American Mineralogist, Volume 68, pages 996-1003, 1963
Cerite, REe(Fe3+,MgXSiOd6(SiO3OH)(OH)s:
its crystal structure
and relation to whitlockite
Peul BnrnN MoonB
Department of the GeophysicalSciences
The University of Chicago, Chicago, Illinois 60637
eNo JrNcnueN Sner.r
X-ray Laboratory, Graduate School
Wuhan College of Geology, Beijing, China
Abstract
cerite, (Ce,La,Nd,Ca)e(Fe3*,Mg,AlXSiO4)6(SiO3OHXOH)3,
rhombohedral, a
10.779(6),
c : 38.061(7)
A, Z : 6, spacegroup R3c, is nearly isostructuralto whitlockite,
CaqMg(PO+)o(PO3OH).
R : 0.032for 1711independentreflections.
Cerite is related to a large family of "bracelet and pinwheel" structures derived from
glaserite, KNal(SOn)2. Rods of two kinds run parallel to the c-axis. One rod is partly
disordered at (002) and includes the (SiO3OH) tetrahedron and (OH)- etroups,the latter
bonded to the RE ions. The other rod at (x,y,z) which is fully occupied is based on the
corner-, edge-, and face-linkages of Si(l)Oa and Si(2)O+ tetrahedra and RE(I)OgOH,
RE(2)OEOHand RE(3)O6OH polyhedra. Omitting the bond to OH, the anhydrous REO3
group is a polyhedron of order 8 and has maximal point symmetry D2d. The OH- ligands
bond through a rhombus-shaped window in this polyhedron. Average distances are
tetRE(t)-o : 2.59, terRE(2)-o = 2.55, telRE(3)-o : 2.59, t6l(Mg,Fe3+,AlF : 2.07,
tols(tFo : 1.63and t4rsi(2)-o = 1.63A.
It is suggestedthat cerite probably has F- analogues,and is related to a substantial
family of rare earth silicates with rhombohedral structures such as cappelenite,okanoganite and steenstrupine.
Introduction
Experimental procedure
Cerite, a silicate of the rare earths (:RE), was first
named and described by Jcins Jacob Berzelius. The
mineral from the Bastniis Mine, Riddarhyttan, Sweden,
provided Berzelius and his students with a source for
several new rare earth elements, including cerium
(Jorpes, 1966).
Cerite has been suspected to be isostructural with
whitlockite, CagMg(POr)o(PO3OH),just as beckelite,
Ca2RE3(SiOa)3(OH)
is isostructural with apatite, Ca2Ca3
(PO4)3(OH). In addition, tcirnebohmite, RE2AI(OH)
(SiOl)2, which occurs with cerite at the type locality, is
found to be isostructural with fornacite, pbzCu(OH)
(AsOrXCrOr) (Shen and Moore, 1982). Therefore, a
structure study of cerite seemed highly desirable. In
addition, a suspectedkinship with equally complex RE
silicatesokanoganite,cappeleniteand steenstrupinewarranted the investigation.
0003-004)083/09
I 0-0996$02.
00
Cerites from several sources were studied. We thank
Messrs. John S. White, Jr. and Pete J. Dunn, U.S.
National Museum of Natural History, SmithsonianInstitution for cerite from Bastnis, Sweden(usxrvrR3925)and
Mountain Pass, San Bernardino County, California
(usNlvr117769);Dr. Carl A. Francis of Harvard Mineralogical Museum for Riddarhyttan, Sweden material
(HMM 86268); and Dr. John W. Adams of Lakewood,
Colorado for a related material from Jamestown.Colorado. The chemical investigation by Glass et al. (1958)
suggestedthat Mountain Pass material would be more
appropriatefor study than BastnSsmaterial. Dr. Howard
T. Evans, Jr. traced this original sample studied by Glass
et al. to the Smithsonianspecimen.A nearly equant grain
measuring0.(D x 0.11 x 0.12 mm from Mountain Pass,
California was selectedfor the ensuing study.
Precessionphotographs indicated good quality of the
996
MOORE AND S.EIEN: CERITE
crystal, and extinctions compatible with spacegroup R3c,
which is confirmed by the refinement of the structure.
The crystal data were collected on a Picker FAcs-l
difractometer with MoK" (I : 0.70926A)radiation. Cell
parameters refined on this instrument led to a =
10.779(6),
c : 38.061(7)4.With reflecrionsto 20 = 65',
scan speed2" min-I, base scan widths of 2" and background counting time of20 sec on each side ofthe peak, a
total of 7262 reflections was collected. No absorption
correction was applied, despite the relatively high linear
atomic absorptioncoefficientof about 131.70cm-r, due
to the absenceof regular crystal faces, the approximately
equant, isometric crystal shape and similar intensities
among equivalent reflections. From three to six equivalent reflections were averagedto obtain the independent
reflections. Caution should be applied to the refined
temperature factors since no absorption correction was
made. After Lorentz-polarization correction, a total of
171I independentlFol was obtained. The hexagonalcoordinate system was adopted throughout this study.
Statistical tests indicated a centrosymmetric structure.
However, we had already noted a close correspondence
between cerite and whitlockite, and decided to explore
the possibility of isomorphism, vz. the whitlockite data
obtained from Calvo and Gopal (1975).
addition, a partly disordered (SiO3OH) group, like the
(PO3OH)group along fi)z in whitlockite, was assumed.A
sequenceof site population and atomic coordinate refinements, followed by diference Fourier syntheses,led to R
: 0.095. Anisotropic refinement for all atoms associated
with rod ll at ryz and subsequentfull-matrix refinement
(excepting anisotropic thermal parametersalong fi)e) led
to R : 0.032 for all lTll independent reflections where
srlF"l *:ff.
lF"ll
The final cycle included 170variable parameters,giving
a variable parameter to data ratio of l0:1. The ssut-x-76
program systemwas used at the VAX computer facility of
The University of Chicago. Scattering curves for Ce3+,
Mg2*, Si4* and Ol- were obtained from International
Tables, vol. 4 (1974) and anomalous dispersion correction, f", for all metals from Cromer and Liberman (1970).
Atomic coordinate and anisotropic thermal vibration parameters are given in Table l, structure factor tables in
Table 2r and bond distancesand anglesin Table 3.
From the site population refinements in Table l, it
appearsthat all large cation sites are occupied by more
than one type of atom. The apparent site populations of
less than unity (relative to the Ce3+ scattering curve)
Cerite
Whitlockite indicate the presence of an additional element of lower
atomic number, which can be identified as Caz* on the
a(A)
10.78
10.33
basis of the chemical analysis(Table 5). Slightly decreasc(A)
38.06
37.10
ing site populations from RE(l) to RE(3) suggest that
S.G.
R3c
R3c
principally rare earths, and a lower Ca2+ content, occur
Formula (RE,Ca)q(Fe,Mg,Al)(SiOr)6(SiO3OH)(OH)3
at RE(l), with increasingCa2* at the subsequenttwo
CaeMg(POa)6(PO3OH)
n3,
sites. Since La, Ce and Nd are the principal rare earths in
Mountain Passcerite according to Glass et al. (1958),the
Solution and refinement of the structure
light rare earths evidently predominate in our sample.
Conclusionsregarding interpretation of Mountain Pass
cerite's chemistry were not made until appropriate conDescription of the structure
vergence of the structure refinement. Since the rule for
Cerite is based on the same structural principle as
isomorphismappearedto be RE3+Sia*s C** P5+,we
whitlockite.
The whitlockite structure was reported by
initiated the structure analysisby transferring coordinates
(1975) and was treated as a glaserite:
Calvo
and
Gopal
of Ca, Mg, P and O in whitlockite to Re, Mg, Si and O in
packing by Moore (1981). In the present
related
rod
cerite. At this stage, the role of C was uncertain for
Mountain Pass cerite, and we suspected its presence study, the atomic sites of Calvo and Gopal were assigned
would be indicated by short O-O distances(2.2-2.44\ simpler labels. The underlying features of the structures
(002)and rod II centeredat
consistentwith CO3groups or such short distanceswould are two distinct rods, rod I at
(Vst/62);the remaining rod locations in the cell are
ca.
be absent in the structure, in which case the (CO3)2group reported in the chemical analysis would be an determined by the space group R3c. For convenience,
impurity ion. Site occupancy parameters for the large these rods will be treated separately, then integrated to
cations (REE) and, subsequently,the disorderedatoms at define the structure. Rod II in particular defines a pin(X)zwere allowed to vary yielding R : O.23.Addition of wheel-type arrangement with circumjacent linkages by
(SiO+)tetrahedra. The unit fragment of rod II is featured
ten non-equivalentoxygensled to R : 0.17.
in Figure l.
A Fourier electron density map and subsequentdifference Fourier synthesis revealed substantial residues
along the fi)z rod. At this stage, and at any subsequent
rTo obtain a copy of Table 2, order Document AM-83-232from
stage of analysis, we failed to find any evidence for
the Business Office, Mineralogical Society of America, 20@
(COt2- groups. We assumedthese residueswere in fact
Florida Avenue, N.W., Washington,D.C. 20009.Pleaseremit
the water moleculesreported in the chemical analysis. In
$1.00in advancefor the microfiche.
998
MOORE AND S.EIEN: CERITE
Table l. Cerite: atomic coordinate and anisotropic thermal vibration (xlOa) parameterst
KX
RE(1)
RE(2)
R E ( 3)
0 . e 4 0 ( 5 ) 0 . 2 5 5 2 ()l
0 . 8 s 0 ( 5 ) 0 . r 4 3 s ( l)
0 . 8 7 9 ( 5 ) 0 . 2 5 e 2 ()i
si(r)
yz
utt
Uzz
U as
0.r318(r) 0.0583(2) 120(r3) il0(3)
e8(3)
0.2521(l) 0.4329(2) l r i ( 4 )
2e4(5) 1s8(3)
0 . 1 3 5 7 ( l ) 0 . 1 7 6 2 ( 2 ) r 60(4)
r46(4) il2(3)
Ur.
Urs
Uzs
-2(3)
17(21 72(3)
127(31 s2(4) l2s(4)
- 4 i( 3 ) - 3 7 ( 2 ) r 0 7 ( 3 )
0 .3 r5 4 ( 4 ) 0 . 1 4 7 1 ( 4 ) 0 . 3 6 4 r ( 2 ) 8 3 ( 1 3 ) r 2 s ( r 4 )r 2 8 ( r 4 ) r ( r 2 )
4(ro) 7't(12)
( r 4) 0 . 0 9 0 7 ( 1 5 )0 . 3 2 3 2 ( 3 ) 325(s0) 4 e 3 ( 6 0 ) 2 4 7 ( 4 6 ) -ls8(45)-'t27(41)2s4(461
0.26s3
0.2764(e) 0 . 0 0 3 4 ( e ) 0 . 3 8 7 1 ( 3 ) e ] ( 3 3 ) 1 r 7 ( 3 4 ) r 8 4 ( 3 s ) - 1 r ( 2 e ) l 3 ( 2 e ) 3 8 ( 2 8 )
0.2s78(12)0 . 2 4 7 8 ( 1 2 ) 0 . 3 7 e 5 ( 3 ) 23e(4r
l7(33) 4s(34)227(35)
) 228(40) 220(43)
0 . 0 8 5 7 ( 1 00). r 7 8 s ( r 0 ) 0 . 0 3 3 4 ( 3 ) r 2 1 ( 3 4 ) r o o ( 3 3 ) 2 4 4 ( 4 0 ) -+7(32l, 43(33) 44(2sl
0(l )
0(2)
0(3)
o(4)
s i( 2 )
0 .r 4 e e ( 4 )
0 . 2 4 1 s ()l l
-0.0r40(l0)
o .'r396
1 6 8(2e )
( l0)
0.
0(s)
0 ( 6)
0(7)
0(8)
M
r.460(8)
si (c)
0(e)
0H
0 . 8 6 2 ( 7 ) 0.0000
I
0 . r 6 0 2 [ lI )
0.866(e) 0.0000
0.0000
0 . 3 2 5 s ( 5 )0 . r 3 7 6 ( 2 ) e 3 ( 1 3 )
0 . 2 5 4 s ( 1 r )0 . 1 1 7 7 ( 3 ) l s l ( 3 5 )
0 . 2 5 4 0 ( r 00
) .r 2 3 5 ( 3 ) r 4 0 ( 3 5 )
0 . 0 7 4 3 ( i 0 )0 . 4 6 5 s ( 3 ) s 0 ( 3)1
0.2824(s) 0.r788(2) r28(33)
0.0000
0.0000
r 2 0 ( 1 4 )l l 5 ( 1 2 )
i(10) -s(13) 3(13)
1 7 5 ( 3 8 )l l s ( 3 s ) - 7 0 ( 3 0 ) - 2 s ( 2 s \ 4 l ( 3 1 )
l e 7 ( 3 e ) l r 0 ( 3 2 ) r 0 ( 3 0 ) - 2 6 ( 2 8 1 s 7 ( 3)r
5 4 ( 3)1 3 6 2 ( 4 6 ) 9 ( 3 3 ) - 4 8 ( 3)1 l 5 ( 2 6 )
r76(3s) 41(zel
3(26) 2e(28) 7e(30)
138(7e) 126(7s)r08(20)
5r(e3) -66(e2) -r5(80)
0.0000
0.2s24(2) 133(17) 133
5l(23)
0
0
57(9)
0 . 0 3 e 2 ( 1 20) . 2 3 e 8 ( 3 ) 1 5 0 ( 3 7 ) 3 7 0 ( s 0 )l e 2 ( 3 8 ) - 3 e ( 3 6 ) - 3 5 ( 3 2 ) l 2 e ( 3 5 )
0.0000
0.2957(5)3ll(s5) 3ll
148(57) 0
0
155(28)
0 . 0 e 7 ( 8 ) 0.0000
0.0000
0.0638(37)224(100)224
o
ilz(so)
80(ror) o
r
0.0000
0.0000
0.0e00(s) 5e(33) se
2so(62) o
0
30(17)
(e) 0 . 0 0 0 0
0H(3)
0.936
0.0000
0.r533(5) ll2(38) 112
o
s6(le)
2ro(5e) o
ca(x)
0 . 1 6 e ( e ) 0.0000
0.0000
0 . 3 4 4 4 ( 1 3z) s l ( 8 1 ) 2 s 1
32s(e2) o
o
r2s(40)
0H(2)
r
0.0000
0.0000
0.4090(5) 275(49) 275
137(24'l
208(64)
o
o
TEstirnated
s t a n d a r de r r o r s r € f e r t o t h e l a s t d i q i t . K . t h e s i t e m u l t i D l i c i t v . w a s b a s e do n c e 3 + f o r R E . M q z *
for-lil, Si{* for Si(c), Ca2+.for Ca(X) and 0r.- f6q the o,.ygens.. The a4isotro-pi^c..thennal
vibration parameteFsare
c o e f f i c i e n t s i n t h e e x p r e s s i o ne x p : [ { r r r h ' + U z z k z+ U 3 3 l , z " +2 U r 2 h k+ 2 U r g h C+ z u n k L ] .
0H(la)
oH(r)
The most intriguing feature of rod II is the oxygen
coordination polyhedra about the RE cations. If we
disregardthe RE-O bonds to anions along rod I, a direct
comparisonto whitlockitecan be made.RE(l), RE(2)and
RE(3) are in fact the samekind of polyhedra. Ideally, this
is polyhedronNo. 14 in Britton and Dunitz (9173)which
we shall call the D2d dodecahedron. It is one of 257
nonisomorphic polyhedra of order 8, and has No = 3
vertices,Nr : 18 edgesand Nz : 12facets.Constructed
of twelve regular triangles, it is a convex polyhedron,
with point symmetryD2d (4mD. In Figure l, the loci of
the 2-fold component of the pseudo-4axes for the three
successiveD2d d,odecahedraare presented. The central
RE(3)O8 polyhedron shares two edges with RE(2) and
RE(l) above and below. In addition, two more edgesfor
RE(3) are shared with RE(2), defining a shared face. In
both the cerite and whitlockite structures, the components of rod II appear to be the underlying basis of the
structure's stability and there is no evidence of disorder
in this region.
The situation is quite diferent for rod I, which appears
to be a more variable part of the structure. An excellent
survey of the whitlockite crystal chemistry was offered by
Calvo and Gopal (1975).As amplifiedby Moore (1981),
the structureis basedon a rod packingover the {6'3.6.3f
Kagomdnet. Rodsoftype II occur at the nodesofthe net,
and rods of type I occur at the centers of the hexagons.
Since the ratio of centersto nodes in the {63}net is l:2,
this meansthat the ratio of rod I:rod II : l:3. An outline
of the contents along the rod I axis at (002)is presentedin
Table 4, derived from the asymmetric unit contents in
Table l. Here, the coordinatefree variable(d andthe cell
population from refinement are listed for both whitlockite
(Calvoand Gopal, 1975)and cerite.Frondel(19a9)lists 11
chemical components in Palermo whitlockite; of these,
only 6 are in amounts greater than 0.5 wt.Vo. Calvo and
Gopal have shown that 4 are essential.The analysisof
Glass et a/. (1958)(Table 5) suggests10 componentsin
amountsgreater than 0.5 wt.Vo,with Ce2O3and the La2O3
rare earthstreated separately.The componentsin Table 5
have been grouped according to ionic radius. No evidenceof (COt2- groups was found in our study. Therefore, we assumedall COz reported in the analysiswas a
contaminant, specifically bastniisite. Subtracting 17.1Vo
CeLaFz(CO:)2led to column 2, which still possessesa
relatively large number of components, namely 8. From
this total, cation contents in the cell were calculatedfrom
our cell parametersand Glass et al.'s specific gravity.
Clearly the problem rests with the M site, where five
cations could play some role. In addition, about 5.5 H
atoms reside in the formula lunit (Z : 6), either bound as
OH- groups,neutral water molecules(HzO), hydronium
ions (H3O+),or any combinationof these.
Column 4 is particularly instructive. The sum of large
cations closely matches the theoretical limit for complete
cation occupancy in rod II. The octahedral cations total
to 1.55,in contrastwith I .00for the theoreticallimit. This
could mean either the presenceof impurities or additional
occupied sitesalong rod I. The tetrahedral speciessum to
6.79, where 6.fi) cations would constitute fully occupied
tetrahedra in rod II, and 0.79 would be the tetrahedral
fraction in rod I. The tetrahedral occupancy for Si(c)
refined to 0.86 at this site. The analysis and the assumptions madeby Glass et al. seemto be valid, with excellent
MOORE AND SfIEN: CERITE
999
Table 3. Cerite: bond distancesand anglest
RE(2)('3)
RE(l)
RE(r)-o(5)
-o(s)('g)
-01+1(')
-o(4)
-0101(')
-0121(")
-01r1('u)
-01s1(")
2 . 4 r 1 ( 7[ )
2.45s(7)
2'4s417)
2.505(7)
2'533(7)
2'62s(7)
2'824\7)
2 eo6(7)
n r 1 z 1 ( ' ) - 9 1 2 1 ( "2) 3 s 7 ( 7 1
-o(3)('3) 2'421(7)
-0121(t')2.46s(il
-o(7)(') 2.4s6(7)
-o(e)
2.sI3(7)
-o(l )
2.546(7',1
-01s1(") 2'5se(7)
-0101(") 2'87r(7)
Average
2,595 fi
Average
2.546
o(s)(")-o(z)(')
o1o1(")-s171(")
s171(')-s171(")
o(l)-o(5)(")
z.ss(zl
2.66(21
2.73(21
2.7s(21
60.3(3)
s9.l(3)
65.5(3)
64.8(3)
m 0(l)-0(e)
o(r1-e171(')
o(s)('?)-o(e)
o1z1(")-9171(")
m o(l)-o(7)(")
6131(")-e171(.)
o{e)(")-0,n,
no1r1(")-s171(rr)
3.32(2)
3.33(2)
3,34(2)
3.42(21
3.4s(21
3.65(2)
3.79(3}
l,st(+)
82.1(3)
82.7(3)
Bo,4(3)
89.s(4)
88.4(4)
e5.8(4)
se,2(4)
134.6(5)
o 1 z 1 ( " ) - e 1 a 1 ( " z) . 5 5 l z )
si(i)
si[1) r o(3)(rq)-0(4) 2.sl(z)
o(3)(")-o(e)(") 2.Brtzl
r
o1+1-61a1(') 2.8s(2)
o 1 z 1 ( " ) - 6 1 u 1 { ' )z . t ' r t z )
"
RE(3) otsl-6J61(')
2.s2t2)
o 1 z 1 ( " ) - e 1 6 1 ( "2) . s 6 ( 2 )
t o 1 e 1 ( ' ) - s 1 e ; ( " )z . s t ( z l
o 1 : 1 ( ' n ) - 6 J s 1 ( '3) . o o ( 2 )
( ,' )
3 .r 8 (z)
o 1 : 1 - s 151
n o 1 + 1 ( ' ) - 9 1 6 1 ( ' )3 . 1 8 ( 2 )
3,24(2)
o(4)-o(e)t't
n o(5)-o(9)(1r) 3.34(2)
3.s2(2)
o(4)-o(5)
o 1 + 1 ( ' ) - e 1 6 1 ( ' )3 . 8 4 ( 3 )
o 1 e 1 ( ' ) - 6 1 9 1 ( " )3 . e 7 ( 3 )
("
("
o 1 z 1 ) - 6 1 9 1 ) 4 .l l ( 3 )
4.s9(4)
n o(4)(')-o(s)
Average
3.25
59.7(3)'
5 7 . 3 ( )3
58.7(3)
si(z) r
si(2)
il
ob.olJj
72.5(3)
7r.r(3)
6 6 . 63( )
6 8 . 93( )
7 0 . 5( 3)
80.r(3)
1 7. 2 ( 3 )
er.6(4)
9 9 . 84( )
e3.6(4)
e5.7(4)
138.6(5)
79.0
79.3
Average
3.20
3 u-o(z)(")
3 -0(4)
2 . 0 4 9l(o )
2 . 0 9 6l(o )
Average
2.072
R E( 3 )
('?
RE(3
) -o(6) )
-0(8)
-o(3)(!)
- 0 1 2 1 ('' )
- o ( e 1( z)
-0(e)
-0(s)
- 0 1 11( " )
Average
si(2)
si(t)
si (2)
0(3)(")-o(el
0(s)-0(6)1"
o{21(")-ott'
(')
o { e 1 - o tn '
RE(2)
o1z1(")-e13y(')
m 613y(")-e1sy(')
RE(z) r o(2)(")-o(s)
m o1t;(")-0,t,
o(8)-o(e)
o1:1(')-e161(')
o1t1(")-6151(')
m o(l)('r)-o(3)('g)
o(s1-6161(")
n 0(s)-0(8)(')
Average
R E ( 2 )3 o ( 7 ) ( ' ) - o ( 7 ) ( n )
2.640(7)
2.669(7\
nr(r) s o(q)-o(c)(')
I o1+1-0171(')
: o1c1-6171(')
2.610
cley(')-6161(') 2.62\2)
oJtl(")-s121(")
0(5)-0(8)
2.64(2')
(' ') -ott
? 77(2\
o{tI
'
RE(2)
RE(l) r
fEstlmated
2 . 4 5 (77 1
2.492(71
2.s40(1)
2.549(7\
2 .582(7)
2.81(2)
2 a2l2\
3 . 0 02( )
3 . 0 r( 2)
3.42(2)
4 . 0 33( )
4 . 0 5 (3)
4 . 5 73( )
4 . 5 73( )
3.29
2.73(2)
2.89(2)
3.02(2)
3.08(2)
90.0'
Average
62.6(3)
5 6 . 6( 3 )
61.4(3)
s8.7(3)
6s.6(3)
5 8 .e ( 3 )
7r.e(3)
59.r(3)
7r.8(3)
7r.0(3)
77.2(4)
88.7(4)
e3.7(4)
es.e(4)
e4.6(4)
| 2 0 . 5 ( 5)
r28.3(5)
83.4(6)
87.0(5)
e3.s(6)
e6.r(5)
si(r)
si(l)-o(4)(')
-o(3)
-o(2)
- o ( r)
l.6oe(8)
r.5r5(8)
r.538(8)
r .662(8)
Average
1.531
RE(r)
RE(r)
RE(3)
o(2)-01+1(')
o(3)-o(4)(')
o(r)-o(2)
0fi1-91a1(')
0(2)-0(3)
o ( r) - o ( 3 )
2.55t2)
2.s8(2')
2.6312')
2'6s12')
2.76121
2.76(2)
103.6(5)
r05.7(s)
ros.8(s)
r r0 . 7 ( 5 )
lls.7(5)
1r4.7(s)
Average
2.66
I09.4
79.3
standard errcrs in parentheses refer to the last dlgit.
The equivalent positions (referred
deslgnatedas superscripts and are (l) = -J, x-J, 71 (ll = y-a, -x, z; (3) = -y, -x, hrz; (4) - x, x-y,
(b.l = 2/3+x, r3+y,.r,3+z; 17) z,s-y, t.3+x-y, r/1+zi (Bl = ut+y-x, L/1-x, r2r+z; (91 = 24-y, L/r-x,
I r+x-y;.:(G+z; (fll = 2.3+y-x, r.3+y,.s/6+zi 112)= t4+x,2,.+y, z4+zi (13\ = r/3-y,2,r+\-y,2/r+zi
2 i+z; (f5J = r,3-y, 2 3-x, r/5+z; (16) = r/3+X, 2.!+x-yt r/6+zi (17) = r,3+y-x, 2..+y, r,6+2,
to Table l) are
t+z; (5) : y-t, y, \+z;
s/6+zi (t0) = 14+x,
(141 -- r4+y-x,2/r-x,
Cations which share polyhedral edges are noted on the left.
Ridgepole (= r) and reridional edges are also noted.
that RE-{H(1,2,3) distances are listed under 0H(1,2,3) and are not included ln the RE-{ bond distance averages.
Note
I000
MOORE AND SHEN: CERITE
Table 3. (continued)
si(2)
si(z)-61s;(s) r.620(8)
_o(s;(s) r .623(8)
- o ( z()u)
r.528(8)
- o ( s(1' )
r.535(8)
R E ( 2 ) o 1 s 1 ( ' g ) - 9 1 7 12( ". 5) s ( 2 1
RE(3) 6161(')-s1g;('2
) .62(21
R E ( 3 ) o { s y ( ' ) - e 1 s 1 ( ' )2 . 6 4 ( 2 )
RE(z) o1o1(')-e171(u
2 .) 6 6 ( 2 )
s l z y ( u ) - e 1 s 1 ( ' 2) . 6 s ( 2 )
e 1 5 1 ( ' ) - s 1 6 1 ( '2) . 7 6 Q )
Average
2.66
I 0H(2)-ca(x) 2.46(5)
-RE(2) 2.6r(r)
-0(7)
3
2.66(21
I 0H(l)-0H(la) r.oo(r4)
- R E ( r)
3
2.s2(1)
-0(4)
3
2.72(2)
-0H(3)
2.7s(2)
I
1.627
Average
o H( 2 )
0H(l)
3
oH(la)
3
109.5
1 oH-si(c)
'| -Ca(x)
3 si(c)-0(e)
-0H
r
1.686(7)
Average
L645
3 0(e)-0H
3 o(e)-o(9)(')
2.67(2)
?.70(z)
107.1(5)
'nr.7(s)
Average
2.68
109.4
3 oH(3)-RE(3) 2.47(4)
-0(8)
2.70(sl
3
I 0H(la)-0H(l) r.oo(r4)
-0(4)
2 . 0 3s()
- R E ( )l
3
2.3e(4)
r05.7(5)
r07.2(s)
107.6(5)
loe.0(5)
111.5(s)
lls.8(6)
si(c)
0H(3)
r
- o H () r 2 . 7 s ( 4 )
2.43(5)
l-M
ca(x)
OH
3
-o(e)
3
-o(r)
r ca(x)-oH
-0H(2)
1
-0(r)
3
-0(3)
3
r.6s(2)
r.82(5)
2 . 6 7( 2 )
2 . 7 r( 3 )
l.82(s)
2.46(s)
2.54(4)
3.04(5)
1.631(8)
agreement for large cation contents and supports the
subtractionof bastniisiteas an impurity phase.The role of
H2O remains a problem.
Mg2* is the predominant octahedrally coordinated cation which could reside in M, but Al3* and Fe3+ are also
present in substantialamounts. This site is believed to be
Table4. Cerite:cell contentsalongrod I at 002,etc.t
Cerlte
lhltlGklte
X
t't
o(l)
0.000
6.00
.10
.re3
o(lA,)
P(A')
o(rA)
.298
Ca(IIA')
o(2)
.312
.4tl
0.000
ofl(l a)
l.l4
'1.'t4
.234
.25s
P(A)
14
4.86
4.86
0.57
o H ( l)
0lf(3)
si(c)
0H
Ca(x)
0H(2)
,064
.090
. 163
.252
.297
.344
.4(D
8.76
0.58
6.00
s.62
5.17
5.20
l.0l
6.00
xy
0 ( r r A ' ) 0 . r 3 8 0 . 0 0 0 0.250
Fig. l. Cerite: unit of rod II showing REO3D2d dodecahedra,
loci of pseudo 2-fold (D axes and circumjacent SiOotetrahedra.
Atoms are labelled according to Table 3. The drawing is a
Penfieldprojection.
0(IIA)
.r50
.0r9
3.43
.242 14.57
0(9)
.160 .039 .240 18.00
rThe atm labels in Calvo and Gopa'l(1975) for whltlockite and cerite in
this study are retaired. The variable parmter, !, in 0 0 z is listed.
The ell amtents are listed under K. tlote that Ffor ll was-basedon the
icattering curve for llg2'.
MOORE AND S.T-IE.N..
CERITE
1001
lCa(x),OHl relationship is suggested.Indeed, adding
their site populationswe get 0.17 + 0.87 : 1.04.This sum
12
34567
could easily be reduced to 1.00 if some RE cations
substitutefor Ca(x). In fact if Ca(x) = Cer*, the site
35.05 3.90 I
9
73.36
35.6r
Cezoe
35.73 29.08
30.08
1 a 2 0 3e t c .
31.53 24.93
30.04 3.37 |
populationwould be approximately0.06. OH(2), which
4.49
3.72
3.72
4.48 1.45I 6
^ ' ^v ^o
Cao
0.37
0.45 o.o5 (
0.42
Bao
0.37
was assumedfully occupied, roughly matchesthe vacant
0.24 o.l4 |
0.24
Na20
0.20
0.20
0.16 0.06 t
0.16
KrO
0.13 0.13
position,tr(2), in whitlockite,just as OH(1) approximates
't.58
n(1). OH(3) approximatesthe P(A')-O(1A') positionsin
1.35
t'lS0
1.58
r.e0 0.86 |
lln0
0 . 1 7 0 .1 7
0.20 0.0s I
which are evidently absentin cerite.
whitlockite
Alz0s
0.95
0,95
r.r4 0.4r I r.5s
Fe203
3.96
l.7r
0.76
0.76
0.92 o.2l I
A neat interpretation can be effected which exploits
Ti0z
0.07
0.07
0.08 0.02 |
some geometrical properties of the DZd dodecahedronof
C0z
3.56
8 discussedin this paper. We recall that all three
order
20.89
22.49
Si0z
I 8.46 I 8.46
2 2 . 2 4 6 . 7 6 l 6- 7
" '0
S0r
0.12 0.12
0.14 0.03 ,
0.13
non-equivalentRE positionsresidewithin the samekind
of polyhedron, illustrated in Figure 2. Although this
F
1,60
0.05
0.07
HzO(-)
0.14 0.14
0.17
polyhedron can be constructed with l2 equilateral trian1.79
3.32
tfz0(+)
2.26
2.26
2.72 5.53
-0.67
gles, four pairs of such triangles are nearly coplanar and
0 . 2F
't00.00
define rhombi, where two triangles sharean edgedefining
Total
100.68 83.00
100.00 100.00
the short diagonalofthe rhombus.Therefore,the polyher c l a s s e t a l . ( 1 9 5 8 )o n l ' l o u n t a l nP a s sn a t e r i a l .
dron can be consideredas constructedfrom 8 vertices;4
2 ( l ) l e s s 1 7 , 7 1b e s t n a s l t e ,C e L a F z ( C 0 r ) a2 s, s u m i n tgo t a l c o n t r i b u t i o n s
equilateraltrianglesand 4 rhombi; and 14 edges.
t o C 0 z . T h e C e : L a= 1 : l r a t i o w a sa r b i t r a r i l y s e l e c t e d ,
The anions situated on rod I along 00e bear a one-to3colw 2 renomalized to 100.001.
one
correspondencewith each of the three non-equivaqcalculated
c a t i o n s l n f o m u l a u n l t . Z = 6 . T h i s d e r i v e df r o n c o l u m 3 ,
lent
RE cationsand bond to them. For example,RE(l)gravity
paraneters
in
Glass
the specific
of 4.78
et al. and the cell
reported in this study.
OH(!) : 2.52, RE(2)-OH(2) : 2.6r and RE(3)-OH(3) :
s l d e a l a t o m l cc m t e n t s , f o r R E t + F e 3 + ( S i 0 q ) 6 ( S i 0 3 0 H ) ( 0 H ) 3 .
2.47A. Since these OH sites are largely occupied and
6cmputed formula basedq colum 5, with RE3+= Ce3*.
since three RE atoms bond to each OH(I,2,3) on the 3Tcmputedfomula basedm (A) in the text.
fold rotor, the OH(1,2,3) groups are electrostatically
neutral. Furthermore, it is logical to propose that Fcerites should exist. With the addition of the OH(1,2,3)
fully occupied; although we employed a scattering curve ligands,the coordinationnumber increasesto 9 for each
for Mg2*, the site population refinementgave 1.46 Mg non-equivalent RE cation. The greater bond strength of
atoms per site (Table l), suggestingthe presenceof a RE3+-O comparedwith Ca2*-O appearsto be the decidheavier cationic species.We propose that the first series ing factor in the incorporation of additional (OH)- ions
transitionmetalcations,most notablyFel' . partitionat into the coordination sphererelative to the Ca-O polyhethis site. The site populationrefinementsuggestsca.0.39 dron in whitlockite. This phenomenon may explain the
Fe3* at this site. This would yield an average great diversity of exotic RE silicates compared with the
tot(tr,tgo2irFe3.1sFO
: 2.09A distance, close to 2.074 in Ca phosphates.
Table 3 for this site.
The mode of the additional bond is very interesting: in
The distribution of atoms along rod I at 002 is summarized in Table 4. Splitting of Si(c) into two parts such that
their total equals I is evident in whitlockite. For cerite,
we could not find evidence for a corresponding splitting,
becausebut little residual electron density would remain
(0.83/6x 14 = 1.9 electrons)and becausecerite includes
major lanthanideions. In the absenceoffurther evidence,
we prefer to accept the theoretical formula for cerite in
much the same senseas the complementary relationship
between P(A) and P(A') in whitlockite. The OH(la)OH(1) distanceof 1.00A suggestsa cooperativerelationship. Although our refinement assumedsite population of
1.00for OH(l), OH(la) refined to site population 0.10.
We suspectthat OH(l) is probably reducedto site population 0.90. OH(3) has site population0.94. This site may
indeed be fully occupied. Ca(x) closely matches the
B
A
position for Ca(IIA') in whitlockite. It is only weakly
populated in cerite, as it is in whitlockite. The Ca(x)-OH
Fig. 2. Penfield projections of(a) the D2d gable disphenoid and
: 1.824 distance is short and therefore a cooperative (b\ the D2d dodecahedron. Both polyhedra are of order 8.
Table 5. Cerite: chemical analysis and interpretation
1002
MOORE AND STIEN.. CERITE
Table 6. Cerite: electrostatic valence balance of cations and anionst
C o o r d i n a t i n gC a t i o n s
Anions '"'*t1t1'*
0 (l )
0 ( 2)
0(3)
0(4)
ttlRE(z)t*
"'*r1r;,*
+0.000
-0. t49
+0.343
-0.06t
+0.229
- 0 .I 0 l
-0.090
-0.125
-0.070
0 ( s)
0 ( 6)
0 ( 7)
-0. I 84
+ 0 . 11 3
+ 0 .3 2 5
-0.081
-0.050
0(8)
- 0 . 14 0
0(s)
OH
+0.3lI
0H(l)
oH(2)
0H(3)
;; ;;,
-0.052
Es3rr+ tulsi(l)u*
+0.024
apo
+ 0 . 0 31
-0.33
+0.007
- 0 . 0 15
+0.00
+0.00
- 0 .l 7
-0.022
+0.059
-0.004
+0.00
.1ll'
+0.009
+ 0 . 0 0t
+0.00
-0.17
-0.007
- 0 .3 3
-0.I18
-0.028
-0.033
c"lSi121u* t.lSi(.)**
+0.030
-0.023
-0.014
+0.041
3 x (- 0 . 0 7)
+0.00
+0.00
+0.00
3x(+0,06
)
+0.00
3 x (- 0 . I 4 )
+0.00
tA bond
length d e v i a t i o n r e f e r s t o t h e p o l y h e d r a l a v e r a g es u b t r a c t e df r o m t h e i n d i v i d u a l b o n dd i s t a n c e .
RE averagesin r a D r eJ w e r Et a k e n . T h e A p o = d e v i a t l o n s o f e l e c t r o s t a t i c b o n ds t r e n q t h
s u mf r' o- "m
n e u t r a l i t y ( p o = 2 . 0 0 e . s . u . ) . T h e i d e a l i o r m u l aR E g + F e 3 . ( s i 0 * i " ( s i 0 ; 0 i i t o i l-.i i - l d i ! . i i J .
t8lce3+-t3.slo2: Z.S1A, t81la3+_t3.51o2: 2.55A and
t81ca2+_t3.51o2= 2.494. The mean t8tRp(t)_O: 2.60,
t8rRE(2FO: 2.55 and t8lRE(3)-O= 2.6ll for the oxide
fraction in Table 3 are all slightly larger than these values,
but relatively few data comprised the Shannon and
Prewitt tables, and none represent silicates. The ditrerences,however, are very small. In addition, our cerite
apparently contains a wide range of different ions in
solutionat these sites.
Bond length-bond strength electrostatic valence balances are tabulated in Table 6. Here some drastic assumprionswere made. First, the ideal REf+Fe3*1sior;u
(SiO3OH)(OH)3formula was invoked. Second,since H(ceitor-d*. *tCa?7ts4.tsNai.1oKJ.&)>:r.r,
positions could not be located, the (OH)- ions were
(S{.trs8ir)>:o ao(Mgo
treated as fluoride ions, for example. Some guessescan
u,Fe3.1q)>:
r oo
be made about the behavio-rof the protons from Table 3.
(A)
Cdjrorr68(oH)0.86(oH)3 03
The OH(I)'-OH(3) : 2.79A distancesuggestsa possible
and suggestsan ideal end-memberformula REa+Fe3+ symmetricalbond. The OH(IFO(4) :2.724 and OH(3I(SiO4)6(SiO3OH)(OH)3.
The Fer+ content required by
O(S) = 2.70Aare also possible.Here, the protonswould
this formula is admittedly higher than that reported in
be tightly constrained on the 3-fold rotor by the oxoanTable 5, columns 3 and 6, but presently we see no
ions in generalpositions,or they may be disorderedinto
superior explanationof the high site multiplicity (1.46, three pieces. Likewise, OH(2FO(7) = 2.664,could bebasedon Mg2+ scatteringcurve: c/. Table l).
have the same way. Finally, the OH-O(9) : 2.674 or
With three additional anions in the formula unit over OH-O(l) = 2.714 bond could exist, the former unlikely
total anions in whitlockite, cerite is an efficiently packed becauseit is a SiO3OH tetrahedral edge. The uncertainty
structure indeed, with V6 : 20.5943per anions, rivalling
in the role of the protons forces no conclusion on the
the densestoxysaltswhich are derivedfrom the glaserite OH- ions in Table 6 since the O-H distancesare not
structure type.
known.
With theseassumptionsin mind, nine anionsare elecElectrostatic valence balances and bond distances
trostatically neutral, four are electrostatically undersatuFrom the effective ionic radii of Shannon and Prewitt rated. The polyhedral averageswere those taken for the
(1969),the averagebond distances are anticipated to be anhydrous RE-oxide bonds in Table 3. Since the svstem
each case, the bond is through one of the rhombi. The
rhombi in question are O(4)(2)-O(4)-O(5)-O(6)(t)fot
RE(l); O(A(tt)-O(7)(rr-913;er-912)(rt)
for RE(2); and
O(8)t2r-916;rzr-O(A)-O(S)
for RE(3). In each case, the
short diagonaledgeofthe rhombusis openedup in cerite,
viz. O(4)@-O(5): 4.59 for RE(l); O(3)ter-612rt]o
: 4.51
for RE(2); O(8)-O(8)(2)= a.574 for RE(3). These are
comparedwith edgedistanceaveragesof 3.2-3.44 for the
D2d dodecahedronin cerite (Table 3).
Summing up, accepting a// sites, occupanciesand
chemical analysis, our crystal formula can be written for
Z: 6:
MOORE AND SHEN: CERITE
t003
Frondel, C. (1949)Wolfeite, xanthoxenite and whitlockite from
the Palermo Mine, New Hampshire. American Mineralogist,
34,692J05.
Glass,J. J., Evans, Jr., H. T., Carron, M. K. and Hildebrand,
F. A. (1958) Cerite from Mountain Pass, San Bernardino
County, California. American Mineralogist, 43, 46U475.
International Tables for X-ray Crystallography, Vol. 4. Revised
and SupplementaryTables(1974).Ibers, J. A. and Hamilton,
W. C., eds., Kynoch Press,Birmingham.
Acknowledgments
Jorpes,J. E. (1966)Jac. Berzelius:His Life and Work. (Transl.
Severaldonorsof specimenswere noted in the text. PBM
by B. Steele),Almqvist and Wiksell (Stockholm).
grantandJ.S.theMinistry Moore, P. B. (1981)Complexcrystal structuresrelatedto glaseracknowledges
theNSFEARSI-21193
ite, K3Na(SOa)2:evidence for very dense packing among
of Education,thePeoplesRepublicof China.Wejoin in thanking
oxysalts. Bulletin de la Soci6t6Frangaisede Min6ralogie et de
Dr. Joseph
J. Pluthwho assisted
in variousstages
ofthis study.
Cristallographie, 104, 536-547.
References
Shannon,R. D. and Prewitt, C. T. (1969)Efective ionic radii in
oxides and fl uorides. Acta Crystallographica,825, 925-946.
Britton,D. and Dunitz,J. D. (1973)A completecatalogue
of
Shen,
J. and Moore, P. B. (1982)Tornebohmite,RErA(OH)
polyhedrawith eight or fewer vertices.Acta Crystallogra[SiOr]z: crystal structure and genealogyof RE(III)Si(IV) e
phica,429,362-371.
Ca(II)P(V) isomorphisms. American Mineralogist, 67, l02lCalvo,C. andGopal,R. (1975)
Thecrystalstructure
of whitlock1028.
ite from the
is extensively neutral locally, negative deviations tend to
be compensatedby positive deviationsin the samerow.
O(8), with Apo = -0.33, has shorter bonds than the
average.The only exceptionis O(l), with Apo = -0.33.
Here all bonds are longer than average. We suspect a
disorderedOH-O(l), possibly a disorderedsymmetrical
O-H-O(I) bond may account for this contradiction.
PalermoQuarry.AmericanMineralogist,
60, 120133.
Cromer,D. T. andLiberman,D. (1970)Relativistic
calculation
of anomalous
scatteringfactorsfor X-rays.Journalof ChemicalPhysics,
53,1891-1898.
Manuscript received, September l,5, 1982;
accepted for publication, March 8, 1983.