UNIVERSITY OF SOUTH ALABAMA
GY 302: Crystallography &
Mineralogy
Lecture 21: Inosilicates 1
Pyroxenes and Pyroxenoids
Last Time
Class VIII Minerals
Sorosilicates
Cyclosilicates (3, 4 and 6 fold coordination)
1.
2.
Sorosilicates
Mineral
Zoisite
Clinozoisite
Epidote
Allanite
Lawsonite
Pumpellyite
Vesuvianite (Idocrase)
Hemimorphite
Formula
Ca2Al3O(SiO4)(Si2O7)(OH)
Ca2Al3O(SiO4)(Si2O7)(OH)
Ca2(Al,Fe)Al2O(SiO4)(Si2O7)(OH)
(Ca,Ce) 2(Fe,Fe)Al2O(SiO4)(Si2O7)(OH)
CaAl2SiO7(OH)2·H2O
Ca2MgAl2(SiO4)(Si2O7)(OH)2·H2O
Ca10Mg2Al4(SiO4)5(Si2O7)2(OH)4
Zn4Si2O7(OH)2·(H2O)
System
Orthorhombic
Monoclinic
Monoclinic
Monoclinic
Orthorhombic
Monoclinic
Tetragonal
Orthorhombic
Sorosilicate Minerals
Hemimorphite
[Zn4Si2O7(OH)2·H2O]
Crystal: Orthorhombic
Pt. Group: 2mm
Habit: massive to mammillary
SG: 3.45; H: 5
L: vitreous; Str: white
Col: colorless, brown, to grey
Clev: perfect [001]
Optics: Biaxial (+); bir=0.020
nα=1.61; nβ=1.62, nγ=1.736
http://webmineral.com/data/Hemimorphite.shtml
Named after the hemimorphic nature of the crystals.
Cyclosilicates
Mineral
Beryl
“Tourmaline”
Cordierite
Axinite
Dioptase
Formula
Be3Al2Si6O18
(Na,Ca)(Li,Mg,Al)(Al,Fe,Mn) 6(BO3)3(Si6O18)(OH)4
Al3(Mg, Fe)2(AlSi5O18)
(Ca, Mn, Fe)3Al2(BO3)Si4O12(OH)
CuSiO2(OH)2
Silicate rings come in 3, 4 and 6 fold
structures. 8-fold structures also
occur in nature (e.g., sulfur)
System
Hexagonal
Hexagonal (Trigonal)
Orthorhombic
Triclinic
Hexagonal (Trigonal)
Cyclosilicate Minerals
6 fold ring structure
Cyclosilicate Minerals (6-fold rings)
Beryl
Crystal: Hexagonal
Pt. Group: 6/m 2/m 2/m
Habit: euhedral, columnar
SG: 2.76; H: 7.5-8
L: vitreous; Str: white
Col: blue, yellow, red, green
Clev: imperfect
Optics: Uniaxial (-); bir=0.004-0.007
ne=1.564; nw=1.568
http://webmineral.com/specimens/picshow.php?id=123
[Be3Al2Si6O18 ]
From the ancient Greek, beryllos, signifying a "precious blue-green color of sea water" stone.
Today’s Agenda
Class VIII Minerals: Inosilicates (part 1)
1.
General Introduction to Inosilicates
2.
Pyroxenes
3.
Pyroxenoids
Inosilicates
The “chain” silicates come in 2 main “flavors”
Single chains (Si:O = 1:3)
(Pyroxene Group)
(Pyroxenoid Group)
Double chains (Si:O = 1:2.5)
(Amphibole Group)
Inosilicates (single chain)
Two major sub groups of pyroxenes
are distinguished on the basis of
crystal structure:
1) Orthopyroxenes (orthorhombic)
2) Clinopyroxenes (monoclinic)
http://www.uwgb.edu/dutchs/GRAPHIC0/ROCKMIN/ATOM-STRUCT/PyroxChain.gif
Inosilicates (single chain: pyroxenes)
General formula: XYSiO3 or XY(Si,Al)2O6
X[larger ions] = Ca2+, Na+, Fe2+ and/or Mg2+; rarely Zn2+, Mn2+, Li+
Y[smaller ions] = Cr3+, Al3+, Fe3+, Mn3+
Si:O ratio is 1:3
(octahedrally coordinated
cations between SiO3 chains)
http://www.tulane.edu/~sanelson/images/opx-cpxphasediag.gif
Inosilicates (single chain: pyroxenes)
General formula: XYSiO3 or XY(Si,Al)2O6
X[larger ions] = Ca2+, Na+, Fe2+ and/or Mg2+; rarely Zn2+, Mn2+, Li+
Y[smaller ions] = Cr3+, Al3+, Fe3+, Mn3+
Monoclinic
Orthorhombic
Si:O ratio is 1:3
(octahedrally coordinated
cations between SiO3 chains
produce orthorhombic or
monoclinic symmetries)
http://ruby.colorado.edu
Inosilicates (single chain; pyroxenoids)
General formula: X2SiO3
X[larger ions] = Ca2+, Na+, Fe2+ and/or Mg2+
http://ruby.colorado.edu
Si:O ratio is 1:3
(larger cations force triclinic
symmetry)
Inosilicates (single chain)
Orthopyroxene: orthorhombic minerals
(5)
Hypersthene, Enstatite, Ferrosilite, Donpeacorite,
Nchwaningite
Clinopyroxene: monoclinic minerals
(18)
Clinoenstitite, clinoferrosilite, pigeonite, diopside,
hedenbergite, spudomene
Pyroxenoid: Triclinic minerals (lots)
wollanstonite, pectolite, rhodonite
Inosilicates (single chain)
Inosilicate Minerals (orthopyroxene)
Enstitite [Mg2Si2O6]
Crystal: Orthorhombic
Pt. Group: 2/m 2/m 2/m
Habit: laminar, massive, fibrous
SG: 3.2; H: 5.5
L: vitreous to pearly; Str: grey
Col: white, yellow, brown, gray
Clev: [110]; [010] good
Optics: Biaxial (+); bir=0.009
nα=1.65; nβ=1.65, nγ=1.66
Occurrence: mafic intrusive rocks
From the Greek enstates - "opponent."
Inosilicate Minerals (orthopyroxene)
2009 textbook’s “mineral” (p265)
Orthopyroxenes
hyperstene
http://upload.wikimedia.org/wikipedia/en/4/42/Pyrox_names.png
http://ruby.colorado.edu/~smyth/min/images/enstatite.gif
Enstitite is actually one member of a
continuous series suite of
“orthopyroxene” (Enstitite-Ferrosilite).
Inosilicate Minerals (orthopyroxene)
http://www.geo2all.com/vb/
Enstitite (En) can also be related
to many other silicate minerals
through this phase diagram
http://web.pdx.edu/~ruzickaa/meteorites/McSween/Fo-Qz.gif
There is complete Mg-Fe solid solution between the pyroxenes, and as with
most Mg-Fe solid solutions, the Mg-rich end members crystallize at higher
temperatures than the Fe-rich end members.
Inosilicate Minerals (clinopyroxenes)
There are more options for
ternary plots as there is more
variability in cation composition
Clinopyroxenes
… and you are going to ♥ the
phase diagram possibilities
Inosilicate Minerals (clinopyroxene)
Augite
(Ca,Na)(Mg,Fe,Al)(Si,Al)2O6
Crystal: Monoclinic
Pt. Group: 2/m
Habit: columnar, massive, fibrous
SG: 3.4; H: 5 to 6.5
L: vitreous; Str: green-grey
Col: green-grey
Clev: perfect [110], poor [010]
Optics: Biaxial (+); bir = 0.0260
nα=1.68; nβ=1.684, nγ=1.706
Occurrence: basic igneous & metamorphic rocks
http://webmineral.com/data/Augite.shtml
From the Greek auge - "luster."
Inosilicate Minerals (clinopyroxene)
Augite
(Ca,Na)(Mg,Fe,Al)(Si,Al)2O6
Crystal: Monoclinic
Pt. Group: 2/m
Habit: columnar, massive, fibrous
SG: 3.4; H: 5 to 6.5
L: vitreous; Str: green-grey
Col: green-grey
Clev: perfect [110], poor [010]
Optics: Biaxial (+); bir = 0.0260
nα=1.68; nβ=1.684, nγ=1.706
Occurrence: basic igneous & metamorphic rocks
http://www.mii.org/Minerals/photoaugite.html
From the Greek auge - "luster."
Inosilicate Minerals (clinopyroxene)
Spodumene [LiAlSi2O6]
Crystal: Monoclinic
Pt. Group: 2/m
Habit: bladed
SG: 3.15; H: 6.5-7
L: vitreous; Str: white
Col: grey-white, yellow, pink
Clev: [110] perfect; [100] good
Optics: Biaxial (+); bir = 0.014-0.018
nα=1.648; nβ=1.655, nγ=1.662
Occurrence: Li-bearing pegmatites
http://www.dkimages.com/discover/previews/867/70006667.JPG
From from the Greek, spodoumenos, "burnt to ash,"
alluding to its color
Inosilicate Minerals (clinopyroxene)
Pigeonite
[(Mg,Ca,Fe2+)Si2O6]
Crystal: Monoclinic
Pt. Group: 2/m
Habit: prismatic
SG: 3.38; H: 6
L: vitreous, dull; Str: white
Col: green, brown
Clev: [001], good
Optics: Biaxial (+); bir=0.021-0.030
http://webmineral.com/specimens/picshow.php?id=2262
nα=1.683; nβ=1.684, nγ=1.704
Occurrence: shallow intermediate/ mafic intrusive igneous rocks
Pigeonite
http://www.tulane.edu/~sanelson/images/opx-cpxphasediag.gif
Slow cooling allows pigeonite to convert to other orthopyroxenes
Exsolution
Inosilicate Minerals (clinopyroxene)
Jadeite [NaAlSi2O6]
Crystal: Monoclinic
Pt. Group: 2/m
Habit: columnar, fibrous
SG: 3.3; H: 6.5
L: vitreous; Str: white
Col: green, white, blue-grey, pale purple
Clev: good [110]
From Spanish, piedra de ijada, "stone of the
side," because its supposed to cure kidney
Optics: Biaxial (+); bir = 0.006-0.021
ailments if applied to the side of the body.
nα=1.640; nβ=1.645, nγ=1.652
Occurrence: blueschist-type metamorphic rocks
Inosilicate Minerals (clinopyroxene)
Jade…
Comes in 2 varieties
1) Jadeite (a pyroxene)
2) Nephrite jade or “actinolite”;
(an amphibole)
Inosilicate Minerals (pyroxenoids)
Wollastonite [CaSiO3]
Crystal: Triclinic
Pt. Group: 1
Habit: massive, fibrous
SG: 2.84; H: 5
L: silky; Str: white
Col: white, yellow, grey, brown, red
Clev: [100] perfect; [102] [001] good
Optics: Biaxial (-); bir = 0.014-0.016
nα=1.615; nβ=1.627, nγ=1.629
Occurrence: metamorphosed limestone and dolostone
http://www.leescorp.com
Named after English mineralogist W. H. Wollaston (1766-1828).
Inosilicate Minerals (pyroxenoids)
Pectolite
[NaCa2Si3O8(OH)]
Crystal: Triclinic
Pt. Group: 1
Habit: acicular, globular
SG: 2.86; H: 5
L: silky; Str: white
Col: white, grey, light green
Clev: [001], [100] perfect
Optics: Biaxial (+); bir = 0.032
nα=1.594; nβ=1.603, nγ=1.631
http://csm.jmu.edu/minerals/minerals%5C+PectoliteVA.jpg
From the Greek pektos - "compacted"
Occurrence: Secondary vug-filling mineral in basalt
Inosilicate Minerals (pyroxenoids)
Rhodonite
[Mn(Fe2+,Mg,Ca)SiO3]
Crystal: Triclinic
Pt. Group: 1
Habit: granular, tabular, massive
SG: 3.6; H: 6
L: vitreous; Str: white
Col: pink, rose red, yellow
Clev: [110] perfect
http://www.webmineral.com/data/Rhodonite.shtml
Optics: Biaxial (+); bir = 0.0130
From the Greek rhodos - "rose colored."
nα=1.711; nβ=1.714, nγ=1.724
Occurrence: Mn-bearing hydrothermal & metamorphic rocks
Identifying Rock-forming Minerals
What do?
using your hand lens....
1) distinguish how many different
minerals you have in the rock
2) test the best representatives you
can find
• luster, cleavage, colour (easy)
•hardness, streak (doable)
•habit, specific gravity (unlikely)
Today’s Stuff To Do
1.
Poster drafts due Thursday in class
Next Time
1.
Inosilicates part 2: Amphiboles
GY 302: Crystallography and
Mineralogy
Lecture 21: Silicates 4: Pyroxenes and
Pyroxenoids
Instructor: Dr. Doug Haywick
dhaywick@southalabama.edu
This is a free open access lecture, but not for commercial purposes.
For personal use only.