American Mineralogist, Volume 67, pages 1012-1020,I9E2
Hyalotekite, a complex lead borosilicate:its crystal
structure and the lone-pair effect of Pb(II)
Peul BntnN Moonn. TexeHenu Anert
Department of the Geophysical Sciences
The University of Chicago
Chicago, Illinois 60637
eNn SusRAre Gsosp
Department of Geological Sciences
U niversity of Washington
Seattle, Washineton 98 195
Abstract
2, a = ll.310(2),b : 10.955(2),
Hyalotekite,ca.Pb2Ba2Ca2[B2(Sir
172Be172)Si6O2a]F,Z:
:90.43(2)",
=
=
y
spacegroup1I from L6ngban,
90.16(2)o,
c 10.317(3)
4,,
B:90.02(2)',
Swedenwas determinedby Pattersonand Fourier techniques,and refinedto R = 0.060for
3713independentreflections.The calculateddensityof3.829 g cm-3 basedon the detailed
chemicalanalysisby Lindstrcim,is in good agreementwith the observedspecificgravity of
3.82.
Twenty-sixindependentatomsoccur in the asymmetricunit. Two sets:Pb(l), Ba(l); and
Pb(2),Ba(2) are associatedspatiallyin pairs. Pb2* and Ba2* are separatedby ca. 0.5A, a
possible segregationfrom the parentl2lm structure due to the 6s2lone-pair effect on Pb2*.
The structure has three principal linked components:g[Si4ot2] four-memberedrings,
clusters.The tetrahedralink to
four-memberedrings and [CazPbaOzoF]
9[Bz(SirnBern)0lz]
form an incompleteframework of composition1[ToOrl] @T6 : BeBaSilein the unit cell)
which remotely resemblesthat of the feldspars.
Mean polyhedral distancesare tslPb(l)-o = 2.80a, Ieleu(t)-o : 2.929, t8lpu(z)-o :
2.804,tetBai2)-o : 2.g37,t8lca-o -- 2.437,t4lsi(t) (: Si:raBer^)-o : 1.597,t'lsl(z)-o :
l . 6 l t , l 4 1 s ( 3 ) - o 1 . 6 1 3t,o l s i ( + F o= l . 6 l 0 , l o l s ( s ) - o = 1 . 6 1 3a n d t a l B - o= l . a 9 6 A . T h eF anion at the origin bonds to four (Pb,Ba)2+and two Ca2*.
The hyalotekite structure has a remote structural kinship with that of gillespite,
BaFeSiaOl6.
Introduction
and F- suggested an unusual crystal-chemical
Hyalotekiteis a rare mineral species,first named problem. The senior author was attracted to the
by Nordenskiold(1877).It was subsequentlystud- speciesbecause of its relatively high content of
ied in more chemical detail by Lindstrrim (1887), Pb2*, and the lone-pair effect expected for this
but since then neither structure type, space group cation in an oxide environment. In addition, its
nor cell parametershave been repofted. Nordens- curious property of easily melting to a glass attractkiold named it from the Greek hyalos and tektos ed our attention.
The refined crystal structure demonstrated that
owing to its property of forming a clear, colorless
glassupon heating.
no simple end-memberformula could be written for
We expresseda special interest in hyalotekite for the compound and what we suggest for such a
severalreasons.First, the relatively large blocky formula is a mere approximation. Furthermore,
massesfrom the only reported locality, Lflngban- Lindstrdm's analysisis demonstratedto be a rather
shyttan, Sweden, much resemble feldspars. Sec- good chemical description of the species,and it
ond, an analysiswhich expressedthe presenceof appears that all subsequent chemical approximamajorpbz*, B*+ ,caz+, Kl+, Be2+,B3*, si4*, 02- tions in the literature were erroneousin someways.
tolz
0003-004)v82l09
l 0-l 0l 2$02.00
MOORE ET AL.: HYALOTEKITE, LONE-PAIR EFFECT
Table l. Hyalotekite:chemicalanalysis
'I
Ba0
0.17
0.B9
0.75
0.09
7. 8 2
0.29
0. 0 9
20.08
Pb0
aJ.tl
Bz0s
3.73
0.lB
0. 0 6
39.47
0.99
0 .0 6
0. 5 9
Na20
Kz0
Be0
Mgo
Ca0
Mn0
Cu0
A lz 0 r
Fea0:
Si 0 z
F
ct
Ign
Total
I 0 0 .3 7
0 .B t
7. 3 0
29.04
4.53
37.13
't.24
10 0. 0 0
0.082
0 .2 8 0
0. 4 4 5
0.033
2 .068
0.061
0.016
1.942
'I
.669
I.s98
0.052
0.012
9.746
0.773
0. 0 2 5
46.802
l L i n d s t r d m( 1 8 8 7 )a n a l y s i s .
2Cowrputed
for PbzBazCaz
Si e0ze] F.
Ig z (s i rr.ge!.)
The computedensity for this'comiposition
i s 3 . 9 9q c m - 3 .
3 A t o m sb a s e do n x 0 = 2 8 a n d a n a l v s i s o f
c o l u m nl . T h e c o m p u t e d e n s i t y f o r t h i s
t o t a l i s 3 , 8 2 9q c m - 3 .
Hyalotekiteis a new structuretype, a borosilicatefluoride of lead, barium and calcium, remotely
related to the feldspar group of minerals, and to the
barium iron silicate,gillespite.
Experimental
Severalspecimenslabelled hyalotekite were examinedand one samplefrom the SmithsonianInstitution (NMNH No. 114716)was selectedfor the
detailed structure study. We thank Mr. Paul E.
Desautelsfor a portion of this sample. Mr. Pete
Dunn, also from the U.S. National Museum, has
analyzeda portion of the samehyalotekiteusing an
electronmicroprobe.He has informed us that hyalotekite fluorescesa light brownish-orangein short
wave ultraviolet radiation and the averagevalue for
the specific gravity is 3.82 determined on four
grains. Since Dunn's observations are in good
agreementwith the more completeanalysisof Lindstrom (1887),we do not list his partial results. The
calculated density for the "ideal formula" and cell
volume of our crystal is 3.99 g cm-3 based on
l0l3
2{PbyBa2Ca2[B2(Si
I I72Be
172)Si6O4]F].However, if
we calculate density on the basis of Lindstrrim's
total analysis,the value is 3.829g cffi 3, in remarkably good accord with the chemical results. Computing the formula unit on the basisof this analysis,
and groupingcations accordingto decreasingionic
radius,we get
(Ke.26sBa1
ea2Pb1
66eCaz
oosNao.oatr,:6
041
(Mnzo+oerMgo.o::CuStroFeStrrAlo.o'
Sie.1e1
B1.5e6)!:
1.e63
(Si1555Bee.a+s)>:z.oooSisOza.ooo(Fo
:o.sog
zzsClo.ozs)>
The minor amountsof Mn2+, Cu2* and Fe3* possibly representimpurities since thesecationsare too
largefor the sitesinto which they were apportioned.
Clearly, our aforementioned "ideal formula" is
only an approximateinterpretationof the complex
chemicalnature of this species.Lindstrom's (1887)
analysis,a calculatedoxide weight percentagefor
the "ideal formula" and atoms in the formula unit
appearin Table 1.
A single crystal fragment was ground into a
sphereof diameter0.12mm, which was usedfor the
X-ray intensity data collection on the computerassistedSyntex P1 diffractometer. The unit cell
dimensionsand the orientation matrix were determined from 15 reflectionswith 20 between20" and
35'. The intensities were measured by the &-20
method utilizing graphite-monochromatized
MoKa
radiationand a scintillationcounter. Variable scans
wereused,the minimumscanratebeing2'min-r at
50 kV and 20 mA. All reflectionswithin a2?limit of
60owere measuredwithin a hemisphereassuming
the spacegroup to be Pl . Intensity distributionson
the diffractometerand on severalprecessionphotographs suggesta triclinic (pseudomonoclinic)cell.
The measuredintensities were corrected for Lorentz, polarization and absorption factors. The intensitiesof reflections(ft + k + I) t' 2n were all
found to be within 3o(1),where o(1) is the standard
deviation of the measuredintensity as determined
by counting statistics. Hence, these reflections
were eliminated from the data set and the space
group was assumedto be 11, which was subsequently confirmed by the structure determination.
The refined cell parametersare a : ll.3l}(DA, a :
90.43(2)" b : 10.955(2)4, B : 90.02(2)o,c :
y : 90.16(2)o,
10.317(3)4,
spacegroup 1T, Z : 2.
Although classical Patterson methods gave the
broad structural features and the gross structural
architecturewas deciphered,the large, heavy cat-
l0l4
MOORE ET AL.: HYALOTEKITE, LONE.PAIR EFFECT
Table 2. Hyalotekite: atomic coordinate parameterst
F i n a l I T c o o r d i n a t e s( R = 0 . 0 6 0 )
Mxy
I 2 l m r e f i n e m e n t( R = 0 . 2 3 )
x
z
y
z
atom;equiooint
P b ( r ) 0 . 2 e 0 ( 7 ' )0 . 1 5 4 3 ( 2 ) 0 . r 7 2 6 ( 2 ) o . o o 4 3 ( 2 )
Ba(l) 0.710
0 . 1 8 7 8 ( 4 )0 . 1 e 2 4 ( 3 )0 . 0 1 0 e ( 2 )
0 .I 7 3
0.183 0.008 Pb
p b ( 2 ) 0 . 2 e 1 ( 7 ) 0 . 8 4 6 0 ( 3 ) 0 .t 7 t e ( 2 ) o . 0 0 4 6 ( 2 )
Ba(2) 0.70e
0 . 8 0 9 7 ( 3 ) 0 . 1 e 2(72 ) o . o r 0 5 ( 2 )
0.827
0.lB3
0.008
Pb; i, y, z
0
0.002
0.229
Ca
0 . 0 0 3(1l )
Ca
1.000
0 . 9 9 9 6l )(
si(l)
Be
0.8r(r)
0 .1 9
0 . 3 1 7 2 ( 2 )0 . 4 e e 5 ( 2 )o . o o o r ( 2 )
0.317
s i( 2 )
s i( 3 )
s i( 4 )
si(5)
1
'|. 0 0
.00
1
'I . 0 0
.00
0 . f e 3 6 ( 2 ) 0 . 5 2 6 7 ( 2 ) 0.2482(2
0 . 8 0 6(r2 ) 0 . 5 2 7 4 ( 2 ) o.24Bo(2
0 . e s e 4 ( 2 ) 0 . 3 ? 2 2 ( 2 ) 0.2626(2
0 . 0 0 0 2 ( 2 ) 0 . 7 2 2 4 ( 1 ) 0.2825(2
0.I94
0.806
0
0
I .00
0.4eee(7)0.3367(6) 0.0305(7)
L
0 . 8 8 4 s ()4 0 . 6 3 8(54 ) o . 3 0 6 8 ( 4 )
0 . 8 8 3 3 ( 5 ) 0 . 4 0 4(34 ) 0 . 2 3
r4 (5 )
0 . 1r 5 e (5 ) 0 . 4 0 3 r ( 5 ) o.232s(
s)
0 . r ' r s 8 ( 40) . 6 3 6 5 ( 4 ) 0 . 3 0 642)(
0.2328(4) 0 . 5 6 8 5 ( 4 o .r o 3 5 ( 4 )
0 . 7 6 6 6 ( 4 ) 0 . 5 7 0 0 ( 4 0 .r 0 3(r4 )
o . 6 0 7 8 ( 4 ) 0 . 4 0 5 4 ( 4 0 . 0 7 9( 4
r)
0.3e3s(4) 0.4044(4 o.o7e6(4)
o .5 0 2 0s() 0.2126(4 0 . 0 8 6 85( )
0 . 4 e e 4 ( 4 ) 0 . 6 6 6 0 ( 4 o .r ' r 3 3 ( 4 )
0 . o o o 7 ( 4 ) 0 . 7 8 3 64 ( 0 . i 4 2 8 ( 4 )
0 . ee88(
4) 0.2082(4 0 . r 6 5 7 ( 4 )
0 . 3 0 2 0 ( 4 ) 0 .5 0 7(54
o .3 4 2 44()
0 . 6 s 7 3 ( 4 ) 0 . 5 0 8 3 ( 4 0.3422(4)
0.884
0.882
0.I f8
0 .I t 6
0.?32
0.768
0.609
0.39t
\
t
0
0
0.301
0.699
0 ( l)
0 ( 2)
0 (3 )
0(4)
0(5)
0(6)
0(7)
0(8)
1. 0 0
r.00
'|
'I.00
.00
1
'| . 0 0
.00
I .00
I .00
o(e) 1.00
o (r o ) 1 . 0 0
o(il ) I . 0 0
0 ( r 2 ) r .00
o ( r 3 ) I'|. 0 0
o ( r 4 ) .00
r
I ,00
0.0000
0 .0000
0.228e(1)
\
0.527
0.527
0.324
0.724
o
si(r)
0.248 si(2)
0 . 2 4 8 5 r ( z r ;x , y , z
0.263 si(4)
0.283 5r(5'
0 . 3 3 7 0 . 0 31
0.640
0.400
0.400
0.640
0.568
0.568
0.403
0.403
0.216
0.664
0.781
0.210
0.509
0.509
0.308
0.228
0,228
0.308
0.102
0.102
0.079
0.079
0.084
0.110
0.143
0.167
0.342
0.342
0 (t )
0(2)
o ( 2 ) ;i ,
0(l); i,
0 (5 )
o ( 5 ) ;i ,
0 (7 )
o ( 7 ) ;i ,
0 ( e)
0(10)
o(il )
o (1 2 )
y, z
y, z
v, z
y, z
o(r3)
0 ( 1 3 ) ;i , y , z
0.0000
'Estimated
s t a n d a r de r r o r s r e f e r t o t h e t a s t d i g i t .
ions such as Pb2+ and Ba2+ presentedproblems.
Fourier synthesesindicateda broad football-shaped
maximum at what was initially believed to be a
singlesite. In the early stages,it was assumedthat
Pb2* and Ba2* formed a solid solution. Difference
Fourier syntheseseventuallyresolvedthis problem,
revealing that the site was split into two partly
occupied sites coupled to each other in a reciprocal
fashion and separatedfrom each other by -0.5A.
At this stage, the structural features were clear and
the framework appeared to be monoclinic with
space group lLlm. Refinement in this space group
convergedto R : 0.23 for 2025 reflections. Admittedly, significant differences existed for many
"equivalent" reflections in l2lm, but these were
neverthelessaveragedto obtain the data set for the
monoclinic refinement.
The structure was then refined in spacegroup 11,
M i s f o r t h e p o p u i a t i o np a r a m e t e r s .
doublingthe list of non-equivalentreflections.With
split heavy atom positions, R : 0.062 for the
converged refinement. During that refinement, it
was clear that one silicon position was partly occupied by a lighter element, probably Be2*, and the
83+ positionalso appearedon anotherposition on a
Fourier map. At this stage, it was noted that all
atom positions could be arranged in pairs, and that
eachpair was related by the inversion center. Due
to such parametercorrelations,it is surprisingthat
the structure refined at all in 11.Refining the averagedpositions,now in spacegroup 11, led to R :
0.060for 3713independentreflections,where
>ilF"t - lFcll
R>tFol
Refinementminimized w(Fo - F")2. The variables
refined included the scale factor, the isotropic sec-
MOORE ET AL.: HYALOTEKITE, LONE-PAIR EFFECT
Table 3. Hyalotekite: anisotropic thermal vibration parameterst
Atom
Urr
lJzz
Uos
2 6 7 ( 3 s l 2 6 5 ( 3)1 1 5 2 ( 2 7 )
Urg
26(25)
22(24\
Uzs
3(23\
tcefficients
i n _ t h e e x p r e s s i o ne x p - [ u r r h 2 + u z z k 2+ u . r t r i i i l l
2 U t z h t + 2 9 r r 7 . 9 1 . E s t i m a t e ds t a n d a r de r r o r s r e f e r t o i h e l a s t d i g . i t .
The coefficients are eachxl0r.
ondaryextinctionfactor (1.5(2)x l0-7), 75 atomic
coordinateparameters,3 site occupancy parameters and 216 anisotropicthermal vibration parameters, givinga total of 296parameters,or an independent data to variable parameter ratio of 12.5:1.
Scatteringcurves for pb2*, Ba2+, Ca2+, Be2*, Si4*
and O-r were obtained from International Tables
(1974)and anomalousdispersioncorrectionsfor all
heaviermetalsfrom Cromer and Liberman fi970).
Table2lists the refinedatomic coordinateparameters, Table 3 the anisotropic thermal vibration
parameters,Table 4 the ellipsoidsof vibration and
their equivalentisotropic temperaturefactors (note
the non-positivedefinite value for Pb(l)), Table 5
the bond distances and angles and Table 6 the
observedand calculatedstructurefactors.r
Descriptionof the structure
The atomic arrangementof hyalotekite is rather
complex. The structural descriptionis divided into
threeparts: (1) the network topology, (2) the ordering ofcations over the tetrahedralpositionsand (3)
the structural distortion due to the lone-pair effect
of Pbz*, which has 6s2in its valenceeleciron shell.
The chemicalanalysisof hyalotekiteby Lindstrrim
(1887)is in very good agreementwith the refined
'To obtain a copy of Table 6, order Document AM-82-20g
from
the BusinessOffice, MineralogicalSociety of America, 2000
Florida, N.W., Washington,D.C. 20009.pleaseremit $1.00in
advancefor the microfiche.
l0t5
structure,which will be subsequentlydiscussedin
more detail.
(l) The network topology. The parent structure of
hyalotekite belongs to space group lllm and possesses17 atoms in the asymmetric unit. As discussedbefore,the real spacegroup for our crystal is
11, a derivative of the parent structure. For purposesof comparison,the previouslyrefinedcoordinates of the monoclinic holosymmetric group are
includedin Table 2.The /T structurehas 26 atoms
in its asymmetricunit. Proceedingfrom l2lm to IT,
the two (Pb,Ba) split into 4 non-equivalent atoms
andSi(2),O(1),O(2),O(5),O(7)and O(13)eachsplit
into 2 non-equivalent atoms, yielding 9 additional
independentpositions.The Pb and Ba appearto be
segregatedin a coupl_edrelationship, this separation
beingonly about0.5A. This is believedto be a lonepair effect, which is discussed later. Deviations
from l2lm symmetry are small, as can be seen in
Table 2.
The structure of hyalotekite is based on an incompleteframework of corner-linked oxygen tetrahedra. Here, we symbolizedthe tetrahedralcation
by T. The underlying structural principle is shown
as a polyhedraldiagramdown [001] in Figure l. A
dominant feature is the occurrence of g[Si4or2]
four-memberedrings, which are nearly in the {001}
plane,approximatelypositionedat z - /+,3/+.Such
a ring involves the Si(2)-, Si(3)-, Si(4)- and Si(5)oxygen tetrahedra.The structure is somewhatreminiscent of the feldspars with a connection of fourand eight-membered rings. However, there are
some major differences.In hyalotekite, the eightmemberedring is not planar but puckered, which
can be written as -Si(5)-O(4)-Si(2FO(5)-Si(t)o ( 7 ) - B - O ( 10 ) - S i ( 5 ) - O ( 4 ) - Si ( 2 ) - O ( 5 ) _ S i (I ) _
O(7)-B-O(10F. The network topology for a feldspar type four-memberedring is uudd, where z and
d symbolize the disposition of the out-of-plane
vertices,being either up (: a) or down (: d). The
scapolitestructure, which also contains 4- and 8memberedrings, is basedon uuuu (dddd) and udud
rings. Hyalotekite differs in two respectswith regard to thesestructures.First, the topology is uddd
fuuuA. Second,the in-planevertices which bridge
to adjacentrings in feldspar and scapolite,are not
linked to other tetrahedral units. Thus, O(ll),
O(12),O(13)and O(14)are not bridgingoxygensand
thesedefine the incompletednature of the tetrahedral framework.
Another four-membered tetrahedral ring occurs
MOORE ET AL.: HYALOTEKITE, LONE-PAIR EFFECT
l0l6
Table 4. Hyalotekite:parametersfor the ellipsoidsof vibrationt
B e q( 4 ' ? )
Atom
0 . 6 7( 3)
0(3)
8(r)
e0(4)
82(r)
2.22(4)
0(4)
80(3)
r6e(3)
86(2)
0.88(3)
0(5)
r5(2)
roo(2)
7e(r)
2.01(3)
0(6)
0 . 6 82( )
o(7)
0 . r 1 2r (0 ) ' r8042(r(33)7 ) 8' rr3( r( e2 )8 ) I l ( ' 1 7 )
e 8 (2 0)
0 .r 3 4 ( 9 )
1 6 7( 3 7 ) r o o ( 3 7 ) 8 3 ( ' , r 4 )
0 .r 4 59( )
0(8)
0 . 0 9 5 ( H ) e2(ro) 84(',I0) 6 ( r 2 )
3 7( ? 9 ) 9 6 ( 1 2 )
0 . r 3 4 ( e ) 1 2 1( 2 q l
0 .r 4 8 ( e ) r 4 3 ( 3)r 126(28) 8 8 (8 )
0(e)
0 . 1 1 9 ( ' 1 0 )B e ( 4 )
0 . 1 2 8 ( 1 0 )e 3 ( 4 )
1 7 7( 3 )
0 . 2 3(48)
oic
i
Pb(l)
..........non-positive definite
B a ( )l
l
2
3
e4(4)
o.r07(2) s2(2)
0 .r 2 4 ( 2 ) r 2 0 ( r 4 ) 2 s ( 4 6 )
6r(r)
0 . 2 3 e ( 3 ) 3 r( r)
Pb(2) r
2
3
'l
ea(2)
2
3
0 . 0 2 8r(5 ) 1 3 3 ( 2 ) 4 4 ( 2 \
0 . r 0 r( 2 ) 1 0 0 ( 2 ) ' r8354((32))
0 . r 5 0 ( 2 ) r3 s ( 2 )
Cal
o .o 8 o (4)
' r7 2 ( 8 )
0 . 0 9 8 ( 3 ) 0 6( 9 0 )
0 . 0 9 9 ( 3 ) tJf,t /J./
r 5 8 (7 )
7 7( 8 \
tuotzf,
rcc(YU./
0 . 0 e 4 ( 6 ) 52(28)
( 6)
o .1 0 2
4 0 ( 2 )7
0 . 1 2 7( 4 ) 1 0 07( )
8 4 r( 0 )
3 e ( 2 5 ) o .e 3 ( 6 )
'r08(8)
12s(?7\
16r(7) 74(6')
?
3
si(l)
s i( 2 )
s i( 3 )
I
2
V
0.r06(2)
0.132(2)
0 . 2 19 (3)
oiq
eib
Atom
76(r)
66(',r
)
r5r(r)
86(21
27(1)
63(r)
102(35) 6e(eo)
0 . 0 e (1s )
r 7 ( e o ) r' r06801
((4r 4) ) e o ( 6 )
e 8 (r o )
0 . 1 0 4 ( 4 ) r 0 7 (14 )
e 8 r( 0 )
8 (r 0 )
0.r2r(3) e3(6)
0 .B e 3( )
)rt),
"1, O
"Le
3 46
()
' r84e0( (6' )r 0 )2 .3 4 (ro )
1
' r1 0 ( 8 ) 5 0 ( 1 0 )
r6(5)
'r
I
2
q
f
5
)
.63(9)
3
e5
()
8 4 (r2 )
0 . o e er '(r) ' l
9 2 ( ' , r ' r )r 6 6 ( e )
0 3( r o )
0 .I 3 7 e( )
0.182(8) r38(6) t2e(5) 78(8)
'r
0 .r 0 7r(0 ) 6 4 (r 4 ) r 4 3 ( 1 2 ) 6 4 ( 2 0 ) .30(8)
0 . r 2 7 ( 9 ) 6 2 ( 2 0 ) 102(21]. 14e(21)
0 . r 4 8 ( 8 ) 4 0 ( ' 1 8 ) 5 5 ( r 1 ) 7 4 (r e )
'l
0 . r 1 7 ( 1 0 ) 5 r ( ' 1 2 ) 46(24) ' l75?o( 2 8 ) . 4 4 ( 8 )
( 2 3)
(2?)
60(27
9
7
0 .r 3 0 e( )
)
'r40(il)
5 e ( r 2 ) 6 7 (r 5 )
0 .r 5 6 ( 8 )
e7(52l,
172(5el
86(4)
7( 4 8 )
97 ( q2\
8 8 (3 )
0 (t 0 )
0 . 0 8 3r 2( ) ' re 4 ( e )
0 .r 3 2 ( 9 ) ' r3 8 ( e o)
3 2( 9 0 )
0 .r 3 6e( )
'r0(r3)
8 r ( r 0 ) o . 8 e 3( )
0. 0 e(24 )
8e(ro)
o .l 0 7 ( 4 ) '1r 33 re((rr77 )) 8 2 ( 1 2 ) r 3 8 ( r 7 )
o .r 7 ( 4 )
e5(7)
4e(17\
'r00(e) 'r4(e) 80(14)
o.o8e(4) 'roe(16)
0.8r(3)
'r
60('r6
0.r0r(4)
83(',rs
)
)
( 6)
0 .r 2 ( 4 ) r 5 8 ( r 5 ) 1 0 2 ( 8 ) 7 3 1
'il
0 . 0 9 9 ( r 5 )e2(26) r (eo) 20(87) r . r o ( r ' l )
0 . r 0 6 ( r 6 )7 7( r 7 ) r 5 6 ( 8 2 ) r o e ( e 0 )
0 . r 4 4 ( r 4 )I 3 (2 0 ) 79(17) 84(',rs)
0 ( r)
2l(re)
0 . r ' r 2 ( r 0 ) 8 r ( i l ) \10(22ll
'159
(24)
108(22)
0 . r 3 0 ( e ) 9 9 (l 8 )
o .r 5 2 ( 9 ) 1 6 7 ( r 4 ) 8 3 ( r 7 ) 78(12)
'r.74(9)
64(12,
0(1)
0 . r 0 8 ( 1 r )5 e ( 7 ) 43(7)
0.144(e) 6s(ro) 74(il) r53(r2)
0.183(8) 38(7) 128(7) 83(e)
0(2)
74(6)
0 . 1 2 4 ( ' 1 r02) 4 ( 8 ) 3 8 ( 6 )
0 .r7 5 ( e ) r 3 7 ( 1 0 ) r 0 7 ( r o ) r 2 8 ( i )l
0 . 2 0 8 ( 8 )| r 3 (r 0 ) 122(6)
42(il )
2.36(10)
]
?6IA\
'r
.28(8)
2 . 2 5r(0 )
1.12(7\
8 ( e ) 'r8 3 ( e )
8 7 ( r 7 ) 32( 90)
4 3 e( o )
e8(r o)
86(6) o . 8 e ( 3 )
r 3 3 ( r 2 ) ' r42(121
3r(
r3) 98(',r3)
1 3 7( 1 2 )
o .r ' r e ( 3 ) e 3 ( i l ) e e ( r o ) e ( r 2 )
0(r2)
Beq(A'z)
0 . r ' r 7 ( ' 1 0 )5 7 ( 8 )
0 . r 7 4 ( e ) 5 7 (e )
0.2r3(8) 5l(7)
o . o e( 4
r)
o .l 0 7 ( 4 )
s i( 4 )
vi
I
?9fA\
'l
0 . 1 0 3r 0( ) 95(27) 6 r( 6 s ) 2 e ( 6 8 ) . 0 5 ( 7 )
0 . r 0 e ( r 0 )t 0 9 ( 1 9 ) J 5 ( 5 b , | r r s ( 7 0 )
o .r 3 2 ( 9 ) r 6 0 ( 2 0 ) 1 0 8 ( r 7 ) 6 C ( r C , l
7 7( e ' )
75(25)
20(23)
'r.24(8)
8 s r( 2 )
16s(25)
0(r3)
0 . 0 9 4t 2( ) r 6 8 (r e )
0 . r 3 r ( 8 ) 8 8 (r 3 )
78(8)
0 .r 4 68( )
0(r4)
62(25)
0 .r r 0 (l 0 ) r 3 e (r 8 ) r t 7 ( 1 2 )
0 . r 2 7 ( s ) 114(22)
' 1 2 r ( r r )r 3012( (210e) ) 152(?6)
8 e (r 5 )
0.15r(8)
'r0r(r2)
8 e (r 2 )
0.r22(r'l)
0 . r s 7l (o ) r 3 2 ( 3 4 ) 4 2 ( 3 4 )
0 .r 7 0 r( 0 ) 4 4 ( 3 3 ) 4 r ( 3 5 )
7\( 2q\
1
iFla\
' | r( r 2 ) r . 8 0 r(o )
e 8 (1 4 )
83(il)
ti
= ; - t h p r i n c i p a l a x i s , p , . = r m s a m p i i t u d e , o i a , a i b , 0 7 " = a n g l e s ( d e - o . ) b e t w e e nt h e i t h p r i n c i p a l a x i s a n d t h e c e l l a x e s 4 , b a n d
E s t i . m a t e ds t a n d a r d e r r o r s i n P a r e n t h e s e s r e f e r t o
c. The equivajent isotrbbic thermal vibration*parifretei-, Beq,-is also listed.
the last digit.
in the structure, approximately situated at z - 0, Vz.
This ring, however, does not share the u,d-type
configuration since two opposing tetrahedra in the
ring are oriented with the z-axis nearly coinciding
with a pseudo-{4} axis through a pair of tetrahedral edges. This tetrahedron is approximately
in composition. The remaining non[Siy+Bey+]Oa
equivalenttetrahedronis a [BOal tetrahedron.For
this ring, all oxygen vertices are linked to other
tetrahedrain the structure.The formal composition
The entire
of this ring would be g[B2(Si3/4Berz)Orz].
tetrahedral incomplete framework would have the
composition 1[ToOro], where 4T6 : BeB+Sirq,
which is the tetrahedral cation content of the unit
cell. The two non-equivalenttetrahedralfour-memberedringslink throughO(5),0(6), O(9),and O(10).
Perhapsthe most striking feature of hyalotekite is
its structural relationship with gillespite, BaFe
[Si4org].The gillespitestructure consistsof sheets
comprisedof 4- and 8-memberedrings; the fourmemberedrings encloseFe2+ and the 8-membered
rings houseBa2*, which is in distorted cubic coordinationand thus belongsto a coordinationpolyhedron of order eight (Pabst, 1943).No cationsoccur
within the hyalotekite 4-membered rings. In addition, the 9[SioOtr]ring is uuud, while in gillespiteit
is uuuu. The corrugatedsheetsparallel to the {001}
plane are metrically similar. In hyalotekite a - b -
MOORE ET AL.: HYALOTEKITE, LONE-PAIR EFFECT
l0l7
Table 5. Hyalotekite:cation-anionbond distancest
Pb(l)
Pb(2)
r u 1 t 1 - s 1 1 1 1 (, ' )? 7 E f E \
Pb(2)-0(ll)(') 2.3s6(5)
- o (l 2 )
2.424(5)
-o(r3)('z) 2.4s3(5)
- 0 (1 2 )
lr\
-0(t4)\-/
2.457(51
2 . s o(ls )
-F
2 E\712\
-o(ta1(')
-o(ts1(3)
-o(6)(')
2 EOr/5\
-F
? tqq/El
- o ( 5 () ' )
/ r \
_0(l;r'r
3.333(6)
-0(3)
3 . 4 7 06()
2.804
Average
Ba(t)
2.57e(5)
2.s8s(3)
3 . 2 0 (1s)
/t '.t \
-0(41
( 6)
3.325
3.465(6)
2.804
-0(2)
Average
B a ( ' l ) - 0 ( 1 4 ) ( ' ? )2 . 6 5 7 ( s )
- o ( t t 1 ( I ) ? . 6 74 ( 6 )
-o(ts1(')
- o (r 2 )
- 0 1 0 (1t )
-F
- 0 (t 1t ' r
-0(8)
_0(3)
Average
(3)
3.441
-Ba('l)
0.439(3)
l . 4 8 3( 8 )
r.484(8)
Average
I .496
r . s 0(7e )
r.50e(8)
0.476(21
t"l
-Si(31t'i
-F
-o(13)(3)
-0(10)t"/
(')
-o(41
- 0 ( 7 1t ' r
-0(r)
Average
-B(')
2.344(4)
2.e04(5)
2.e71(41
3 .r 2 5 ( 6 )
3 . 3 3 46()
3.34s(6)
2.929
-0(8)
!.cyt(f,,
- o t e 1 ( ' ) 'r.604(s)
-0(5)
Average
si(4)-0(12)
/ r \
2 . 3 4 65( )
-0(9)\-,
2.361(I)
2.366(s)
2.476(4)
2 .5 1 4s()
2.s33(s)
-0(3)
-0(?l
Average
3.52s(21
-si1z1(z) 3.4s2(z)
-0(e)
3.580(7)
s i( 2 )
s i 1 t 1 - s 1 7 1 ( '')r . s 6 8 ( s )
'|
.623(
5)
1.597
s i ( 2 )- 0 (r 3 )
-0(3)
-0(5)
-0(4)
Average
si(4)
ca-o(12)
-0(14)(",
2.675(5)
2 . 6 7 (7s )
B a ( 2 ) - o ( 1 3 ) ( ' z2
) .5s8(s)
-0(12)
2.674(5)
-o(rr)(') 2.676(6)
-o(ln;(:) 2'684(5)
-o(5)(r'
2.s23(s)
-F
3.03e(4)
-01+;('z) 3'o8e(5)
-0(2)
3.334(6)
-0(7)
3.360(6)
Average
2.937
3.457(3)
- B a( 2)
si(l) (= sir^Betr)
B-0(e)
- 0 (l 0 ) ( r )
-0(7)
-0(8)
Ba(2)
s i( 3 )
'l
1.581(5)
r.610(s)
'1.626(5)
r.62e(s)
si(3)-0(r4)
-0(1)
-o(2)
-0(6)
'I
.6ll
Average
I .6'13
.582(5)
'r.6ro(s)
1.624(5)
r.634(s)
s i( 5 )
I
qa?/i'l
r.602(s)
'r
.609(5
)
1.636(s)
'I
.610
si(5)-0(lr)
- 0 (l )
-o(ro)(')
-o(4)
1.5e4(s)
1.60e(s)
1.621(5)
r.630(5)
Averaqe
1.613
2.s57(s)
2.437
3 .0 2 8( 7)
rEstlmated
s t a n d a r de r r o r s i n p a r e n t h e s e rse f e r t o t h e . ' l a s t d i 9 i t .
The equivalent positions (referred to Table Z) are
d e s i g n a t e da s s u p e r s c r i p t sa n d a r e ( 1 ) = - x , - y , - z ; ( 2 ) =
r 2 + y , , . " + z (; 3 1 =
1+x,
11.134,while in gillespite,itis a\D, - 10.60A.It is
temptingto speculatethat a gillespite-relatedphase,
suchas PbFeSiaOlsor gillespiteitself, may exist at
Lingban, coexistingwith hyalotekite.
The remainingatoms are (Pb,Ba),Ca and F. The
Ca atoms are situated along the 002 line above and
below F at the inversion center which joins to 2Ca,
and 4(Pb,Ba)atoms.The (Pb,Ba)atoms are located
within the large distorted eight-membered rings
much like the alkaline earth atoms in feldspar.
r-x, Z-y,4-2.
appears to possess a fully ordered occupancy of
[SiO4] tetrahedra by Sia+ exclusively. The large
differences in radii and/or atomic numbers among
t41Be2*(0.27A)and t4tB3*(0.tzA); and t+J5ir+
(0.264) make refinement of site populations for
these atoms possible. Throughout this study, we
used the values of Shannon and Prewitt (1969)for
effective ionic radii. For an effective radius e1tz19z: 1.35A, the interatomic distanceaverageswould
betarBe-O: 1.624, t+19-6 : l.47Aand t4lsi-O -1.61A.Interatomicdistanceslisted in Table 5 are in
(2) The ordering of cations over tetrahedral posi- good accord with these values. The averages
tions. The four-ring involving S(2)-S(5) at z - V4 t4tsi(zFo : 1.61, t4ts(3Fo : 1.61, ta15i14pg=
t0lE
MOORE ET AL.: HYALOTEKITE, LONE-PAIR EFFECT
0il2).17
b
0(
r pt(t)oo
r Bo(l).0t
0(r3).34
0(r0).rl
0 (14).34
r 8o(2).01
pirzr.ooo(2)
Fig. 1. Polyhedralrepresentationof hyalotekitedown [001].The sectionO 4 z4 t/zis shown.The [SiaOru]ring is not shaded;the
T(l) (: Siy+Be17a)Oa
tetrahedraare ruled and the BOa tetrahedraare stippled.Heightsare given as fractionalcoordinatesin l. The
asymmetricunit in Table 2 is labelled.Terminal oxygensare underlined.
1.61and t4tSi(S)-O: 1.614 are in excellentagreement with the anticipated average.The value t4lB-O
= 1.50,{ is only slightly larger than the expected
value.The valuet4tsi(t)-O : 1.60A,where Si(l) Be17a
is only slightly smallerthan the expected
Si37a
averagefor thesetwo cations.This raisesthe question of whether or not 83* insteadof Be2+ substitutes at this site, since thesecationsare practically
impossibleto distinguishby their X-ray scattering
powers alone. However, a contradiction arises in
formal charge assignmentfor the formula unit and,
in the absenceoffurther evidence for deciding the
site population of Si(l), we prefer to write it as
It should be further noted that LindSi37aBe17a.
strom's (1887)analysisalso shows the presenceof
this amount of BeO in the compound.The formula
for the tetrahedral fraction can therefore be written
[Sir(SirnBerD)BzOzs]with two such units in the unit
cell.
The ellipsoidsof vibration listed in Table 4 sug-
MOORE ET AL,: HYALOTEKITE, LONE-PAIR EFFECT
gest that the assignmentsof scattering curves and
the site population refinements in Table 2 are a
fairly good approximation to the atoms present. If
A13* or Sia* were substitutedfor B3*, we would
expect a substantial decrease in the equivalent
isotropic^thermalparameter. On the other hand, B"o
: 1.10A2for B suggeststhat this site correspondsto
boron, or possiblyeven someminor site vacancies.
It is possible,however, that substitution of minor
Si4* for 83* would induce local disorder causinga
subsequentincreasein B"o.
(3) The structural distortion due to Pbz+. Hyalotekite is an examplewhere Pb2* with its 6s2lonepair
evincesa particularly noticeable effect on the entire
structure. Hyalotekite's aristotype belongs to a
space group with considerably higher symmetry
than found in the actual structure: that is l2lm + IT .
Order-disorder in the tetrahedral framework does
not appearto be a causefor this, since Si(l) and B
have site symmetriesC2 and C", respectively,and
do not split into non-equivalentSi (or B) positions
in the triclinic subgroup,unlike feldspar in which
Al-Si ordering destroys such symmetry elements.
In hyalotekite, these special positions merely becomegeneralpositions,and the generalpositionsin
the aristotype split into two sets of general positions. In these general positions, there does not
appearto be any evidenceof ordering.
lf we extract the large cations and their coordinating anions, the picture changesdrastically. Figure 2 shows the Pb(1)zPb(2)zO2oF
cluster, which is
composedof four fused PbOTFpolyhedra (polyhedron No. 197,of Britton and Dunitz, 1973).They
are roughly equivalent, and would be identical in 12l
m. Each polyhedron shares two faces with two
other polyhedra and the common F vertex is also
corner-linked to the fourth polyhedron. Thus, F
links to four Pb2*(Ba2*) cations, and also to two
Ca2+cationsabove and below. The CaOTFpolyhedron corresponds to polyhedron No. l2l of maximal symmetry C" in Britton and Dunitz and shares
triangular faces with the PbOzF polyhedra. polyhedron No. 197 can be regarded as having a square
pyramidal cap with F at the vertex. In this structure, four triangular faces are shared, two with
adjacent Pb2+ cations and two with adjacent Ca2*
cations.
The remarkablefeature about the PbOTFgroup is
that all bonds to the face-sharing vertices are the
shortestfor their polyhedra (Fig. 2 and Table 5),
while the remaining three Pb-O bonds on the oppo-
l0l9
356
0 (tt(2)-.tg
Fig. 2. Spoke diagram of the PbaO26Fcluster in hyalotekite.
The additional Ca above and below F at the origin are omitted
(the CarPboO26Fcluster). Heights are shown as fractional
coordinatesin z and bond distancesare shown.
site side of the F atom are the longest for their
polyhedra. This is interpreted as the result of the
lone pair-bond effect with the 6s2lone pair located
oppositethe tightly bound F- anion. This model is
reminiscentof the argumentsapplied to sulfosaltsin
general and galena in particular (Moore, manuscript), where the lone pair-bond pair interactions
lead to bond length dilation. In fact, on the bond
pair side, the Pb-O distancesrange from 2.36 to
2.594. The shortest is not much larger than the
effectivetolp6++-g : 2.184 separation.
Pb2* and Baz* are split in hyalotekite, separated
by about 0.4-0.54. From the site populationrefinement (Table2), atotal of 1.162Pb2+cationsoccurs
per 28 oxygens.However, Lindstrcim'sanalysisin
Table I indicatesan aliquot of 1.669Pb2+ atoms.
This differenceis not easily explicable, since the
solid solution structural effect of a cation with a
lone pair (such as Pb2*) and a cation with inert gas
configuration(such as Ba2*) is not clear. It is also
possiblethat some analytical error may exist in the
quantitative separation of Pb and Ba. Due to the
lone pair effect, the t8lPb2*-O distancesrange from
2.36 to 3.474. The tElCa-Odistancesrange from
2.34 to 2.564 and telBa-O from 2.66 to 3.36A.
Clearly, the most severepolyhedral distortion occurs for Pb2+. Did Pb2+ and Ba2* occur in solid
solution at the clystallizing temperature of hyalotekite and then partition as the phase cooled? This is
an intriguing question, since an affirmative answer
would suggest that the high temperature space
1020
MOORE ET AL.: HYALOTEKITE, LONE-PAIR EFFECT
group would be l2lm and that the lone pair effect
would be temperature-dependent,
at least for Pb2*
oxysalts. A possibility that this effect may indeed
exist appearsin Hurlbut (1955)where conclusive
evidenceshowedthat somewulfenites,Pb2+MoOa,
are in fact polar, and that centrosymmetric wulfenites may themselves be merohedrally twinned on
{001}.High temperaturecrystallographicstudiesof
polar wulfenites and hyalotekite would be instructive.
EAR76-13373(Geochemistry) for support in this study, and P.
Boving and C. Wan for assistancein data collection. We join in
thanking the U.S. National Museum (Smithsonian Institution)
for donation of the samplefor study.
References
Acknowledgments
Britton, D. and Dunitz, J. D. (1973)A complete catalogueof
polyhedra with eight or fewer vertices. Acta Crystallographica. A29.362-371.
Cromer,D. T. and Liberman, D. (1970)Relativisticcalculation
of anomalousscatteringfactors for X-rays. Los Alamos Scientific Laboratory, University of California Report LA-4403,
Universityof California-34.
Hurlbut, C. S., Jr. (1955) Wulfenite symmetry as shown on
crystalsfrom Jugoslavia.American Mineralogist, 40, 857-E60.
International Tables for X-ray Crystallography, Vol. 4. Revised
and SupplementaryTables(1974).Ibers, J. A. and Hamilton,
W. C. Eds., Kynoch Press,Birmingham.
Lindstrrim, G. (lEE7) Om hyalotekit fr6n L6ngban. Ofversigt af
Kongliga Svenska Vetenskaps-Akademiens Fdrhandlingar,
44,589-593.
Nordenskidld,A. E. (1E77)Nya mineralierfrtn LAngban.Geologiska FdreningensFtirhandlingar, 3, 376-384.
Pabst, A. (1943) Crystal structure of gillespite, BaFeSiaOls.
American Mineralogist, 28, 372-190.
Shannon,R. D. and Prewitt, C. T. (1969)Efective ionic radii in
oxides and fluorides. Acta Crystallographica, 825, 925-946.
P.B.M. and T.A. acknowledgethe grant NSF EAR79-1E259
(Geochemistry) and the Materials Research Laboratory grant
(NSF) to The University of Chicago, and S.G. thanks NSF
Manuscriptreceived,February lI, 1982;
acceptedfor publication, May l l, 1982.
Pb2+ lone pair effects
Table 5 includesonly the cation-aniondistances
in absenceof a good qualitative model for the lone
pair effect on nearestbond pairs. If any prediction
were to be made regarding the locus of the lone
pair, it would be toward O(1), O(3), 0(6) for Pb(l)
and O(2), O(4) and O(5) for Pb(2) by mere inspection of the Pb2+-Obond distances.Theseare those
verticeswhich opposethe coordinatedF- anion, or
better yet, the capped squarepyramid.