Download The Fe2+r(HrO)"[POn], Homologous Series. II. The Crystal Structure

American Mineralogist, Volume 60, pages 454-459, 1975
The Fe2+r(HrO)"[POn], Homologous Series.
II. The Crystal Structure of Fe2+s(HrO)[pOn],
Pnur-Bntc.NMoonn, eNo TnrnHnnu Anerr
Departmentof the GeophysicalSciences,The UniuersityoJ Chicago,
Chicago,Illinois 60637
Abstract
Thesynthetic
compound
Fe'z+s(H,O)[pOr],
hasa 9.a31(l)A,,10.066(l)A,
c g.040(l)A,0
117.632('7)',
P2'/a,Z : 4. lts structure,
refinedto R(hkl)= 0.068lor 2457independent
reflections, consistsof complex open framework formed by edge-and corner-linking of distorted
Fe(1) and Fe(3) octahedra,ofdistorted Fe(2) polyhedra offive-fold oxygen coordination, and
of POn tetrahedra.Average bond distancesare Fe(l)-O,2.16 A; Fe(2)-O,2.08 A; Fe(3)-O,
2 . 1 5 A ; P ( l ) - o , 1 . 5 5A ; a n d P ( 2 ) - o , 1 . 5 4A . U n u s u a l f e a t u r e so f t h e s t r u c r u r ei n c l u d e a
Fe(2)-P(2) 0(6)-0(8) 2.41 A shared edge; and a Fe(2)'-ps12;'O(4)-O(4)r 2.63 A shared edge.
It is proposedthat a bounded oxidative sequencemay exist for the crystal,where Fe(l)r+ Fe(1)3+and HzO - OH-. The limiting formula lor a stable oxidized crystal would be
Fe", Fe'-(OH)[PO.]r.
Introduction
a , 0 . l l m m a l o n g b , a n d 0 . 0 4m m a l o n g c w a s s e l e c t e d
for intensity measurements.The compound is pale
The homologous seriesFe2+s(HrO)o[pOo],
includes green in color, with crystalstabular parallel to {001}
severalcompounds where all water moleculesand all and striated parallel to [100]. Figure I features an
phosphate oxygens are also bound to the transition idealized sketch of typical development of the crystals.
metal. Well-characterized natural compounds inSuccessive
shellsof reflectionswere gatheredto sin
clude vivianite and metavivianite (r:8), ludlamite d/I : 0.8 on the Plcrnn diffractometerwith MoKa,
(n:4), phosphoferrite (n:3), sarcopside and graf- radiation and graphite monochromator. Full scans
tonite (n:0). In addition, severalrecentlysynthesized ranged from 2.4" at the lower levels to 2.8' at high
compounds have been brought to our attention, in- angles with a scan speed of 2" /minute. Twentyc l u d i n g t h e s u b j e c to f t h i s s t u d y , w h e r e n : 1 .
second background measurementswere taken on
each side ofthe peak. The data were processedto obExperimental
tain F(obs) after applying an absorption correction
Single crystals of Fe2+r(H2O)[PO4],were synthe- by the Gaussian integral method described by
sized by Dr. E. Mattievich at 230.C and 400 bars Burnham (1966). All 2457 independent reflections
pressure,using a hydrothermal technique with syn- were acceptedfor the ensuing study.
thetic vivianite as starting material. Dr. Mattievich
Structure Determination and Refinements
informs us that wet chemical analysesclosely conform with the ideal formula and that Mossbauer
The Patterson synthesis,P(uuw), revealedthat all
resonancestudies have been performed on the com- metals reside in general positions, requiring coorpound.
dinate determination for Fe(l), Fe(2), Fe(3), P(1),
Preliminary single crystal Weissenbergand preces- and P(2). Several minimum functions provided unsion photographs establishthe spacegroup and cell ambiguous location of the metals which afforded
parameters,the latter refined by twelve reflectionson sufficient scattering matter for a
B-general synthesis
the Ptcran four-circle automated diffractometer.The as described by Ramachandran and Srinivasan
r e s u l t sa r e a 9 . 4 3 1 ( l )A , b 1 0 . 0 6 6 ( t )A , c 8 . 0 4 0 ( l ) A ,6 (1970). The ensuing map revealedall non-hydrogen
117.632(7)', space group P2r/a, Z : 4. A powder atom locations without difficulty.
pattern, indexed with the aid of the single crystal
Full-matrix least-squares refinement, including
d a t a , a p p e a r si n T a b l e l .
scale factor, non-hydrogen atomic coordinates and
A superior singlecrystal measuring0.09 mm along isotropic tlrermal vibration parameters with 2457 in-
455
CRYSTAL STRUCTURE OF Fe'+" (H,O) [PO^],
TnsI-e I
I/Io
d(obs)
d (calc)
70
20
40
20
10
100
15
20
l5
10
15
45
5 .81-0
4.146
4.097
5. 8 1 4
4.ls5
4.100
3.730
3.561
3.357
3.035
2.992
3. 5 5 3
3.351
3.030
2.984
2.903
2.722
2 . 68 0
2.655
2 0l l
2.729
2.687
2.659
Fe'(H,O)[PO.],.PowderData*
l/Io
011
r21
rIl
112
002
012
031
311
2TI
tl_2
131
3zr
20
40
5
20
5
30
IO
20
10
10
l0
15
d(obs)
d(calc)
2. 611
2.57L
2.5L2
2.469
2. 4 3 5
2.378
2.32t+
2.039
2.003
1 . 8 94
1 . 83 3
1.801
2. 6 1 6
2.573
2.5L7
)
230
z!J
0r+0
T2?
320
313
tr71
2.437
2.384
2.328
2.0q5
2.008
1.896
l_.835
l_.805
LZJ
r+10
204
123
3zq
Izq
ot)
*Powd.en
Si (g = S.+SOf -E; intern-ral.
Iolminute, CuKc radiation,
diff ractogram,
and cell parameters
I n d i c e s a r e b a s e d o n strong single crystal- reflections
stated
in
the
text.
dependent reflections converged to
R(hkl)
known structure. There are feeble resemblancesto
: 0.068.
For the other members of the homologous series,and these
>llr(obs)l- lr(calc)lll>lF(obs)l)
relationshipsshall be emphasized.
To appreciatethe problem more fully, we rewrite
which consists of
the formula as a cluster I,1z+252+A",
three divalent transition metals-two octahedrally
coordinated (= M) and one five coordinated (=
S)-and nine oxygen-ligandvertices,A, pet formula
unit. Characteristic of the homologous series
Fe2+a(HrO)o[PO, ]r, all n-w ater mo leculesare aquated
(are found as ligand groups) to the transition metal
and all oxygensassociatedwith the [POn]'- ligand (:
Descriptionof the Structure
Op) are also bound to transition metals.
In a detailed study on this homologous seriescerTopologyand Geometry
among these structures
is com- tain common characteristics
The crystalstructureof Fe2+s(HrO)[PO'],
the
As r decreases,
(Moore,
l97l)'
were emphasized
plex, and bears no obvious relationshipwith any
polymerization
or
degreeof octahedralcondensation
increases:for n : 8 (vivianite), the octahedral com-
1569reflectionsexceedingthree times the estimated
backgrounderror,R(hkl) : 0.039.Estimatedstandard errors in distancesare Me-O + 0.004A and
curvesfor Fer+,Po,and
O-O' + 0.006A. Scattering
01- derive from the tablesof Cromer and Mann
( l 968).
Final atomic coordinateparametersappear in
Table 2, and the structurefactor data are presented
in Table3.'
T,qslr 2. Atomic Coordinate and Isotropic Thermal
Vibration Parameters for Fea(HzO)[PO.L+
Bd2)
AB
Frc. 1, Typical crystal of Fe2+r(HrO)[PO.], showing the forms
c { 0 0 1 } ,u { 0 l l } a n d r { 2 0 1 } . A . P l a n ; B . C l i n o g r a p h i c p r o j e c t i o n .
I To receive a copy of Table 3, order document number AM-75003-A from the Businessoffice, Mineralogical Society of America,
1 9 0 9 K S t r e e t ,N . W . , W a s h i n g t o n , D . C . 2 0 0 0 6 .P l e a s er e m i t $ 1 . 0 0
for the microfiche.
0 . 8 2( r )
. 6 9( D
.6r(r)
.4386(1)
.28r3(r)
0.13se (1)
.877r (r)
.r241 (I)
0 . 4 1 3 0( 1 )
. 0 7 4 e( I )
.2628(1)
P (1)
P (2)
. 6 7 4 0( 1 )
. 1 3 + 3( 1 )
.087 3 (l-)
.8320 (r)
. 3 7 8 6( 2 )
.0262(2)
. 4 e( 2 )
.ss(2)
o (t)
o (2)
o (3)
o (4)
. 8 03 s( q )
. 7 4 8 5( 4 )
. s 4 3 0( 4 )
q q q ?r u \
.1876(4)
- n)o2 (u\
.1s66 (4)
.0308(t+)
.3e50(s)
.sL72(s)
.'tllo(s)
. 1 7 4 7( s )
.72(s)
. 6 7( s )
.78(s)
. 7 e( s )
Fe (1)
Ie (2)
Ee(3)
o (5)
o (6)
o(7)
o (8)
OW
*Estimated
0.03rs(r)
-.0r88 (r+)
. 2 5 3 3( r + )
. 0 e 0 9( 4 )
.23r+2(r+)
errcrs
refer
- . 0 2 s s( s )
. 8 4( s )
. 7 8( s )
. e 1( 5 )
.8I (s)
. 6 8 + 0( s )
. e 8( s )
.rrr3 (s)
.L723(5)
.082s (r+)
.07Is(4)
standard
- . i l + g r( 5 )
.8713(4)
. 9 r + 9 7( 4 )
. 7 7 r + o( 4 )
. 7 3 2 8( 4 )
to
the last
digit.
456
P. B MOORE, AND T, ARAKI
bination includes the edge-sharingdimer M"ero I
the monomer MQu : MrQrr, which is equivalent to
the expressiondr. : (HrO), + (Op)r. For n : 4
(ludlamite) the cluster formula ts Mrerrand the structure contains corner-linked chains of Mrern linear
edge-sharingtrimers bridged by the [POn]tetrahedra.
For n : 3 (phosphoferrite),theselinear edge-sharing
trimers MrS, fuse by further edge- and cornersharing to form Mr@r, sheets.For r = 0, one of the
dimorphs is sarcopside(c/Moore, 1972)which is an
ordered derivative of the olivine structure type. With
the cluster formula Msg",we observethe same linear
edge-sharingtrimers as the structural motif. Since
Fe2+, (HrO)[PO.], is compositionally wedged in
between,we had anticipated that it, too, would possessthese linear edge-sharingtrimers.
The Fer(HrO)[POn],structure not only revealsthe
absenceof such linear trimers, but also provides two
kinds of oxygen coordination about the transition
metals; two distorted octahedra and one very distorted tetragonalpyramid! In addition, this awkward
structure has resistedany obvious vehicle of description, and we despairedof finding a suitableprojection
until we selecteda projection down a' : a - c, showing the plane b X c' sin p', wherec' : a I c. A slab of
the structure, where the transition metal coordinates
are bounded by Vo< x' I t/2,is provided in Figure 2.
This projection, which features the transition metal
polyhedra only, has advantagesin that all three nonequivalent metals can be referred to a common level
in x'. At x' : t/2,the polyhedra are stippled,revealing
a chain which runs parallel to c' sin B' with a
crankshaft motif. Equivalent chains are further
linked above and below to form a highly complex
polyhedral framework. The Fe(l)-O octahedron
shares three of its edges; one with Fe(l), namely
OWI-OW, and two with Fe(3)'s,namely O(l)-O(3)tt
and O(2)'-O(5)'. This immediate neighborhoodis the
3.(2)-cluster of Moore (l97aa). The Fe(3)-O octahedron shares two edges with Fe(l) octahedra.
Considering only the octahedra,this is the 2r(2) configuration of Moore (1974a).The Fe(2)-O distorted
tetragonal pyramids share a mutual edge O(4)-O(4)'
whose center is the center of inversion. In addition,
an unanticipated feature, the edge O(6)-0(8) is
shared with the P(2)O4 tetrahedron. We feel it
necessaryand desirableto point out the edge-sharing
neighborhoods, for they have considerable implications in homonuclear electron transfer-absorption where the probability of transfer is increasedas
the distance between metal centers is decreased.
As yet, no theory predicts or explains a priori Ihe
existence of such an unusual structure. In many
respects,the structure is reminiscentof the complex
graftonite structure.Although sarcopsideis a limiting
hexagonal close-packedoxygen structure, the hightemperature dimorph graftonite bears no obvious
relationshipwith it. This unusual structure,as shown
by Calvo (1968), possessesthree non-equivalent
metal positions, two five-coordinatedand one sevencoordinated. Despite attempts at severalprojections,
no obvious relationship to Fer(HrO)[POn],could be
found. Unlike Fe3(HrO)[POn]r,
no edgesin graftonite
are shared between the PO. tetrahedra and the fivecoordinated polyhedra. It is possible that these unusual structurescan be rationalizedvia some spherepacking theory.
Bond Distances and Angles
Ftc. 2. Polyhedral diagram of the Fe-O arrangement between
t / q< x ' < l z , w h e r e a ' = a - c a n d c ' : a + c T h e c h a i n - l i k e
c h a r a c t e ri s s h o w n b y s t i p p l i n g S o l i d d i s k s d e n o t el i n k a g e so f c o r ners above and below this slab.
Polyhedralinteratomic distancesare listed in Table
4. The averagesfor the Fe2+-O octahedral and P-O
tetrahedral distancesare within the range reported
for numerous well-refinedstructures.The polyhedral
interatomic angles in Table 5 reveal rather severe distortions for the octahedra, ranging from
O ( l ) " - F e ( 3 ) - O ( 3 ) 7 6 . 9 " t o O ( 2 ) t - F e ( 1 ) - O ( 3 ) "I 1 6 . 8 " .
The Fe(2)-O polyhedron possessesfive vertices,
but its angular distortions are so severethat distinction between tetragonal pyramidal and trigonal
bipyramidal coordination is not possible.According
to the interatomic angle distribution for these two
kinds of polyhedra in Stephensonand Moore (1968),
the Fe(2)-O polyhedron resembles a trigonal
bipyramid with the angle O(4)-Fe(2)-O(8) 170.0'
(deviatingby l0' from the ideal 180" angle),but most
457
CRYSTAL STRUCTURE OF Fe'+" (H,O) [PO],
Tlst-s 4. PolyhedralInteratomicDistances
for Fer(H,O)[POn]rt
Fe (I)
re(1)
"
"
"
"'
-o (s)|.l
- 0 ( 3 )- *
-ol,\l
-o (l) r
- 0 ( ? )*
-owa
2.o70
2.092
2.101
2"L52
2.166
2.393
2.161
average
-o (3) **
ii
0 (r)
-o (7) tt
-o (6)
-o (4) r
-o (4) *
-o (8)
Fe (2)
tt
It
tt
I
average
1 . 98 7
2.036
2.Os2
2.086
2.243
2.08r
F e( 3 ) - o ( 6 ) r i
- O( r ) i *
"i l
- 0 ( 2 )i r r
'r
- o ( 8 )i * - O( 5 ) *
"
-o (3)
"
.u::u*"
2.083
2.135
2.140
2"I45
2 "206
2.zLl-
-o (I)
r ,.
3 . r43
3.3s3
3.47e
3.626
3 .04I
average
1.548
o ( 1 )- o ( 4 )
0 ( 2 )- o ( r + )
2" 7 0 3 * o ( 3 ) - o ( r + )
2 7|rq
o ( 1 )- o ( 3 )
2 . 93 5
o ( 2 )- o ( 3 )
2.947
0 ( 1 )- o ( 2 )
-P(2)
Fe(2)
-o (6)
-0 (6)
- o ( 8 ). l ,
o (4) ..
o (4) ;
o (4);
0 (4)
2.975
3.03I
3.084
-o i zi "
oiqi
or'J -o (3) i*
o(r){ -o(s)ij
o(2)- -o(3)"
aver:age
1. s42
1.543
1 . 54 q
t. 561
2.48s
2.sL7
2.s36
2.s38
2.s40
2. s43
2.153
- o ( B )*
o(6)
o(4);r -o(4)or7)** -or8l..
ollla
P(1)-o (r)
" -o (3)
" -0 (2)
" -0 (4)
&
*
2.703
P(r)
Fe (3)
Fe (2)
*
3"r00
3.r00
-o (7) t-
average
average
P (2)
P(2)-o(7)
" -o (5)
" -o(6)
,' -o (8)
I.s2e
r.530
I.555
r.556
3 "037
average
I.542
) a,
; " ;,;
0 ( 7 )r
*
o (7)
2.526
3.108
3.318
3.391
Hydrugen Bonds
ow ...
0l\l "..
average
o ( 6 )- o ( 8 )
o ( 5 )- o ( 7 )
o (6) -o (7)
o(s)-o(8)
0 ( 7 )- o ( 8 )
o ( s )- o ( 6 )
2.413f
2.496
2 .s32
2"s3s
2. sss
2"s7L
2.5I7
average
+ i = -x,
*
-9,
octahedtaf
-z; ii = 7/2+x,
shared edges.
= 7/2-x, 1/2+g'
z; iii
+ Fe (2 )-P (2 ) shared edge.
7/2-9,
of the remaining distancesmore closely resemblethe
tetragonal pyramid. The Fe(2)-O 2.08 A averagecan
be compared with the M(2)-O 2.14 and M(3)-O
2.05 A averagesreported by Calvo (1968)for the disTesI-r 5.
re (1)
o (r) ,. -o (3)aa
o(s); -owi
0(2)*
o(l)J
o (2);
*
o (2)
-o[{*
-ow
-o (s) t
-0w,.
ow -ow:
o r r ). . - o w a
oiri *t-olv
]l-o6s1'
o (3)
o ( r )t r - o ( s t)*i r
0 (2)
-o (3)
70
elr
79
"89
80
"89
85.I2
8 7. 3 2
87.62
90.32
106.15
111.02
rL6
"77
torted tetragonal pyramid and trigonal bipyramid
respectivelyin graftonite. However, his material contains considerableMn'+ which probably contribute
to the longer averagesthrough partial solutions.
Polyhedral Interatomic Angles for Fe'(H,O)[POJz
Fe(3)
Fe(2)
79"rro
79.14
-z appTied to coordinate
in fabLe 2.
( re (z)-re (2) | shated edge.
o (6) ,. -o (8)
0 (4) ;r -o (4)
o (7) i--o (8) r,.
o (4) - -o (7) **
0 (4) r -o (6)
o (4) i -o (6)
0 (4) i -o (8) -.-.
o (4)' -o (7)ii
**
0(6) -o(7)
0 (4) -o (8)
68.47'
78.8s
8 9. 4 0
oR
otl
I0r.57
101.75
101"92
119" 30
136"86
1 7 0. 0 0
o (3) -o (6)
P (I)
76 " 89 '
78.43
86.60
8 7. 8 2
88.40
e0 "Is
9 0. 2 8
el.u
91.15
e4.43
ee" 35
104"31
o (1) -o ('+)
o ( 2 )- o ( 4 )
o ( 3 )- o ( 4 )
o(1)-o(s)
0 ( 2 )- 0 ( 3 )
o (1) -o (2)
106. r+0.
108.29
1 0 9. 5 8
110.73
1r0.73
110.9 8
P(2)
o ( 6 )- o ( 8 )
o (s) -0 (7)
o ( 6 )- 0 ( 7 )
o (s) -o (8)
o (7) -o (8)
0 (s) -o (6)
10I.760
1 0 9. 3 8
I10.39
110.46
r 1 1 . 83
rr2.88
458
P. B. MOORE, AND T. ARAKI
Severecation-cation repulsion acrosssharededges
results in some very short distances;thus 0(6)-0(8),
the edge shared by Fe(2) and P(2), equals 2.41 A,
whereas O(4)-O(4)', which is shared by two Fe(2),
equals 2.63 A. Th.esedistancesare the shortest for
their polyhedra. Short distancesbetween octahedral
shared edges also occur, with the exception of
OW-OWI 3.104. This latter distance reflects the
l o n g F e ( l ) - O W ' 2 . 3 8A b o n d .
Hydrogen Bonds and Electrostatic Valence Balances
The OW moleculecan donate two hydrogen bonds
with the most likely acceptorbeing O(7), which coordinates to P(2) and Fe(2) only. Accepting { : +l/6
for the hydrogen bond strength as suggestedby Baur
(1970),a model can be found where O(7) acceptsone
strong and one weak hydrogen bond: OW . . . O(7)
232i\ and OW-O(7)' 3.43A with the angle
O(7)-OW-O(7)' l00.lo. Two strong hydrogen bonds
would result in a very nearly saturated O(7) anion,
since
Fe(2)-O(7) and P(2)-O(7) are the shortest distances
for their polyhedra,the presenceofone feeblebond is
more likely.
The remaining anions deviate only slightly from
saturation by cations and accordingly show no
systematicdeviations in their Me-O bond distances.
All oxide anions associatedwith Fe(l) are slightly unFe(l)
Fe(3)
r97
Fe(3)
bf c'sin
0'
r)
Fe(3)
Fe(3)
tetll
Fe(3)
F e( l )
Fee)
Fe(3)
97
Fe(
3)
Fe(l
L
Fe(3)
Fe(3)
Ftc. 3. The links betweenthe Fe atoms where edgesare shared.
This diagram follows from Figure 2. Arrows, pointing in the plane
and above or below, denote edge-links.
with AI = -0.08, addingfurther supdersaturated
port to the likely preferentialoxidationat the Fe(l)
below.
site discussed
A ProposedOxidation Sequence
for
Fe'z+g(HzO)[POo],
Moore (1971)has pointed out that only certain compositions in the homologous series
Fe2+r(HrO)o[POn],
are capableof continuousoxidation of the metalswithout destructionof the structure. The compositions
are limited by the condition
of maintenanceof local electrostaticneutralityof
cationsabout anionsduring oxidation.Permissible
bondedunitsincludeHrO-bridgedferrousions(asin
whereFe2+(OH2)rFe2+
edge-sharing
Fe2+octahedra)
can be continuouslyoxidizedto hydroxide-bridged
ferric ions-Fe3+(OH)rFe3+.
On the other hand,
lead
hydroxide-bridged
ferrousions,Fe2+(OH)2Fe2+,
to extremeoxygen undersaturation.
Analogously,
suchspecies
as Fe3+(OH)or Fe3+(OHr)Fe3+
alsolead
to local chargebalancedifficultiesand are,accordingly, not observed.
Of the homologousseries,only n :
3 is capableof continuousoxidationto a stableferric
end-membersince permissibleend-membercombinations are preserved.Thus, the series Fd*,
- Fe3+r(OHLIPOo],
(HrO)sIPO.], (phosphoferrite)
(kryzhanovskite)
is observedin Nature; the others
decomposeto yield essentiallyamorphous ferric
equivalentsafter progressiveand completeoxidation (Moore, l97 l). A more recentstudy on pure
syntheticphosphoferriteand its ferric equivalent
has established
beyonddoubt the existence
of both
ferrousand ferricend-member
compositions
belonging to the samestructuretype when the hydrogen
atom positionsare excluded(Moore, 1974b).
Since Fd+(OHr)rFe2+ions occur in Fe'z+r(HrO)
[POn]r,we propose that a bounded mixed valence compositioncan occur as a stable crystal.
The mid-pointof the OW-OW' edgesharedbetween
two Fe(1)atomsis an inversioncenter.This suggests
that an upperbound for a stableoxidizedequivalent
would be Fe2+rFe3+(OHXPO4],,
whereFe(l) is completelyoxidized.
If such an oxidativesequencedoesindeedexist,
then mixed-valence
transferand intensepleochroism
should occur with maximum absorptionalong the
Fe(l)3+-Fe(3)'z+direction. Unique Fe-Fe separations across the shared edges are Fe(l)-Fe(l)
3.25A, Fe(l)-Fe(3)3.11and3.20A,and Fe(2)-Fe(2)
3.20A. We providea skeletonof Fe-Fe'connections
and distancesacrosssharededgesin Figure 3. These
distancesare similar to those found betweenthe
CRYSTAL STRUCTURE OF Fez+s(H,O) [PO,],
sharededgein vivianite,suggesting
that mild oxidation of Fe'+s(HrO)[POn],
would result in intense
pleochroism,similar to that observedfor vivianite.
Acknowledgments
459
computed from numerical Hartree-Fock wave functions. lcta
C rystallogr. A24, 321-324.
Moonr, P. B. (1971)The Fe'+'(H'O)"(POJ, homologous series:
crystal-chemical relationships and oxidized equivalents. lz.
Mineral. 56. l-7.
(f912) Sarcopside: its atomic arrangement. Am. Mineral.
We thank Dr. Enrico Mattievich of Centro Brasiliero de
s7, 24-35.
PesquisasFisicaswho brought the compound to our attention (19'l4a) Structural hierarchies among minerals containing
and who provided excellentcrystals.Mr. Dennis H. Lund conoctahedrally coordinating oxygen lI. Systematic retrieval and
structed the crystal drawings. ProfessorWayne Dollase offered
classification of octahedral edge-sharing clusters: an
many suggestions
toward the manuscript'simprovement.
epistemological approach. Neues Jahrb. Mineral. Abh. 120,
This study was supportedby the NSF Grant GA-40543and
205-227
the SloanFoundationGrant-in-AidBR-1489awardedto P.B.M.; (1974b)Evidencefor a completemixed valencesolid soluand a MaterialsResearchgrant awardedto the Universityof Chition series in Fe'z*'(HrO) [PO.t (phosphoferrite)cago by the National ScienceFoundation.
(kryzhanovskite).
Nature,Phys.Sci. 251' 305.
g(OH)g[PO.],
Fe3+
N., nNo R. SnlNlvnslr (1970) Fourier
RruecuexonrN,
G.
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