American Mineralogist, Volume60, pages273-279, 1975
Szaibelyite,Mgr(OH)[BrO4(OH)]: CrystalStructure,
Pseudosymmetry,
and Polymorphism
YosHroTerrucuI, nNp Yesugtno Kunon
Mineralogical Institute, Faculty of Science,Uniuersityof Tokyo,
Hongo, Tokyo I13, Japan
Abstract
Basedon x- andy-coordinatesdeterminedby Peng,Wu, and Chang(1963),a completestructurehas
beenestablished
(ascharite)
for szaibelyite
and refinedto R : 5.9percent,usinga crystalfrom KiinigshallHindenburg,Germany,twinnedon (100):P2,/a, a 12.577(2),
b 10.393(2),
c 3.139(l)A, B 95.88(2)",Z =
4[Mgr(OH)B2O1(OH)],
calculateddensity2.738g/cm3.Two non-equivalent
chainsof octahedraformed
by oxygenatoms about magnesiumarejoined by sharingcornersto form sheetsparallelto (100).The
sheetsare held togetherby pyroborategroups,BrO.(OH).Each octahedralchain has a strongtwofold
parallelto the c axis.The pseudosymmetry
screwpseudosymmetry
is suchthat the chainis nearlyperfectly transformedby the screwoperationsinto itselfwith averageatomicdisplacement
of only 0.056(4)A.
This situationtheoreticallypermitsgenerationof polymorphicvariationsof the structure.The celldimens i o n s a n d s p a c e g r o u ptswoof s i m p l e v a r i a t i o n s a r e : (ll2) a. 5 l l , b 1 0 . 3 9 3 , c 1
33
. 9 A ,P 2 r 2 r 2 r ; ( 2 ) a 2 5 . 0 2 2 ,
b 10.393,
c 3.139A, 1 90.00",P2,/a.
Introduction
crystal data for ascharitefrom Stassfurt,Germany:
: 3.14A, b : 10.42A, c : 25.05A, and space
a
Szaibelyite is a basic hydrous borate of
magnesium,
MgHBOr, which was first describedby group 822'2.
In contrastto theseorthorhombiccells,Penget al
Peters(1861).Other mineralshavingthe samecom(1963)
Kitai,
reportedascharitefrom north-eastern
position have also been described;for example,
: 12.50A, b : 10.42A,,c
monoclinic:
China,
to
be
a
ascharite(Feit, l89l) and camsellite(Ellsworthand
:
:95"40', andspacegroupP2rla.Using
Poitevin,l92l). Though Winchell(1929)suggested 3.144,0
from optical study that camselliteand szaibelyite iftO reflectionsand the Pattersonfunction, they carstructureanalysisand
might be different, there has been a generally ried out a two-dimensional
showed
that
the
structure
does
contain pyroborate
acceptedview that thesethree mineralsare identical
becausethey give similar X-ray powder diffraction groupsin the form [B,O4(OH)].Althoughtheir work
elucidatedthe generalstructuralschemeof ascharite,
patterns(Watanabe,1939;Schaller,1942'1.
The mineralogical confusion surrounding this and a brief accountof the structurehas sinceapmineralwasprincipallydueto its fibrouscrystalhabit peared(Kudoh and Tak6uchi,1973),full detailsof
which has hinderedcrystallo-chemical
characteriza- the structure were neededin order to assessthe
tion. Basedon crudefiber-rotationand Weissenberg differentreportedcrystal data and to settlethe conphotographs,the first singlecrystaldata werepro- fusedstatusof natural MgHBO'.
posedby Tak6uchi(1957)for sussexite,
the Mn anaExperimental
log of szaibelyite,
from Mine Hill, SussexCounty,
New Jersey.With this information,the powderdifMaterial from Kdnigshall-Hindenburgin Reyersfractionpatternof camsellite
from BritishColumbia hausenbei Gdttingen was kindly placedat our diswas indexed.An orthorhombiccell was proposed posal by the late Professor O. Braitsch, who
havingthe dimensions:
4 : 10.34A, b : 12.45A, describedthe material as ascharite.HigherJevelWeisc : 3.21A, and probableplanegroup pgg for the senbergphotographsabout the fiber axis invariably
zero-levelwith c as rotation axis. Tak6uchi(1958) exhibited an unusual pattern (Fig. l) that was
further suggestedthe existenceof pyroboratepoly- readily interpretedas due to twinning of monoions in the structureof MgHBO, basedon infrared clinic crystals across(100). Betweenstrong reflecabsorption spectra, and proposed the formula tions in Figure l, diffuse streaks are observed
HrMgrOBrOu.
Braitsch(1960)reportedthe following along the festoons correspondingto lattice rows
273
Y. TAKEUCHI, AND Y. KUDOH
'w
t
.:r;.:-.i.:::.
,:&:
,*
*,
*
..s'
@.
for hkl reflectionswas confirmedin the subsequent
processof structurerefinement.
Intensitiesof reflectionsthus measuredwere then
correctedfor Lorentz and polarization factors and
reducedto structurefactors.No absorptioncorrec: 49.2cm-'). Of the 699reflection wasmade(pc,,i<o
tions, thosewith intensitiessmallerthan 2 o (I) were
excluded,and the remaining466reflectionswereused
for structuredetermination.
StructureDetermination
t+
of atomsgivenby Penget
The x- andy-coordinates
,i
values for structure
i'
(1963)
as
initial
used
were
al
periodicity
of the c axis is
4a7A
the
determination.Since
*
o
of atomswere
z
coordinates
very short, approximate
structure
-%,.,
two-dimensional
the
t&8i
a*.
from
t-.,t*
e
rl*,
readily derived
",
account
of
(1963)
by
taking
given
Peng
et
al
by
photograph(c axis rotation;
Frc. l. SecondlevelWeissenberg
consideraand
pairs
to
twinning,
and
crystallo-chemical
due
ofreflections
atomic distances
CuKa radiation),showing
diffusestreaks.Indicesof some of the reflectionsfrom twin in- tions. A Fourier map was then calculatedusing
dividualsA and B are indicated.
structure-factorsigns basedupon this initial set of
atomic coordinates. In the map, the x- and ythe
existence
parallel to the a* axis, these indicating
coordinatesof atoms reportedby Penget al (1963)
in
the
reflections
were
found to be essentially correct. After zof disorderin the structure.Some
along
the
photograph are also slightly diffuse
coordinatesof atoms were slightly adjustedin the
the
extent,
map, a calculationof structurefactorsyieldedR :
horizontal line, showing that, to some
20.6percent.
crystal bearsa fiber structure.
were
The atomic parameterswere refined by the fullintensities
collected
and
The unit cell data
program,Onrts, written for InN'I
X
0.15
matrix
least-squares
0.
l0
having
dimensions
composite
from a twin
X 0.30 mm along the a*, b, and c axes,respectively. 7090computer by Busing, Martin, and Levy (1962)
For comThe cell dimensions obtained by single-crystal and modifiedby Iitaka for Hlrnc s020n.
putations,an empiricalweightingfactor was used
A) are a :
diffractometry(Cu Ka,, tr = 1.540518
A, r = 3.139(l)A, p :
of the form: w; : t/(a + F + cF'zo)(Cruickshank,
12.577(2)
A, b : 10.393(2)
of MgHBO, occurin this 1965).The valuesq and c which minimized the
95.88(2)".Eight molecules
unit cell, the calculateddensitybeing 2.738g/cry". variation of (F. - F") with Fo were 20 and 2/300
According to the survey made by Schaller(1942), respectively.Cycles of refinementconvergedwhen
observeddensitiesfor natural MgHBOTfrom various the value of R was reducedto 5.9 percentfor the
localitiesvary from 2.60 g/cms to 2.76 g/cm3. The set of 466 reflections.
Sinceit was anticipatedthat the hydrogenatoms
spacegroup is P2rfa, h\l and 0k0 reflectionsbeing
whenft and k are odd. The above might be located, a differenceFourier map was
absentrespectively
crystal data agreewith thosereportedby Penget al preparedat this final stage.The map indeedrevealed
(1963).We failedto find evidence
for the.B-centeredtwo residualpeaks;one is at the positionx:0.21,
orthorhombic crystal reportedby Braitsch(1960). y : 0.39,z : 0.66betweenO(4) (=OH) and O(2),
A total of 699independentreflectionsfrom one in- and the other at the positionx : 0.33,y : 0.28,
dividual of the twin compositewere then measured z : O.l0 between0(6) (:OH) and O(3) (Fig. 2).
on a four-circlediffractometerup to sin d : 0.906. After includinghydrogenatoms at thesepositions,
The hk\ reflectionsare common to the individual the value of R was reducedto 5.7 percent.The
crystals,so, to estimatethe volume ratio, we com- O(4)-H and O(6)-H bond lengthswere found to be
Since,however,the
pared intensitiesof severalpairs of corresponding 0.80 A and 1.02A respectively.
.
.
.
O(3) hydrogenbond is, as will be disreflectionsfrom individual crystals.The ratio was O(6)-H
O(2)
found to be essentiallyunity; the intensitiesof ftkO cussed later, weaker than the O(4)-H
be
should
length
bond
reflections were therefore weighted by 0.5 with hydrogenbond, the O(6)-H
the
above
coordiThus,
length.
respectto thoseof other reflections.This scalefactor smallerthan O(4)-H
/ ov.B
t
t
SZAIBELYITE, STRUCTURE, PSEUDOSYMMETRY,AND POLYMORPHISM
natesfor hydrogenatoms are of uncertainaccuracy.
The atomic coordinatesand thermal parametersare
given in Table l; the observedand calculatedstructure factors are comparedin Table 2.
Descriptionof Structure
TlsI-r l.
of Szaibelyite
Atomic Parameters
parameters
Positional
Atom
Ms(1)
Mc(z)
B(1)
B(2)
Projectedalongthe c axis,the structureis essentially the sameas that reportedby Penget al (1963).The o ( 1 )
maximum differencein the x- and y-coordinatesof o ( 2 )
o ( 3)
atomsis found for the O(3) atom,the differencebeing o ( 4 )
0.09A along the a axis.The structure(Fig. 2) con- oo (( 56 ))
tains distortedMg-O octahedrawhich shareedgesto
form a chain,two octahedrain width, parallelto the c
axis.Two suchnon-equivalent
chains,onea so-called Atom
g(1)
A chainformedby Mg(l)-O octahedraand the other M}dg(z)
B
(
a .Bchain of Mg(2)-O octahedra,sharecorners(Fig. B ( 21 ))
2) to form a sheetparallel to (100).
The sheetsare held togetherby pyroborateions oo (( 21 ))
The pyroborateion (Fig. 3) doesnot o ( 3 )
[BrO4(OH)]3-.
o(4)
have all its oxygenatoms in a plane; instead,the o ( 5 )
directionsof the normalsto the two slantinstriansles o ( 6 )
The
v
e(iz)
"
o 5047(21
o 4129\2)
o 1372(7)
0.3072(7)
0
o
0
o
13?3(2)
4208(21
1680(8)
047218)
0
0
o
o
2348(8)
?104(8)
?598(28)
6253(30)
0 80
1 10
| 42
r.43
o.0762(4)
0 1012(4)
o 247614'
o 24gtl4)
o 4134(41
0 4084(4)
0
0
0
o
0
0
0616(4)
2e08(5)
1548(5)
4485(4)
0434(4)
2953(5)
0
0
0
0
0
0
7804(1?)
7750(17)
7208(18)
60?8(18)
7155(1?)
2059(18)
| 24
1.36
1 68
1 s0
| 21
r-27
Anisotropic
temperature
l3zz
/3 n
ractors
Bss
(X 104)
Fp
Fzz
Ftt
16(1)
21(1)
28(6)
30(6)
13(2)
7e(21
1e(?)
2317)
215(23)
291(24)
3Bs(s4)
3?2(88)
1(2)
2\21
-10(6)
-5(5)
28(5)
2(6)
24(5) - 14(?)
2s(18)
70122)
33(21)
14122)
26(3)
29(4)
31(4)
34(4)
27(3\
27(3')
23(5)
2215)
3o(5)
25(5)
21(5)
20(5)
302(54)
3?9(61)
450(61)
s79(55)
300(54)
354(58)
2(3)
-2(3)
-0(4)
-0(3)
-2(3)
-4(3)
24(rr)
15(14)
26(13)
1(14)
16(i3) -18(15)
1s(13) 43(14)
1 5( 1 2)
1 ( 1 4)
2o\t2)
6(14)
expression
used
for the anisotropic
thermal
parameters
was
* prruz* Prrr2*zfrrr**zP',fr +zfrrlal]
.*o[-tprrr,2
(oneis BOsand the other BOrOH) differ by 32.0(2)".
This featureof the pyroborateion is in linewith those
(Berger,1950)and
of the pyroborateionsin Co2B2Ou
(Tak6uchi,1952).However,comparedto
in Mg2B2Ou
the B-O-B angleof 130.6(7)',which is very closeto
anglein
that of 131.5'in MgrBrOu,thecorresponding
CorBrOuhasa largervalueof 153'.The B-O lengths
and O-B-O angles are given in Tables 3 and 4,
respectively.
with
The hydroxl ion at O(4), which is associated
pyroborate
with
ion, formsa hydrogenbond
O(2)
the
of anotheradjacention, the O(4)-O(2)distancebeing
2.564(7)A. On the other hand,the hydroxylion at
0(6), which is coordinated by three magnesium
atoms,has a closeanion neighbor,O(3), at the distance of 2.812(7)A. tnis distanceand the valence
sumsat 0(6) and O(3) (Table3) suggestthe existence
of a weak hydrogenbond betweenthem.The valence
sums were calculatedusing the techniquesgiven by
Donnay and Allmann (1970).
Pseudosymrnetry
and Polymorphism
Ftc. 2. The structure of szaibelyite projected on (001); thermal
ellipsoids are shown. The B-O bonds are indicated by solid bars;
hydrogen bonds by broken lines (a weak hydrogen bond between
O(6):OH and O(3) is not marked).
In eachoctahedralchain,the octahedraarerelated
to each other by inversion about the centers of
symmetry which belong to the spacegroup P2'/a.
Passingthrough the centersof symmetryand hence
parallelto the chain axis,a strongpseudo2r axisex-
276
Y, TAKEUCHI. AND Y. KUDOH
ists in the chain (Fig. a). The operationsof this
pseudosymmetry
combinedwith the inversiongenerate in the chain pseudo-mirror planes perpendicular to the chain axis and betweenthe inversion
centers.The situationis readilyobservedin Figure5,
which showsa view of the structurealongthe b axis.
Sincethe octahedralchainsarejoined, as mentioned
previously,to form sheetsin the mannershownin
Figure 4, the sheetsthemselvespossessthe same
Tlsrr
k
6
8
l0
t2
ll
0
3
4
I
)!
0
0
63699
63
61
21259
9l
96
7t)
67
3{339
t3
20
{l
34
t6
l?
31
3?
45
45
ll4
|4
8383|
l{
!{
17
11
89
93
22
23
?(i
85
14
43
7t
71,
31
30
l9
14
')o
22
12
t{
l?
l('
3a
3ti
??
80
I 0;
Ioi
lt6
t5l
:6
:l)
t3
!6
?!
?5
80
83
13
12
?0
15
:8
?9
3!
28
2t
)5
tOt
too
rl
13
('8
08
?;
8I
??
3l
?0?oI
l3l
t29
(i3
62
it
!3
81
?9
20
t1
ri
17
20
22
ll
9
I
3
4
5
6
8
I
l0
9
9
l0
I0
lo
l0
l0
ll
tl
1l
ll
ll
t2
12
l:
t2
12
t2
t3
13
l3
t4
lt
l4
l{
-t4
-t{
-14
0
0
l3
-13
-12
-t!
-l!
l1
-lr
-ll
IO
t0
-9
I
-9
9
,8
-8
-8
-8
-8
-8
-7
15
15
lt4
t2t
i1
1ti
27
27
t6567lO
31
30
6?636r
1)
73
5?
61
12
l0
?6
69
{3
44
5256-53
62
6t
-7
2018-5?
65
67
4t
42
l?
13
2525-40
4l
39
0
33
0
38
o?614-4
02020-4
02927-4
0{950-4
0
106
05041-3
0
27
0
l9
o
28
0
t?
o2?26-3
9
{iI
28
(i2
tit
18
62
Observed and Calculated Structure Factors for Szaibelyite
lqF.hk
%F.h
{
2.
i
-7
-?
8
-6
0
-6
6
-5
3
I
6
9
2
,5
4
-5
,5
-5
8
l0
ll
-4
I
6
,6
J6
3?
$F.hk
29
36
-{
.4
96
-4
28
l5
25
l0
-3
-3
-3
-3
33
35
-3
-3
20
l9
13
13
20
l8
8
9
?7
20
20
39
2t
l0
40
55
2l
18
58
2i
50
50
!(i
25
(,
26
t8
23
44
23
12
39
5l
19
t9
53
29
49
52
25
28
19
2E
l4
60
63
16
26
t4
t2
l8
9t
16
25
25
3?
43
58
89
tr2
7
ll
13
{3
3l
63
t7
26
2l
54
r?
3l
4?
30
14
53
58
15
J6
I I
t2
I I
8?
15
24
ta
30
44
54
85
r0?
t3
12
12
38
31
63
17
2A
22
53
t8
31
41
of the twopseudosymmetry.
The pseudosymmetry
fold screwaxis is such that the octahedralsheetis
transformedby its operationsnearly perfectlyinto
itself with the averageatomic displacementof only
0.056(4)A along the c axis; the maximum displacement being 0.244(7)A (faUte S).
The structureof szaibelyitecan be dividedinto two
unit slabs,eachboundedby octahedralsheets(Fig.
5), that are relatedto eachother by inversionabout
l0
rr
0
2
3
3
5
l0
l l
0
2
3
6
7
2
4
6
{t
{I
35 -33
444361
t4
t2
ll
t4
2t
t9
t41269
3?
4l
5?5374
545475
35
3t
433?7a
24237t0
20
l9
34
33
2t2684
61
56
r28
t2)
20228
23229
104
to3
42379
56
55
34
3l
2a
23
93
8?
88
85
?0
?l
39
35
15
ll
2{j
19
34
32
47
44
?l
69
65
55
ll4
108
109
r 13
51
52
19
t9
{3
4r
23
18
40
39
34
3?
80
7l
26
25
27
26
?6
79
28
29
L6
16
34
27
19
16
16
16
?5
73
11
72
83
8l
35
3l
2526-86
6362-88
38
38
13
15
{5
49
14
8
57
55
46
47
26
29
t9
t6
36
38
18
19
2A
27
47
49
44
45
5?
58
47
49
t3
ll
18
t8
16
15
ro5
I l0
19
20
I
5
8
l0
6
6
6
2
5
6
7
Z
7
1
I
I
2
3
I
8
9
I
I
lO
t0
I0
l0
lt
ll
ll
12
tz
12
-14
-13
-12
-r2
-t2
-ll
_il
-ll
-lt
-10
-t0
_10
,9
-9
-9
-9
-9
-9
_9
-6
-8
-8
,?
-?
-?
-7
-7
-6
,6
-6
-6
-6
-6
-5
-5
-5
-5
,5
-5
-4
-4
-4
0
t
5
6
1
8
o
I
rb
Fc
Fo
Fc
t9
54
75
45
16
2t
15
43
25
2l
24
34
30
43
33
It
19
16
12
l9
39
23
56
16
16
2t
13
60
30
{2
24
!i
24
36
27
14
88
2)
16
22
22
13
l3
31
29
2l
l8
!6
39
22
l4
12
16
40
35
38
55
16
57
80
46
l8
22
l?
36
26
24
24
38
30
45
29
!4
20
l3
16
20
40
t7
56
15
20
20
15
60
3l
39
26
!i
24
34
26
t3
82
15
l8
2l
2l
t3
9
33
3r
?l
i6
27
39
20
l?
t3
13
42
39
39
55
t29
42
27
25
50
50
44
47
44
r39
31
4a
19
49
35
16
24
42
26
23
5I
5l
44
46
4l
t42
3l
44
15
45
36
tt
25
68
38
29
23
29
64
19
27
36
18
52
26
22
55
3{
23
26
54
16
24
?l
4l
29
23
29
6?
18
29
36
t5
53
21
24
54
34
25
23
5l
16
24
I
lo
I
3
7
h
s
I I
IO
22
12
37
25
76
18
20
14
189
43
{8
50
27
2l
23
t6
14
18
16
t7
62
12
20
t9
?6
25
22
l8
35
35
57
16
20
22
25
42
22
25
39
43
56
63
25
t8
15
15
{6
ll
22
?9
21
19
31
45
16
31
l?
20
14
4A
20
l3
34
2l
72
16
l?
13
r94
35
45
44
27
19
22
19
II
t?
l{
36
6t
ll
20
l7
26
25
22
l?
36
36
58
18
22
25
2a
45
22
26
43
47
60
65
25
t9
l5
13
48
ll
25
J0
27
21
33
47
15
33
13
22
l5
52
I
I
6
9
9
9
t0
IO
ii
-9
-9
-9
-8
-8
-8
-7
-7
-6
-6
-5
,5
-4
-+
-3
,3
-3
-3
-3
-2
-2
-2
,l
,t
-l
23
20
z8
22
19
l8
l4
t5
t4
22
29
3l
l2
21
l3
2L
49
15
58
28
36
37
t9
15
22
ll
26
3?
12
2l
l2
14
36
13
12
33
15
25
4{
16
8l
lE
t9
46
:l
39
3E
t5
22
19
2E
2r
20
20
15
13
II
ZO
26
30
ll
22
16
20
53
13
5l
3l
36
36
2l
16
24
12
29
34
t3
23
I
15
35
II
t?
34
I{
2|
{3
t{
El
t7
18
II
t6
35
3i
ll
l l
l ?
33
30
t2
39
33
l{
13
I !
26
25
25
t9
16
34
23
15
t{
2A
12
35
{?
16
16
t6
37
27
3t
35
13
15
25
27
27
l9
l0
3{
t5
r{
r!
27
12
35
50
t5
l?
t5
39
2A
29
3{
14
15
SZAIBELYITE, STRUCTURE, PSEUDOSYMMETRY, AND POLYMORPHISM
T,rrsl-s4.
Coordination
277
O-O Distances and Bond Aneles
Distuce
group
o(2)
o(3)
o(3)
o(2)
B ( 1 )- O ( 2 )
B ( 1 )- o ( 3 )
B ( 1 )- O ( 3 )
B(2) triangle
o(3)
o ( + )( s )
o(5)
o ( a )( s)
o(5)
Ftc. 3. The configuration of the pyroborarc ron, [B,OTOHF-,
viewed along the b axis.
the centersof symmetryin the sheets(Fig. 5). It is
then possible,becauseof the pseudosymmetry,to
derivea structurein which eachunit slabis relatedto
its adjacentslabsnot by inversionbut by twofold
screwoperations.Only very slight adjustmentsare
requiredin the z coordinatesof atoms in the octahedralsheetsto achievethis structure.In this case,
the twofold screwoperations,whoseaxesare parallel
to the c axis,may be regardedasstackingoperations.
The operationsof this set of twofold screwaxesand
those of the original twofold screwaxesparallel to
o(2) (c)
o(2) [e](cl
o(5) [c]
o(5) [i]
Mg(2) octahedron
0(6)
o(1)[e]
2. 139
0.310
B(2)
Valence
sum
o(t) (s)
2 006
Estimated erro"s
+ Hydrogen bond.
2 051
0.349
2.118
0.336
1.357
1.034
0.338
o(3)
1 413
0.920
o(4) = oH
o(5)
o(4)
1.351
1.046
2 161
0.300
2 085
0.334
1 396
0 963
t. 883
1 403
0-949
2. 214
0 292
1.337
1.088
2.132
0.330
2.037
116 ?(5)
1 2 1 .7 ( 5 )
1213(5)
O ( 5 )[ c )
o(5)
o(2) [s)[c)
o ( 5 )t i )
o(5)
o(5) (cl
o { 5 )t i i
o{s) ti)
o(5)
o(5)
0 ( 6 )( c )
o ( 1 )( e )
o(4)
O ( 1 )t s )
o ( 1 )t c J
o(4)
o(1) ts)[c]
o(1)ts)
O ( 1 )( s t ( c l
o(1) (sl
O ( 1) ( s ) ( c )
o ( 1 )( s ) [ c ]
o(21
o ( a )( s )
o(3)
0(6)
in O - O distances
r3o 6(?)
r?1 0(2)
o(2)(s)[c] 3 030
2 ss1
o ( 2 )t e )
0(6)
0 ( 6 )( c )
Mc(2)
2.382
2.381
2 389
B ( r ) - o ( 3 )- B ( 2 )
o(2)-o(3)-o(5)
Tlst-e 3. Bond Lengthsand ValenceSumsof Szaibelyite*
Mc(1)
r25 1(1)"
11s.5(6)
1154(8)
B ( 2 )- o ( a )[ s )
B ( 2 )- o ( 5 )
B ( 2 )- o ( 4 )( s )
Mg( 1 ) octahedron
Angle
2 4o3
2.388
2.34r
3 041
3 065
3, 13e
3 o3s
2.914
2.s74
3.089
2 82o
3 139
2 82'.1
139
023
952
774
005
058
779
?85
881
014
139
564
2.8L2
are 1 0.00?.{
(s), [c), (g),
(i) are code indicators showin.g coordinates of atoms
equivalent by space group operation to the atoms at ryz.
Corresponding
operatrons are:
tvofold screw at 114, !, lfz
( s I
truslation
c
Ic]
glide a at x, 114, z
t gl
inversioD center at 1,12, O, l/2.
t i )
Two code indicators
in sequence imply an atom related to the one at
ryz by successive application of the tvo symbolized operations.
the b axis in the unit slab form a group, generatingin
the new structure a third set of screw axes parallel to
the direction correspondingto a* of szaibelyite.The
resulting structure thereforehas spacegroup P2r2r2r.
2 140
0.326
0(6)=OH
2037
0.3?7
2048
0 350
2.035
0.357
Mean
2.088
1 3?3
t 3?9
" Computed with the val.ence sum program provided by Prof. Gabrtelle
Donnay. Bond lengths (A) are given in the first line of each pair, and bond
valence (v. u. ) in the second. Estimated errors in individual bond lengths
are 10. 005 A for ug - O, and t o. oro .& for B - O.
FIc. 4. The single octahedral sheet formed by ,4 and I chains;
projection along the c axis Pseudosymmetryelements of 2, are rndicated.
278
Y. TAKEUCHI. AND Y. KUDOH
o-,
(-}
r-
A_ chain
of atoms
in the Mg(1)
octahedron
z
xy
MC(l)
o(5)
o(5)'
o(2)
0(6)
0.504?
0.41.34
0.5866
0.6012
0.4084
0.13?3
0. 0434
- 0. 0434
0.2092
0.2593
o.2348
0 7155
0.2445
0. 7?50
0. 2059
12,
Coordinates of atoms in Mg(1)r octahedra
*'
y'
zl
Me(l)'
0.4953
0.4953
-0.13?3
-0.13?3
o.7652
0. ?809
o(5)
0.4134
0. 0434
0.?155
o(5)'
0.5866
0.5866
-0.0434
-0.0434
r.2845
1.2866
o(2),
0.3988
0.3988
-o,2092
-o.2092
r.2250
0(6),
0.5916
0.5916
-0.2593
-0. 2593
0,794r
0.?811
Az'lel
0.049
0.007
(2)
0.103
(2,
0.041
B - chain
Coordinates
Mc(2)
o(1)
o(6)
o(4)
o(1)'
Coordinates
of atoms
0. 4L29
0.4238
0.4084
0.2481
0.5762
in the Mg(2)
octahedron
v
z
0. 4208
0 . 5 6i 6
0.2953
0. 4485
0.4384
0. ?104
0.2196
0.2059
0.60?8
0. 7804
ol atoms in Mg(2)'
.0_
o
0
v^,----9--
celt is formed of the
a,o. u. [
*,"lou^,*,nr"o
monoclinicmodificationhavinga periodicityof 25 A from the unit
upperdiagramshowsthe c axisprojection,the
cellsof szaibelyite;
lower diagram b axis projection. Note that this monoclinic
modificationhasan orthogonalcellwith its uniqueaxisparallelto
The twofold screwaxesin szaibelyiterethe c axis of szaibelyite.
main in the twinnedcell only aslocalsymmetry;theyare henceindicatedin the upperdiagramby dottedarrows,and in the lowerby
conventionalnotation but open style.
Tlnrs 5. Pseudosymmetry
of OctahedralChains
Coordinates
0
6
Flc. 5. The D axis projectionof the structureboundedby y :
-Vt and % approximately.Solidcircle:B, shadedcircle:Mg, open
circle:O, double open circle:OH.
t2,
12,
octahedra
x
v
z'
Ms(2)'
0.5871
0.5871
0.5792
0.5792
0.2896
0.2819
o(1)
0, 4238
0.5616
0.2196
o(1)'
0.5?62
0,5762
0.4384
0.4384
0. ?804
o. 7822
0. 005
42,
o(6),
0.5916
0.5916
o. 7047
0,7047
0.7941
0. ?811
0.041
a2\
o(4),
0.7519
0.?519
0.5515
0.5515
o.3922
0.3146
0.244
A"'(Al
o. o24
The coordinates
in the first line of each pair given for the atoms ol Mg(l),
and Mg(2)' octahedra
are for the case in which the atoh is related to the
corresponding
atom in the Mg(1) or Mg(2) octahedron by inversion operation about the point at LI 2, O, | / 2 of the space group P2t /a, while those in
the second line are for the case in which the atom ie theoretically
transforhed
from the corresponding
atom by twofold screw operation
about a
hlrpothetical
axis al 1f2,0, z; the value of z' for the latter
case i6 gived by
l/2 + z + a(x' - x) sin(/-90)/c,
Numbers in brackets shov the multiplicity
of atoms.
this
In termsof lto's (1950)theoryon polymorphism,
orthorhombic structure may conveniently be describedas a polysynthetictwin of szaibelyitetaking
place on the scaleof a half unit cell'
Sinceit is conceivablethat sucha twin may occur
on variousscalesof the unit slab(:6u11unitcell),we
can theoretically derive various polymorphic (or
polytypic) structures.Among possiblepolymorphic
forms, one worth noting is the casein which twinningstake placeon the scaleof two unit slabs,nameIn this parly, on the scaleof a unit cell of szaibelyite.
slabsare
unit
axes
of
screw
ticular case,the twofold
(Fig.
6). They
cell
orthogonal
locatedin the resulting
(or
stacking)
group
twinning
with
the
a
do not form
operations.The twinning operationsof the twofold
screwaxesform a group only with the invenion of
the unit slab,generatinga setof glide planesperpendicular to the c axis. Therefore,this polymorphic
structure, despiteits orthogonal cell, has a monoTesLs 6. BasicPolymorphicForms of Szaibelyite
CelI dimensions
( A)
Space group
abc
577
10
393
139
monoclinic
2
orthorhombi.c
12.511
r0 393
3 139
3
monoclinic
25. O22
10. 393
3 139
Cell dimensions
present material
12
3
I
p = 9 s8 8
p2tla
P212Jr
t r = 9 oo. o
pzr/a
of the forms 2 and 3 were calculated from those of the
given ln the first line of this table
SZAIBELYITE, STRUCTURE, PSEUDOSYMMETRY, AN D POLYMORPHISM
279
clinic space group P2r/a with its new unique axis Moore for providing his unpublisheddata on sussexiteand for
along the c axis of szaibelyite.Though this ortho- commentingon our paper.Computationswerecarriedout at the
Centerof the Universityof Tokyo.
gonalcell hasdimensionssimilarto thosereportedby Computer
Braitsch(1960)for his orthorhombic crystal,it obReferences
viously has differentsymmetry.So far as our study
(1950)The crystalstructureof cobaltpyroborate.
was concerned,it was not possibleto derive the Brncrn, S. V.
Acta Chem.Scand.4, 1054-1065.
.B-centeredorthorhombic modification from the Bnetrscs, O. (1960)Die Borateund Phosphateim Zechsteinsalz
szaibelyitestructure.
Sudhannovers.
Fortschr.Mineral. 38, 190-191.
If the 'twinning'takesplacein a randomfashion, BusrNG,W. R., K. O. Mlnrn, ANDH. A. Lnvv (1962)Or.rls, a
ForrnlN crystallographicleast squaresprogram. u.s. Nat.
the resultingstructurewill evidentlygive a diffraction
Tech.Inform. .Seru.OnNl-ru 305.
pattern in which reflections,other than hk|, are
method.In,
CnurcrsHlNr, D. W. J. (1965)Errorsin least-squares
diffusealongthe directionperpendicularto the slabs.
J. S. Rotlet, Ed., Computing Methods in Crystallography.
The diffusestreakswe observedin the Weissenberg PergamonPress,New York.
photographsof szaibelyite(Fig. l) then indicatethat DoNNAy,Glrntsrlr, nNo R. AlllllNtt (1970)How to recognize
O'z-,OH-, and HrO in crystalstructuresdeterminedby X-rays.
the crystal contains this sort of disorder.The cell
Am. Mineral. 55, 1003-1015.
groups
dimensionsand space
of the abovetwo simple Errswonrn, H. V., nxp E. PorrEvIN(1921)Camsellite,a new
polymorphic structures are compared in Table 6
borate mineral from British Columbia,Canada.Trans.Royal
togetherwith thoseof szaibelyite.
Soc.Can. Sec.IV, Ser. III,15, l-lE.
Accordingto ,P. B. Moore (privatecommunica- Ferr, W. (1891) Ober Ascharit, ein neuesBorsiiure-Mineral.
Chem.-Ztg.15, 327.
tion), the crystals of sussexite,MnHBOr, from
Polymorphisn.Maruzen, Tokyo.
SterlingHill, New Jersey,are isotypicwith szaibely- Iro, T. (1950)X-ray Studieson
Cryst.
KupoH, Y., rNo Y. Tlrfucul (1973)Ascharite,BzHzMEzOs.
ite. Thus this structure is apparently the strucStruct. Comm.2. 595-598.
ture type for the crystalsof the szaibelyite-sussexitePruc, Csrs-Csur.lc,Csrxc-Yrj wu, lxo h-HsIrc CHANc(1963)
series. Ellsworth and Poitevin (1921), however,
Crystal structureof ascharite.Sci. Sinica, 12, 176l-1764(In
Russian).
observed parallel extinction of camsellite from
Studienaus
British Columbia, and they suggestedthat the PErERs,K. F. (1861)Geologischeund mineralogische
ausder Umgegendvon
dem siiddstlichenUngarn,insbesondere
crystalwould be orthorhombic.The powder diffracR6zbdnya.2. Teil. S. -8. Akad. Wiss. lVien,44' 8l-185.
tion lines of camsellitefrom the samelocality can in Scsewen, WALDEMART. (1942\ The identity of ascharite,
camsellite,and p-ascharitewith szaibelyite,and some other
fact be indexed(Takduchi,1957)by an orthorhombic
relationsof the magnesiumborateminerals.Am. Mineral.27,
cell of the secondtype in Table 6. Therefore,crystals
46748t.
of camsellite from this locality may well be
TnrsucHI, Y. (1952) The crystal structure of magnesium
orthorhombic.In conclusion,a reinvestigation
of
pyroborate.Acta. Crystallogr.5, 574-581.
natural crystalsof the szaibelyite-sussexite
seriesis (1957) The interpretationof X-ray powder diffraction
series.Mineral.J.2,78-89.
suggestedbearingthe abovestructuralrelationships patternsof the szaibelyite-sussexite
(1958) Infrared absorption and structuresof borate
in mind, so that the long standingmineralogicalcon- polyatomic ions. Mineral. J. 2,245-268.
fusion of the seriescan be unravelled.
Am. Mineral.
WrNcueu, A. N. (1929)Camselliteand szaibelyite.
Acknowledgments
We wish to acknowledgethe late ProfessorO. Braitsch for
kindly placingspecimensof aschariteat our disposal,Professor
Y. Iitaka for his kind help in intensitymeasurement,
and Dr.
A. Kato for discussion.We are erateful to ProfessorPaul B.
14. 48-49.
Wlreuur, Tlreo (1939) Kotoite, ein neuesgesteinsbildendes
Magnesiumborat.Mineral. Petrogr. Mitt. 50, M8-463.
Manucript receiued,August 23, 1974; accepted
for publication,Nooember7, 1974.