapes when collooted. 0. G. Farrington (1915) has given an excellent classification of meteorite shapes and the extent to which burning in the atmosphere altered their original shapes. The facts and argumente need not be repeated hero. it SUffice to say that their present shapes attest the fact of their pro-atmospheric fragmental shapes, and that few, if any, were spherical. The fragmental shape of meteorites is in line with the above cited evidence that the planetoids are irregalar in shape and are likewise fragments. Efforts have been made by astronomers to determine the sabstance or which the planetoids are made by the nature of their reflooted light. F. G. Watson (1939) concludes that 130 from reflected light alone we cannot tell the nature of the planetoids, even to the extent of whether they have metallic or stony surfaces. feolocal MEtiO *A qenOO: vidence 0. G. Farrington discovered the relationship in iron meteorites that with the decrease of iron content (increase of Ni) the width of kaoscite lammellao decreased; thas the iron meteorites coald be arranged in sequenoe. In the light of our knowledge of ex-solution phenomena in cooling of alloys, this discovery suggests that the continuoas variation in width of the kamasoite lamellae is a result of progressive cooling rates. This observ- ation may be interpreted that the metallic meteorites originated in the core of a planet. As the planet cooled, center of the core would be the last to solidify -- the the near- er to the surface, the faster would be the cooling rate, thus producing the variation in widths of kamaoite lamellae. 0. A. Baaer (1949) extended this knowledge by comparison wita our seismic knowledge of Earth's interior. It is pointed out that a mrked discontinaity exists in tarth at a distance 0.b5 of its radias from center. Likewise the meteor- itic seqaene from irons to pallasites is rather abrapt. Iron meteorites average about 7.5 in specific gravity, while pallasites average about 4.2 and intermediate varieties are unknown. Thus it is indicated that in the shattered planet there 131 existed a discontinuity analogous to that in Earth. Because we do not know the true relative abundances of stones to irons we can not know the size of the planet's core. Watson concluded that the ratio of atones to irons by weight was within the limits of four to nine stones to one iron, and was unable to fix a more precise ratio. Bauer (1949) However, obtained a value of 0.45 of the radiom as the planet core size, on the assumption that Watson's studies were correot. Bat Watson did not fix the ratio of stones to irons except as a lower limit of 4:1 and an apper of 9:1. Thus Bauer's value is not acceptable on the assamption made. Using *atson's ratios of stones to irons of 4:1 and 9:1, and assuming a specific gravity of 7.5 for the core and 4 for the silicate shell, a minimum value of 0.36 of the planet's radian is obtained and a maximum of 0.62, the mean value of which is 0.48, about 0.45, which is saser's value, However, we have only observational data (Watson's compilation) allowing us to set an upper and lower limit, and we are still left not knowing whether the core of the shattered planet was larger or smaller than £arth's core (0.55 of radias), except that the mean from our observational data indicates a lesser site. Jeffreys (1924) concludes that the smaller a planet is the smaller its core. His studies were based on the ellip- tioity of the shapes of Earth and Mars, for ellipticity is a 132 function of mean density, rotation period, and the increase in density towards center. Unfortunately the elliptioity of Venus and Mercury is not known, to extend this hypothesis, but we may suppose from their known volumes and masses that their cores are relatively smaller than that of Earth. Geochemical and pe trological evidence; A. F. Badding. ton (1943) has made a number of interesting dedactions on the arth model from meteorite data. He found that as oli- vine increases in quantity the olivine is richer in fayalite, Variation is from Fogo to 7063, and he observed that this variation is the opposite to that found in terrestrial stratiform sheets. Furthermore, the near oonstancy (air. 5%) of troilite in ohondritic meteorites indicates to baddington and Chirvineky that this mineral was not differentiated by fractional crys.tallization and settling of crystals. A feasible ex- planation is that convection currents prevented settling of the heavier components, although the gravity field intensity was sufficient to have caused it. A final observation was that the pyroxenes became more magnesium-riah the greater the amount of pyroxene, This trend is in harmony with fractional crystallization in terrestrial stratiform sheets. The constancy of troilite and the variation of olivine composition make the hypothesis of simple crystal fractiona- 133 tion in the former planet untenable. However, it should here be pointed out that simple crystal fractionation has apparently rarely occurred in 2karth stratiform sheets, as the numerous inconsistencies in applying this process alone attest. Hess and Henderson, as noted in Chapter VI, have shown that in at least one shell of the planet, that from which the Moore County stone came, crystal fractionation may nave occarred to give the observed preferred orientation to the feldspar and pyroxene crystals. A. E. Nordenekiold (1878) and W. wahl (1910) showed that for several ohondritic meteorites the atomic composition is very uimilar, and conoluded that the difference between the enstatite-rich Daniel's Kial (Hvittis) stone and other (more FeO-rich) ohondrites 4#gaonong an Q W. Flight amount of jggen t stones contain. the dif- (1881-82) showed that if the ohondrites are arranged in order of increasing free metal phase content, then the Ni content of the free metal decreases. G. T. Prior (1916), after making a systematic study of chondrites, stated that "the lees the amount of Ni-Fe in ahondrites, the richer the metal phase is in Ni and the richer in Fe are the Mg silicates". He farther pointed out that the total ratio of Fe atoms to Mg atoms varies but little; 1.0 for Daniel's Kial (25 Soka Banja (4% free metal). free metal) and 1.8 for Thus for all chondritio meteor- 134 ites the percentage of MgO varies only within narrow limits. The meteoritic sequence is remarkably continuoas for stony meteorites, with nearly all proportions from metal free to metal rich specimens in our collection. This remarkable relationship *rw be observed most strikingly in the spectra of meteorites, as in the twenty- one chondritic spectra of this investigation. In fact, the most striking feature of analytioal studies of these spectra is their almost identical appearanos, any one spectra being unidentifiable from any other, and the trace elements being present in almost constant amounts. The saggestion is strong that all chondrites had a similar origin, possibly within a planet-sised body. Wahl and Prior both attributed these remarkable relationships of Ni, Fe, Ig0, and FeO to the results of oxidation. Prior oonluAed that "all meteorites have had a common origin from a single magma, which is most nearly representad by that which gave rise to the Bastes and Daniel's Kial (Rittis) types of meteoritic stones, and that from this magma all other types have been prodtsed by progressive oxidation of the nickelferoas iron." Prior states that in the Daniel's Kial magma only outficient oxygen was present to react with Si, Mg, Al, and Na (and to a slight extent with Ca and Or), but that scarcely any reacted with Fe, because there was not enough oxygen present. 135 In other environments, presamably in other shelle of the planet, when the magmas enoountered more oxidizing agents (&ore oxygen) the iron would be progressively oxidized; part of the Mg-llioate (enstatite) would be reduced to ferriferous olivine and part to bronsite. In all of these re- actions 1i took no part, bat remained and became enriched in the free metal phase. 'W.Wahl (1910) explained the non- reactivity of i as duo to the lower heat of production of NiO as compared with that of 7.0. Wahl suggested that ohondritic stones were produced unAer surface conditions like volcanic tuffs, and stated "that it may be that the oxidation of bronaite i-4e with resultant prodaction of olivine and was of sach violent nature that drops were thrown out (tae ohondri) in a hot and ratified atmosphere (as sug- gested by L. H. borgetrom, Da motiorit von S. Michl, Ball. Comm. Geol. Fialande, No. 34, 38, 1912) and oonsolidated suftioiently slowly to form the crystalline chondrules". The ditficulty of this argamsnt for the surface origin of ohondri, on the basis of the predominance of chondritic material (at least 76% of the total volae of meteorites) has been diecussed in the chapter on the mineralogy of meteorites, this thesis, and a theory proposed to explain the great paradox -- that tUe great volume of meteorites resemble volcanio agglomNote: "Hyperstheae" would be more correct here than "bronsite", for bronaite of intermediate Fe content, compared to enstatite and hyperathene, is remarkably rare in meteorites. * 136 critic material and appear to result from sarface phenomena. H. Brown and G. Sattersoan (1947) extended the work of previous investigators and made several important further observations listed below: l. The average Bi content of the metal phase of stony meteorites is greater than the average Ni content of iron meteorites. 2. The average Co content of the metal phase of stony meteorites is greater than the average Go content of iron meteorites. 3. Graphical spreads of the Fe, AL, Co is greater in the metal pase of stony meteorites than in iron meteorites. Prior postulated that the achondrites represented a higher stage of oxidization than the chondrites, and average much higher in AlgO 3 and CaO, bat are poorer in sulfides and free metal. Badaington (1943) oonsiders Prior's theory of progressive oxidization adequate for the ohondrites but not for the achondrites. baddington points oat that there is a striking contrast in the mode of variation of the composition between the chondritio and aehondritic meteorites. The Ohon- drites may fit the theory of progressive oxidization of a primary magma, but the achondrites are better explained on the basis of fractional crystallization. In conclusion, our present state of knowledge indicates 137 that in the planetary body in which the meteorites originated several processes of magmatic differentiation operated. In te shell of the planet, wherein the ohondrites were formed, the progressive oxidation of a primary magma seems to be the most plausible hypothesis. However, the ahondritic strao- tare of these meteorites has get to be explLAned. Evidenoe points to the belief that within the aohondritic shell fractional orystallization was the dominant differentiating process. Natare of pallasites: The problem of the origin of the pallasites (meteorites composed of a continuous mesh of i- Fe phase inclosing olivine) has interested many investigatore. It can be concluded at once that the environment in which pallasites orytallized was deficient in oxygen and that a limited amount of silicon was present. The shapes of the olivine crystals mast be explained in a theory of origin, for they are rounded or fragmented, as if produced or modified by attrition. R. a. 'Dalg (1945) argad that all of the meteorites originated from the fragmentation of a single planet, and that the pallasites were the result of gravitational settling within this planet, The meteorite Itsawisis has unfratured olivine crystale enclosing metallic particles, demonstrating that metal was present before crystallization of the olivine. 138 Merrill (1930) concluded that the metal phase of meteorites (and pallasites) wra derived from ferrous chloride, which was originally introduced at a temperature lower than the melting point of the silicates, and was then redaced, He interpreted the small amounts of laiwrencite found in mete allio meteorites as unreduced residue. Lord Rayleigh (1942,1944) attempted, with quite good success, to reprodaos the struActares of chondrites. He ae- samed that pallasites originated by olivine weathering out of rocks, which became immersed in molten iron and were He prodaed artificial pallasite rounded by attrition. structares by pouring molten solder over fragments of stoatits and thas produced the shapes of olivine orystals in pallasitee. He concluded that pallasites did not originate from free metal separating out of a silicate malt. However, the olivine crystals of the Itsawisis meteorite, and the e- periments of Bowen and Shairer, both evince that metal would separate from a Fe, Mg, Ni-silioate melt, containing a saperabundance of Fe and i. H. J. Sel (1949) has contributed mouch to our knowledge of pallasites and their origin. Nel ooncluded that variations in meteorite types are the result of "magmatic differentiation processes similar to those that operated in the Earth's crast". Nel, like the writer and many other geologists, finds it difficult to concelve of the meteorites having formed 139 as individual entities. ge believes, rather, that they must fave resulted from cooling in space within a large planetary body. Bel produced variation diagrams showing differentiation of the Bashveld stratiform sheet from peridotite to anortaosite, and compared this diagram with a variation diagram of meteorites. He concluded that gravitational differentiation separated the original molten material (taie is assaming immiscibility) into silicate and metal phases, bat that separation was not complete. Nel ob- served that the metallic portion of pallasites is "to a certain extent inversely proportional to the amount of iron present in the essentially Mg-silicate", and that pallasites are the most afic in the series of aerolites and are the transitional stage during magmatic differentiation between siderolites and aerolites. In a stady of the Bashveld complex van der Walt (1941) discovered that the formation of chromite and orthopyroxene exerts a reciprocal effect on their respective chemical compositions, which is shown in their rAg ratios (mg MgO mol/agO mol FeO mol). Nel concludes that the same sort of chemical equilibriam an differentiation controlled formation of the pallasites, except that oxygen was very deficient. Geoahemial juilibria: H. brown (1948) has made among the most significant contributions to our knowledge of the 140 origin of meteorites and has made an admirable attempt to place the theory that meteorites originated within an Earthsized planetary body on a thermodynamic basis. brown plotteA variation of percentages of the several major elements in meteorites against the percentage by weight of free metal. On these graphs he thci plotted the variations of the major elements in average igneous terrestrial rocks and plateaa basalts, percentage free metal. These were plotted at zero by extrapolation he showed that terrestrial rooks were natural extensions of the variation curves of meteorites. Alaminam was the only exception founA. Brown also noted that the major element composition of meteorites is strikingly different from the major element composition of terrestrial rooks, and pointedly suggested that ortain low abuadanoe elements are present in the harth's crastal rooks only by"statistioal flactuations". The presenoe of certain ilemeats, e.g. the platinum group, which is strongly siderophile and enormoasly enriched in the metallic phase of meteorites, is due to inoomplete differentiation of Earth's arust. equilibriam conditions it Had cooling been under ideal seems reasonable to believe that certain elements might have been oompletely exoladed from Larth's orust. Brown farther showed that certain achondrit- to meteorites are almost identical to certain terrestrial rocks (e.g., Hess and Henderson showed the bulk composition 141 or the Moore County meteorite to be almost identical with norite), and conclades that it is most difficult to explain their origin other than by differentiation processes within a planet-sized body. Brown and Patterson (1948) made the fundamental assumption that the observed distributions of the elements between the various phases in meteorites represent equilibrium conditions. They assume that equilibrium must have been es- tabliened at temperatures of approximately 300000 and presearee of 105 - 106 atmospheres. These investigators noted the surprieingly smooth de- pendence of the distribution coefficients between the metal and silicate phases upon the affinities of the various elements for oxygen. They found the distribation coefficient dependent on As , the heat of formation, and suggested that the elements distribated themselves between the various phases (metal, silicate, sulfide) under near equilibrium conditions. An example of this, whioh has already been ade. quately disassed in the chapter on mineralogy, is the strong dependence of the distribution ooefticient of Ni on the free metal phase content of a meteorite. Brown and Patterson particularly investigated this observation, for i is the only element for which adequate experimental evidence exists. Zur Strassen had previously measured the equilibrium 142 Ni + f8Si03 U13±03 + Fe at 18400K and one atmosphere N and tound the equilibrium constant to be 7.25 x 103. The equilibrium constant is defined as Iel a xii .s a [jzilm(Felei 0- 3 18400y7. BO% Atm. where "m" and "ai" refer reupectively to the iietal aad sili- cate phases. Lar Strassen found GM± = 7.25 % 10-3, which is approximately 40 times smaller than the value 0.24 observed in gross meteoritic material. Thas there is an enormous dis- orepanoy btween the experimentally determined value of The question of OGb and the OGi observed in meteorites. how this major difference, at the temperatures e:xpected in the interiors of planets, could be explained arose. Brown and Patterson assamd that the temperature at the center of Earth was nearer to 400000 than 3000 0 C. This assumption was based on a lower limit of temperature at which Ug-rich silicates could remain molten and an apper limit net by astronomioal and geophysioal theories (s.g., that of ter Harr). by toe Chatelier's principle, either a pressare or temperature increase would increase the value of Ci (i.e., suitt the reaction to the right). On the assumption that temperatures within an Earth-sised body would be of the same order of magnitade (air. 2000 0 K) as ased by sur I. - - ~.J. 143 Strassen in his determination of ai. Brown and Patterson concluded that the discrepancy could only be explained by an enormous increase in pressure, of the order 105 atmospheres. This pressure is of the same order of magnitude that astron.omers believe to exist within a planet approximately the size of Mars. Brown and Patterson found an even greater discrepancy in the case of %jifor the reaction Mi + FeS S * Fe or, CNi i[ia2 s (i] m(Fe] a phase. , where "a" denotes the sulfide 0ji for this reaction determined in the laboratory at 12000K and one atmosphere equals approximately 1. For gross meteoritic material the value is approximately 0.02. In this reaction, increase of temperature shifts the reaction to the left (doreases O31), while pressare increase shifts it to the right) The temperature at whieh meteoritic silicates are molten exlAes the possibility of a lower temperature. BrowA and Patterson concluded that the discrepancy mast be due to increased pressure -- again of the order of 105 to 16 atmospheres. Such pressures would be quite impossible within a body of the size of meteorites that strike the Earth, or even in bodies hundreds or even thoasands of times more massive. The conclusion is almost inescapable tht ateorites originated within a planet oomFor a vigorous adverse criticism of the work of brown and Patterson read I. m. Klotz, Science, 109, Z48-2bl, 1949. a I - 144 parable in size to Earth. a further conlasion, equally inescapable, is that this planet was in some way shattered, for meteorites reach Earth as small fragments.* "a tatten fiures These figures, which are oba tained by etching the polished surfaces of meteoritic Ni-Fe have long intrigued metallurgists and investigators interested in the origin of meteorites. Until very recently, metallargists were unable to produce these igros. Widmanstatten figures are due to ex- solution phenomena, wherein the two alloys kamaoite and taenit. crystallize in lamellae along octahedral crystal faces. N. A. Owens (1938) ooncladed that saitable heat treatment would lead to the prodation of a two phase structure in certain alloys. Owens discarded the theory that the figures formed by heating in Earth's atmosphere, for the interior of meteorites are not heated in this manner. Furthermore, rapid heating Is known to destroy the figures. Owens, as well as S. -g.J. Smith and J. Young (1939), attributed the figures and the kamaoite-taenite lamellae to the T- O(lattice mechanical transformation. They concluded that meteorites (metal phase of stony meteorites possesses Widmanstatten figures) formed during slow cooling inside some massive heavenly body -- in which the lattice transformation took place so slowly that almost perfect equilibrium prevailed. Smith and Young produced a similar lattice transform- 145 ation in a 10% Ni-F. alloy by slow ooling. Owens and Williams likewise studied the cooling of a Ni-Fe alloy and produced the lattice transformation, and concluded that the structure may form in the range 3500-58000 and requires several months to break down when the temperature drops below 35000. Breakdown will occur only when the temperature drops approximately one degree per day, and not for more rapid rates. Their experiments produced only submicroscopic orystals. Subsequent investigators concluded that only extreme- ly slow cooling could produac the gross Widmanstatten figares observed in meteorites. R. . Mehl and G. S. Barrett (1931) pointed out the fall significance of Widanstatten figures, and these structares are now universally recognised by metallurgists and crystallographers as solid-metal reaotions which operate by crystallographic mechanisms. Mehl and G. Derge (1937) found that "these mechanisas may be described and specified by relations which exist between the parent matrix-lattice and the product or preipitate lattice", the mechanism is two- fold; transformation of the face-eentered cubic lattice of r -iron to the body-oentered cubic lattice of X -iron. Mehl and Derge have sceeded by prolonged slow cooling of Ni-Fe alloy in produoing Widmanast'tten figures of macroscopic size. Also, J. D. Buddhas (1949) suooeeded in pro- 146 dacing significantly large figures by slow oooling of a 27% Mi-Ye alloy, The conolasion is strongly supported that Widanstatten figures could develop only within a large body -- probably of planetary size -- for a smaller body of the present size of meteorites known to us would cool with great rapidity in specs. !t.esa The Barth is generally conceded of Meteorites; by geologists to be at least B x 109 years old. Investiga- tors have long sought to establish the ages of meteorites. If a similar age could be round for meteorites and Earth, this would strongly eaggest that both originated at the same time and may have had similar modes of origin. F. A. Paneth has determined the "ages" of many iron meteorites and at least one stony meteorite (1928). C. A. Baaer (1949) gives a complete bibliography of Paneth's works. Paneth derives ages ranging from 30 million to 8.6 billion years for meteorites. There is no olastering of ages and the meteorites appear to be entirely randomly distributed as to date of origin. This spread of ages is most disconcert- ing to a theory proposing a common origin for meteorites. However, Baaer has proposed a logical explanation for the ages determined by Paneth. Baaer observed from Paneth's measurement of He in meteorites that the content of He was direotly related to the masses of the meteorites measured (1949). The meteorites of small mass contained the most He, while 147 those of large mass contained the least, with a consequent great age for small meteorites and a small age for large meteorites. Bauer proposed the explanation that He was produced in meteorites by cosaio ray bombardment oausing nuclear disraptions. The cosmic rays could not penetrate deeply into ssnes. large Consequently, large masses contained the least He. Bauer concluded that all the He present in meteorites could have been produced in 60 million years, and set this as the apper limit for the time of disruption of the parent planet. In fairness, it should be stated that Bauer's work is statistical and theoretical and is not yet completely proved by experimental evidence. Nonetheless, it is the only ex- planation which has been advanced to explain the great divereity in ages shown in meteorites by He measurements. All other evidence points to the belief that meteorites had a contemporaneous origin. Recently, S. K. Gerling and . G. Pavlova (1951) have determined the ages of two ckondritic meteorites by the argon/potassium ratio (s0 disintegrates by (3-doay to A4 0 ), They found for the Zhotnevy Khator meteorite an age of 3.03 x 10 years, and for the Saratov meteorite the age 3.00 x 10 years. These two ages are in close agreement a a-- a 148 with the earrently accepted valmes for the age of Earth, and saest a common date of origin. Glastie struotares of meteorites: Meteorites ezhibit in most cases strikingly elastic struotares, each as fraotares, faults, sliokensides and brecoia. These features have all been di seassed in the aapter on mineralogy. is sufficient to point oat here that it It seems quite impos- sible that these elastie struatures could have developed in small bodies. They are featares that geologists common- ly associate with massive movements within the Earth. Con- sequently, the olastic structares of meteorites most probably developed wi thin a assive body -- a body possessing a strong gravitational field; in short, a planetary body, oomparable to Earth in size. CO CLUSIONS The remarkable constancy of the traes elements K, Rb, Ba, Sr, Sc, and Zr in chondritic meteorites as evineed by their spectra strongly saggests that thee elements are present in nearly constant quantity in the chondritic meteorites, and rarely vary by a factor greater than 2. The results of those analyses indicate that the followi4 AW abandanco values should be aeaepted. 0.080 0.0008% 0.0008% 0.000% 0.000% 000$P x Rb Ba Sr So Zr A review of the literature indicates that the abundance values for namorous traos elements rests on very scant anain many oases almost entirely on the ana- lytical evidence lysis of a composite sample. Obviously, current trace ele- ment abundanoes in meteorites may be in rather large error. A study of the ratio %K/Rb in meteorites and common ig- neous roots proved that the ratio is nearly oonstant, approximately 100:1. This project was suggested by Dr. L. H. Ahrens, Analysis of the Skaergaard rooks for Sr indioates that this element was present in a sImal amount in the original Skaergaard magma. Wager and Mitohell had previously found Sr abnormally high -- comparable to percentage of K present. The 160 writer oonoludes that this result was due to analytical error. Zirconium, So, and Rb were determined for the first time in the Skaergaard suite of rooks. Both Rb and Zr show char- aeteristio enrichment from base to top of the intrasive, while So content decreases. The behavior of these three elements is farther evidence that the Skaergaard intrusive uandorweat fractional crystallisation in cooling. A review of the astronomical and geological literature led to the conolasion that there is a wetlth of evidence sapporting the shattered planet hypothesis for the origin of meteorites. Negative evidence, and inconsistencies, are few. SUGGESTED RESEARCH In view of the fact that the abndanoe valaes for several trace elements in meteorites were fouA in error daring this investigation, it is sagested that all the other trace elements not analysed for in this thesis be determined by new improved methods. For example, os could not be detected in this investigation, but may be present. It may possibly be detected and determined by saitable chemical concentration. It is suggested that internal standards for silicate meteorite analysis be investigated and applied in fature analyses, The need for large numbers of analyses of meteorites is obvious, if the cosmic abundanoes of the elements from meteorites is to be put on as son a statistical basis as are averages of terrestrial rooks. A possibility exists that the age of meteorites (at least 7 method an apper limit) might be determined by the Sr8 7 -- 3bR Even an upper limit value would by careful analytical work. be extremely interesting. The only previous determinations of ages of silicate meteorites have been by the helium method and a recent determination by the 404:A 40 method. The helium metnod is not considered valid when applied to meteorites, in the opinion of the writer. Age measurements by an indepen- dent method would be very aeful. 152 It is suggested that an extensive researeh be made on tracs element abundanoes in altramafic rooks -- similar to the program on granites, diabases, and basalts in programs now in progress in the .I.T. geology department. BIOGRAPHICAL DATA The writer was born in Atlanta, Georgia, on September 6, 1919. He completed one year's work at the Georgia Insti- tate of Teohnology, 1937-38. After five and a half years military servics he entered Emory University, Atlanta, in 1946. He graduated as Bachelor of Arts in the Sohool of Arts and SOienOes in 1948, and received the degree of Master of Science from Emory University in 1949: master's thesis on "The Geology of Polk County, Georgia". Farther post-graduate work was started at the Massachasetta Institute of Technology in 1949. The writer married Mary Latta in 1942, and has two children, Mary and Naomi. His professional experience includes two years as laboratory instructor at imory University and one summer's field work with the Geological Survey of Georgia. He was for one year editor of the monthly pablication, Atlanta Astronomers' Report. He is at present employed as Research Fellow, Department of Geophysics, and as Instractor, Department of Astronomy, Harvard University. BIBLIOGRAPHY ia, AddisonL. R. (1950) Speotrooheaioal Aa a. Massachuse Wesley Press, Cambridgo, 1. Ahrena, 2. Ahrene, L. H. (1951) New ionic radii values, In press, Geochemioa et Coemoohemioa Ato. 3. Ahrens, L. R., and Gorfinkle, Lorraine G. (1950) Age of extremely ancient pegmatites from soatheastern Manitoba, Nature, 166, p. 149. 4. Allen, Wright, and Clement (1906) Am. J. Sc. (4) U, 385. 5. Allen, dright, and Clement (1912) Am. J. Sao (4) 33, 213. 6. Anilsaa, G., and Dewar, J. (1886) 2roc. Roy. ast. 11, 541-552. 7. Bannister, F. A. 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