Tun AUERTcAN MTxERALocIST
JOURNAL

Vol. 56

OF TIIE

MINERALOGICALSOCIETY OF AMERICAJANUARY-FEBRUARY

Nos. 1 and 2

THE Fe'z+3(HrO)"(POa)'
HOMOLOGOUS SERIES:CRYSTAL-CHEMICAL RELATIONSHIPS ANDOXIDIZED EQUIVALENTS
Paur BnraN Moono, Department of the Geo|kysical Sciences,
U nioersity of Ckicago, Chicago,I llinois 60637 .
AesrnA.cr
The atomic arrangements of the known Fd+3(IIrO)"(POo)z homologues are geometrically related and can be considered as progressive octahedral condensations from thehigher hydrates to the lower hydrates. Included in the series are vivianite (z:8), ludlamite(n:4), and phosphoferrite (z:3).
Kryzhanovskite is shown to be the oxidized equivalent of phosphoferrite. Its ceII
formula is approximately (Fe3+zsMn2+aeCaosMgo ,) ((OH)t 3(HrO)4teO,s,with a:9.404(16),b:9.973 (14), c:8.536 (14) A, spacegroup Pbna. Three-dimensionalcrystalstructure
analysis led to Ran:0.086 for 530 independent non-zero reflections. The kryzhanovskite(phosphoferrite) atomic arrangement consists of kinked edge-sharing octahedral chainsrunning parallel to the c-axis which link by corner-sharing to form sheets parallel to { tOO},
held together along the o-axis by the (PO)a- tetrahedra. The octahedrally coordinatedcations are strongly ordered, with essentially Fe3+ at the inversion center and mixed Fe3+,
Mn2+ at the general position. A proposed hydrogen-bonding scheme for phosphoferrite invoives open tetrahedral geometry.
Heating experiments on vivianite, ludlamite, and phosphoferrite show that only theferric equivalent of phosphoferrite yields single crystal data indicative of isotypy with theferrous compound. This phenomenon is explained by local electrostatic neutrality of the(OH)- Iigands in the kryzhanovskite structure which is not possible for the other ferric
equivalents. It is suggested that oxidation involves a temperature dependent auto-oxida.
tion-reduction mechanism within the crystal: 2Fe2+(HrQ)0+!l'eg+(OH)-*Hz'i

Iwrnooucrrorq
In a seriesof papers, I have explored the crystal chemistry of membersof the hydrated basic iron phosphates (Moore, 1965a, 1965b, 1970a,
1970b, 1970c).These recent investigations,based on three-dimensional
crystal sLructure analysesof key compounds,have brought to light structural interrelationships among many species in this extensive mineralgroup. Principal factors in their relationships are grounded on the different kinds of octahedral clusters which are stable in crystals. As suggested
by Moore (1970c), there appear to be only few predominant kinds ofclusters, the great number of speciesarising from Iigand stereoisomerism

P. B. MOORD
T.rsro 1. Cnvsrlr, Crr.rs or Fnz+s(H:O)"(POr)z-Fn3+e(OII)s(HrO),_a(POrr_
MN,+r(HzO)"(POr)z
Mnunnnso,Ab,A

9 239 (3s)9.e30(30)
8 . 4 s 3( 2 6 )9.404 (16) 9.462 (18) 9 489(26)9 973(r4) 10.O32(21) rO O74(27)8 s 3 6 ( 1 4 ) 8 . 6 5 9( 1 7 ) 8 . 6 0 1 ( 3 1 )

9.54
10 08
8.72

tr/,A'

7 7 s . s ( 2 . e ) 8 0 0 s ( 1 . 6 ) 8 2 1 . 9( . 2 . 1 ) 8 2 2 . s ( 2 . 9 )833 0Spacegroup

Pbna (possibly P2na)
4

z

10.08
13.43
4.7O
104030'616 0C2/m

1 0 . 5 4 1( 5 )4 646 (4)9 . 3 2 4( s )100026(1)/
449.1
P2la

1. Heated phosphoferrite (P-1,). This is the ferric equivalent of (3).
2. Kryzhanovskite (K-1). Using the analysis of Alekseev in Ginzburg (1950), the formula is (FeF+zzMn2+sr
Cao rMgo r, ((OII)z z(HrO)r.r) (POr)r o based on 8P
3 Phosphoferrite(P-1).UsinganalysisTinPalache,BermanandFrondel(1951),theformulais(Fep+sol4n2+rr
Cao a)(HrO)u r(POr)a o based on 8P.
4. "Landesite" (L-1). Using the analysis of Berman and Gonyer (1930), the iormula is (Mn2+aqFes+srMgr r
Mna+ooCao+)(OH, HrO)u r(?Or)a.o based 8P The reported amount of PuOrappears to be low.
5. Reddingite (R-5). Using analysis 5 in Palache, Bernan and Frondel, the lormula is (I\{a:+s eFe2+2.eFe3+or
Cao.r(HzO)u o(PO+)a-oThis is evidently the unoxidized equivalent of landesite. The cell parameters are
Irom Wolfe (1940).
6. Vivianite. The cell parameters are from Mori and Ito (1950).
7. Ludlamite. The cell parameters are lrom Abrahams and Bernstein (1966).

about some given cluster. Thus, the Iarge family of fibrous hydrated basic
ferrous-ferric phosphates is grounded on the octahedral face-sharing
trimer (Moore, 1970a),and many hydrated basic ferric phosphates (andsulfates) appear to be derivative of octahedral corner-sharing chains(Moore,1970c).
The present study is an attempt to show underlying structural principles within an homologous series, Fe2+3(H2O)"(POa)2,
where the quantity of water ligands, ?c,varies in a quantized fashion. Our subject includes three compounds-vivianite, n: 8 ; ludlami te, n : 4; and phosphoferrite, n:3. All three compoundsoccur principally as hydrothermallyrew'orkedproducts of triphylite giant crystals in granite pegmatites andin each speciesthe phosphate ligands are tetradentate and all watermoleculesare bonded as ligands to the Fe2+cations.In this paper, I shall
explore the topological and geometrical relationships among thesecompounds.
Of further interest is the observation that all three compounds mav
undergo partial to total oxidation of iron, extending our interest to theseries Fe2+a(HrO)"(POn)'-Fe3+'(OH)a(HrO)"j(PODz.
This study openswith a detailed account of the kryzhanovskitecrystal structure, a species
which representsthe oxidized equivalent of phosphoferrite.
KnyzuexovsKrrE: Irs Cnvsrar SrnucrunB
Introd.uction Kryzhanovskite was first describedand named by Ginzburg(1950). It is a rare specieswhose sole reported locality is the Kalbinsk

HYDRATED IRON PHOSPHATES

pegmatite in the U. S. S.R., where it occurswith sickleritein association
with a highly altered triphylite nodule. Ginzburg proposed the formula
the poor quality of the crystals, described
14nr+ps*+r(PO4)r(OH)r.H2O;
as monoclinic, prohibited goniometric measurement and establishmentof the crystal class.
Through the kindnessof Prof. A. S. Povarennykh, I obtained cleavage
fragments from a specimenin the Museum of the Academy of Sciences,
U.S.S.R.The fragments are deep red-brown in color and display glistening rust-yellow parting surfaces which, under microscopic examination,possessa crinkled, appearance.Several fragments proved suitable forsingle crystal X-ray study which established the relationship of kryzhanovskitewith phosphoferrite.This proved most fortunate, since theopportunity was available for the study of the phosphoferrite oxidized
equivalent. Accordingly, it was decided to perform a three-dimensional
crystal structure analysis on kryzhanovskite.
Although a preliminary account of the phosphoferrite crystal structure
was published by Flachsbart (1963),perusal of that paper revealedthat
aspects of the study were only partially correct. Evidently no further
details of that study appearedin print and I concluded that the phosphoferrite structure remained essentiallyunknown.
Erperimental. one fragment proved particularly suitable for single crystal X-ray study.
It was broken into several smaller pieces, some of which were ground with Si standard(o: 5.4301 A) and rolled into a 0.2 mm sphere using rubber cement. The calibrated powder
data utilized a 114.6 mm diameter Buerger-type camera and Mn-filtered Fe (K": 1.93728
A) radiation. The refined cell parameters, obtained initially from the single crystal study,
appear in Table 1 and the indexed powder data are ofiered in Table 2. The powder lines
were indexed on the basis of the intensities observed in the single crystal study. Considerjuxtaposedable difficulty was encountered in indexing, as many prominent reflections wereaxes
due to the dimensional similarity among the crystal ceil
The single crystal was a platelet exhibiting [001 ] parting, which measured 0.26X0.16
X0.10 mm. Preliminary examination includecl rotation and weissenberg photography.
2r[00 reflections were collected on a PAILRED automated difiractometer, using Mo-radiation and a graphite monochromator, a 2.60 half-angle scan with 20 second background measurements on either side of the maxima, and maximum 20:7O". These data include the 0
to 10 levels with c as the rotation axis. The data included the symmetry related pairs

the polar (001) reflections showed that the intensity maxima and minima did not exceed
8 percent of the mean value.
The final F(o6s) data included 550 independent "non-zero" reflections which wereabove the background average and 591 "zero" reflections including the systematic spacegroup absences.OnIy the "rror'-zeto" data were used in the ensuing analysis'

P. B. MOORE
Tawn 2. KnyzrlNovsr<rrr poworn Dara
(Fe/Mn rod.iati.on,
114.6mm canteratliameter,silicon stanilard.)
I /Iod(abs)

4

5.249
4.996
4.701
4.253
3.887

7
5
5
A

2
10
3
2
A

I
4
A

J .+JJ

3 156

3.O7r
3 .006
2.940
2.723
2.623
2.534
2.484
2.4ffi2.323
2.2A7d,(cal.c)

hkt

I /Io

d(obs)d(catrc)

hkl,

s.339

Irr

4.986
4.702
4.253
3.914
3.42t
3.175
3.065
3.013
2.942
2 7r4
2.627
2 526
2.47t
2.390
2 319
2.210

020
200
2to
121
220
22r
122
2t2
131
230
113
132
o23
123
141
41r

4
2
2

2.138
2.A84
2.058

2.153
2.W8
2.037
2.0rr
1.837
1.806
r.737
| 696
1.615
1.s66
1.550
I.497
1.483
r.M7

042
142
1r4
332
501
511
314
512
025
352
513
451
315
361

s

r.997

2
2
2
3
3
2
2
5
2
3
I
1
1

1.842
r.807
r.727
1.691
1.613
1.560
t.552
1503
1.481
1.453
t.437
1.270
1.132

Solufion of the Strueh$e. Both the film and PAILRED data exhibited systematicabsencesof the kind hh|, h+2n; h\l, hltr+2n; and 0k1.,hl2n. carefiir search failed
to revear any
violations of these systematic absences.Thus, the space group pbna is uniquelydetermined.
This result is not in agreement with Flachsbarcs (1963) structure analysisof phosphoferrite, which was based on P2na. Although caution must be expressed io
assu-irrg phosphoferrites actually crystallize in space grotp pbna, the conclusion of Fiachsbart
that the"9h3nse in the space grotp fuo.' Pbna to p2na (my orientation) is caused by the positionsof the POr tetrahedra and the HzO molecules,' appears untenable as
we shali see in subsequent discussion.
Solution of the kryzhanovskite structure proved straightforward and was initiated fromthe centrosymmetric average of the coordinate pairs for the Fe and p atoms
determined by
Flachsbart. Refinement of the coordinates for two Fe and one p in theas]"mmetric unit
led to Rr1,: g'29' Difierence synthesis revealed all the oxygen atoms remaining
in the asymmetric unit.
Ref'nement. Full matrix least-squares atomic coordinate and isotropic thermal
vibration
parameter refinement proceeded from a local moclification of the famlliar
ORFLS program
for the rBM 7094 computer, described by Busing, Martin, and Levy (1962).
Scattering
curves for Fez+,P3+,and o- were prepared from the tabres in Mac Gillavry andRieck (1962).
Twenty strong low-angle reflections showing substantiar secondary extinction
were excluded in the final stages of refinement and the remaining reflections were each given
unit
weights. Anomalous dispersion corrections were not applied since the only substa-ntial
contribution-f0
9 for the imaginary dispersion correction of iron-is trivial, comoared withthe uncertainties associated with the average scattering curves for theoctaherlral site
populations. Convergence r,l'asreached at

Rn*r:

l l r ( o a ' ) 1 -l n a a o l l: 0 086.
F(obs)HYDRATEDIRON PHOSPHATESCELI CoN:rnNrs, Arorurc Coonlrxerrs
Taer-r 3. KnvznaNovsrtrE
eul Isornoprc Teupnnetune Flcrots(Errors in parenthesesreJer to I'he last digits)

Fe(l)
Fe(2)
P8
o(1):oH
o(2)
o(3)
o(4)

4
8

o(s)

8

0(6):oH

8

4
8
8
8

r

y

z

B(L')

0.0000.4480(2).70e7(4)(16).4314.2r4r(ro). 1 1 1(41 1 ). 1s73(11). 3 s 8 (11 0 ). 4 7 0 (01 1 )0.0000- . 1 1 l s( 2 ).1032(4).2500
2ss2(1t)
(10)
.0336
(10)
.0839
.0446(10).338s(10)0.0000.1367(2).2106(4)
.0000
(rr)
.3273
.40e2(rr)0.61(4)86(3).42(s)
r.70(24).76(14). e s( 1 s ).rr+2(rr)
(rr)
.3027
. 3 6 3 (11 3 ).e0(1s).89(1s)r.2r (16)Further difierence synthesis of the three-dimensional data failed to reveal the hydrogen
positions, but these distances will be discussed on the basis of geometrical arguments.
3 and
The atomic coordinate and isotropic thermal vibration parameters are listed in Table-FGolc)
4r.
in
Table
appeardata
tn" lr'(oar) I

crystal chemistry and. interatomic d,istances.crystal cell contents
calculated from the cell volume in Table 1 and the specificgravity determination and the chemical analysis of O. A. Alekseev in Ginzburg (1950)

groups, the cell contents are approximately( F . ; : M " ; : c a o . s M e o . a )( ( o H ) z . a ( H : o )a . z()P o r ) s ,(kryzhanovskite) psr+3(H2O)a(POa),(phosphoferrite) -Fe3+3(OH)3(POn),(reddingite).
Mn2+3(HrO)a(POn)zr 1'o obtain a copy of Table 4, order NAPS Document 101219 from ASIS National AuxNew
iliary Publicatio.rs Service, c/o ccM Information Sciences, Inc.,22 W. 34th Street,yo.t, Ne* York 10001; remitting $2.00 for microfiche or $5.00 for photocopies payable to
ASIS-NAPS.

P. B. MOORE
Tesr,o 5. Krvzn.tNovsrrrB Cnvsral Cnrr, CoxrsNrs

-

12i^

1.50
1 63 9

CaO
MnO
FeO
Mgo
Fezo:
PzOr
HzO+
HrOinsol.

nt

130
34.62
3 5. 3 08.75
0.95
0 .5 6
99.37

0.441

<

2 6 7. 6

r./rl- frr.so
0.361

21.2
565.2

>M

t2.00

7 .08)

8.02

J/O.J

8.00

142.8

1597.6

1. Analysis of Alekseev in Ginzburg (1950).
2. Molecular weight in cell. computed from volume in Table 1
and specific gravity
determination of Ginzburg.
3 Cations in cell.
4. Ideal.

por,vnronet

Teer"E 6. Knyzrralovsrrrr(Esrimated stand.arderrors: MeO!0.01,
Fe(1)DtsreNcnsu
O_O,+0.02 A)

Fe(2)2 Fe(1)-Q(4;2 Fe(1)-O(6)
2 Fe(l)-O(s)Average:

1.964
2.or
2.r9
2.05-{

2 o(s)-o(6i)2 0(4)-0(6)
2 O(4)-O(6i)2 o(4)-o(si)

2 66b
2.73
2.88
2 e3

2 o(4)-o(s)2 O(s)-O(6)

2.e6
3.26

Average:

LrO

1 Fe(2)_O(z)I Fe(2)-O(1)
I Fe(2)_O(6)I Fe(2)-O(3)

2.ro
2 L3
2.14
2.1s

1 Fe(2) O(,;i)
1 Fe(2)_o(si)Average:

2.16
2.27
2 16

1 o(si)_o(6)2.66b1 o(3)_o(3i)1 O(1) O(3i)

2 6sb
2.8s

1 0(2)-0(6)2.e6
1 o(1)-O(3) 2.e6
1 O(3)-O(si) 2 99
1 O(1)-O(2) s 04
1 0(3)-0(6)
3 13
1 O(2)-O(si) 3 24
1 0(1)-0(6)s.24
1 O(2)-O(3i) 3.28
1 O(3)-O(s) 3 46.
Average: 304€ i :inversion operation
applied to coordinates in Table 3o Octahedral shired edges.

1 P_O(2)
1 P_O(s)1 p-O(3)
1 P-O(4)Average:

1 47
1 s2
1 s4
1.se
1.53

1 O(2)_O(3) 2 44
1 O(2)_O(s) 2 44
1 O(3)-O(s) 2.4s
1O(2)-O(4) 2SO
1 O(4)_O(s) 2 s1
1 O(3)_O(4) 2 60
Average: 2.50

HV DRATED IRON PHOSPHATES
Tarr,n 7. KnyznArovsrrre Er,rcrnosre:uc VALENCE
Bar,aNcnsAsour ANToNS(>)

o ( 1 ): 6 "Fe(2) fo(2)P * Fe(2)o(3)

P*Fe(2)*Fe(2)o(4)

P * Fe(l)o(s)

PfFe(1)*Fe(2)0(6) :6"

Fe(1) * Fe(2)

Fe(2)

2.5

_+_ 2.S

66
5 2.5
46
5 2.5 2.5
4- 6
6

-J+J 46

5 , 3 , 2.5
4-i6
3
2
.
5
-+66

0.83
r.67
2.08
1.75
2.r7
0.92

octahedral averages. It must be concluded from the cell contents andTable 6 that the octahedrally coordinated cations are considerablyordered, with predominant Fe3+ in the Fe(1) position with point symmetry 1 and mixed Fe3+ and Mn2+ at the general Fe(2) position, since
the averagesare Fe(1)-O 2.05 and Fe(2)-O 2.16 L respectively.Associated O-O' octahedral edgedistancesin Table 6 conform to simple electrostatic arguments since the octahedral shared edges are the shortest
distances for their polyhedra.
Likewise, the electrostatic valence balance calculations in Table 7
further explain the interatomic distances.From the cell contents and theaverageFe-O distances,the formal chargeon Fe(1) is ca. {3, and Fe(2)i s c a . ! 2 . 5 . I l e n c e , O ( 2 ) , w i t h > : t . 6 7 i s t h e m o s t u n d e r s a t u r a t e do f
the anions and affords the shortest MrO distances,i.e., Fe(2)-O(2)2.10 A and P-O(2) l.4t h, the latter an unusually short distance for
P5+-O. The most oversaturated anion, O(5) with E:2.17, possesses
considerably longer octahedral distances than average: Fe(1)-O(5)2.I9 A and Fe(2)-O(5) 2.27 A. For the anions which are nearly neutral,compensationoccurs,f or if P-O is long Fe-O is short and ai.ceaersa.Thesearguments, along with the observed isotropic thermal vibration parameters which indicate fully occupied anion positions, substantiate chargebalance through the substitution of hydroxyl groups for water moleculessince the substitution of 02- for HzO would leave voids in the structure.
Further ,discussionon the relative stabilities of the structures of theoxidized hydrated iron phosphatehomologuesappearsin the next section.

P. B. MOORE

Flachsbart's (1963) FrO interatomic distances for phosphoferrite,
which rangefrom 2.10 to 3.26 A, appea. to be in error. Unfortunately, no
mention is made of the data collection and further study on phosphoferrite will be necessary if accurate interatomic distances are to beobtained for that species.
GBNonar CnYsrar CunursrnY oF rHE
Houorocuns
Fe2+3(H2O)"(POn),
Topology. The atomic arrangements of the three homologues' vivianite,ludlamite, and phosphoferrite (kryzhanovskite) are known. Each structure may be conceived as a denser condensation of octahedral clusters of
its higher hydrates. The octahedral cluster formulae for the three species
can be written on the basis of M"4", where @are the vertices, s of which
are associatedwith ther M-octahedra. In vivianite M,Qu:Feadro, where
gr:phosphate oxygen and Oo:water oxygen.
dro:8 Op*8 On, withFor ludlamite M.Qu:Fesdrz,where.drz:8 Op*4 Os; and for phosphoferrite M,6": Feadu,where {11: 8 Op*3 On.
For all these structures, appropriate projections yield a striking relationship. This relationship can be seen in the polyhedral diagrams forvivianite, ludlamite, and kryzhanovskite (phosphoferrite) in Figures 1, 2,
and 3 respectively. The cell criteria for ludlamite and vivanite appear
in Table 1 for comparative purposes. Projections down the vivianite c*,the ludlamite Dx and the kryzhanovskite @*axes show similarity in theorientations of the octahedra and tetrahedra. Locally, these orientations
approximate fragmented hexagonal close-packedunits or strips, with theaxes of projection normal to the close-packedoxygen layers. These threecompounds are not truly close-packedsinceit is not possibletopologicallyto continuously deform the polyhedra into ideal closestpackings without
breaking and rearranging some bonds. Since the systems are not topologically close-packed,they will be called interrupted.close-packings.The
orientations of the interrupted close-packedlayers reflect similarities inthe translationsnormal to theselayeri: c sinB)ooo-6)7,6-af2)t,a-4.7 A,
which is the typical repeat distance for a hexagonal close-packedoxygen
framework.
Accordingly, the homologous series can be conceived as a progressive
condensation of octahedral clusters, from open clusters in the high hydrate to sheets in the lower hydrates. The vivianite structure, investigated by Mori and Ito (1950), consistsof insular octahedral edge-sharing
doublets and insular singlets joined to form slabs perpendicular to theD-axisby the (PO+)r tetrahedra (Fig. 1). In ludlamite, further fusion
occurs, with the appearance of octahedral edge-sharing linear triplets
corner-linked to similar triplets, forming somewhat open trellises oriented

HYDRATED IRON PHOSPHATES

Frcs. 1-3. Polyhedral diagrams of the vivianite,ludlamite and kryzhanovskite atomic arrangements.
Frc. 1. Vivianite projected down the z*-axis. The tetrahedra are stippled and connect to octahedral levels above and below. The coordinates are from Mori and Ito (1950).

parallel to {102f . The trellisesare linked to each other by the (POa)3tetrahedra oriented in a fashion similar to vivianite (Fig. 2). The ludlamite structure was first investigated by Ito and Mori (1951) andrefined with high accuracy by Abrahams and Bernstein (1966) aspart of a detailed neutron difiraction study. The kryzhanovskite (phosphoferrite) structure, Fig. 3, consists of infinite kinked edge-sharing
octahedral chains which link at free corners to form sheets oriented
parallel to {100}. These sheets are connected along the a-axis by thebridging (POo;t- tetrahedra which are oriented akin to vivianite andludlamite.
The geometrical relationships among members of this homologous
series are clearly evident. It was stated elsewhere(Moore, 1970b) thatthe controlling factor in the paragenesisof such compounds is the relative
stabrlity of water ligands with respect to temperature. With increasing
temperature, a series of "condensation" reactions take place, the stepwise loss of water resulting in the fusion of more open octahedral clusters
to form more condensed arrangements. Analogously, with decreasing
temperature the reversewould be truel as water ligands increasein quantity in the structures, more open arrangements appear. This accounts

10

P. B. MOORE

Frc. 2. Ludlamite projected down the y-axis. The octahedral edge-sharing triplets at
are ruled. The tetrahedra, which link to octahedral levels above and below are!:l/2
stippled. The coordinates are from Abrahams and Bernstein (1966).

for the fact that phosphoferrite is usually the earliest-formed member ofthe series,postdated by ludlamite which in turn is postdated by vivianite.
Such sequencescan be seen in specimenscollected from hydrothermallyreworked triphylite pods, such as at the Palermo f 1 mine, North Groton,
New Hampshire; Bull Moose pegmatite, Keystone, South Dakota; andHagendorf Siid, Bavaria.
It would be instructive to attempt synthesis of compounds in thishomologous series. So far, only vivianite, ludlamite, and phosphoferrite
appear to be the three known compounds. However, no detailed synthesis has ever been made, nor has any detailed study been undertakenon the myriads of hydrothermally reworked products of triphylite. It isquite likely that other members of the seriesstill remain to be discovered.
HvonocpN BoNuNc
Although there exist geometrical relationships among the vivianite,ludlamite, and kryzhanovskite (phosphoferrite) structures, there do notHYDRATED IRON PHOSPHATES

Frc. 3. Kryzhanovskite projected down the r-axis showing theoctahedral sheets and the connecting tetrahedra (stippled).

appear similar relationships in their hydrogen bonding schemes. It isonly possibleto offer a qualitative discussionsince the vivianite structure
is approximately known and since kryzhanovskite possessesmost of theoctahedral cations in the trivalent state. Abrahams and Bernstein (1966)
presented relatively accurate hydrogen positions for ludlamite which
they obtained from careful X-ray and neutron diffraction studies. Ludlamite remains the only structure where the hydrogen bonds are known,
quantitatively as well as qualitatively, with sufficient accuracy.
Figures 4, 5, and 6 show the probable hydrogen bonding schemesfor
the three species.Thesefigurescan be superlmposedupon the polyhedral
diagramsin Figure I,2, and 3. The O-H . . . O bond is representedas anarrow whose head points in the direction of the oxygen atom accepting
the hydrogen bond and whose tail is situated at the oxygen atom of thewater molecule. According to Abrahams and Bernstein, the O . . . O

P. B. MOOREor

I
Frcs. 4--6. Probable hydrogen bonds in ludlamite, vivianite and kryzhanovskite. These
diagrams can be superimposed on the Fig. 1 series. The tails of the arrows are centered on
the water oxygen and the heads point to the hydrogen acceptors.
Arrangement in ludlamite.

bo{Frc, 5. Arrangement inII YDRAT]J,D I RON PHOSPHAT ES

IJ

c
b{-

-1

L

J
l'ro. 6. Arrangement in kryzhanovskite.

distances in ludlamite are relatively short, ranging from 2.541 (3) to
2.750 (3) A. Three of the four (POa)r oxygen atoms are receptorsofhydrogen bonds, with one oxygen atom receiving two such bonds. The
resulting network in ludlamite (Fig. a) consistsof a rhombus-like outline
and insular bonds, both geometries of which are tilted away from the*z-plane. In this manner, the bonds link between populated octahedrallevels.
The geometry of the vivianite structure leads to a probable hydrogenbonding scheme which can be represented as a closed tetrahedron (Fig.
5), distinct from ludlamite in that all the receptors of the bonds are watermolecules.These bonds are situated between the octahedral levels andare the only chemical bonds which are broken by the perfect 1010f
cleavagein vivianite crystals. Geometrically, it does not appear possible
to select bonds which accept oxygen atoms associatedwith the (PO)3tetrahedra.
The probable hydrogen bonding scheme for kryzhanovskite, andpossibly phosphoferrite, in Figure 6 is based on an open tetrahedron.
Some of these bonds Iink between the octahedral levels. This scheme
involves two of thefour (POn;a- oxygen atoms, with O(4) accepting two
bonds. The shortest distance,2.57(2) A, is between O(2) . . . 0(6). The
remaining distances, 0(6) . . . O(4) 3.10 (2) and O(1) . . . O(4) 3.21
(2) A, are considerably longer than typical distances in inorganic salts

P. B. MOORE

involving water molecules. It must be stressed,however, that the oxidized nature of kryzhanovskite would lead to substantial disorder in the
O-H . . . O bonds, especially for O(1) and these distances may differ
substantially from those occurring in unoxidized phosphoferrite.
Of the three structures, only vivianite possesses
hydrogen bonds which
are necessarycomponents in the rigidity of the crystal structure sinceboth phosphoferrite and ludlamite involve three-dimensionallinkages of. . . M-O-P-O . . . bonds. As discussedin the next section, this difierence may contribute in part to the instability of vivianite crystals upon
progressiveoxidation of the iron.
Oxrperrox SreunncBs
Vivianite, ludlamite, and phosphoferrite are known to undergo rapidoxidation at low temperature in the presenceof air. Accordingly, crystalsof vivianite andludlamite from the Palermo f 1 mine, and phosphoferrite
from Hagendorf Siid were heated in air at l20oc, 180oC,and 240oC forfive days in open capillaries calibrated with a chromel alumel thermocouple in contact with the crystals. The products were then quenehed toroom temperature, dissolved in cold HCI solution, and titrated against
potassium dichromate solutions. Ludlamite at I2O"C and 180oC wasonly superfi.ciallyoxidized and yielded identical powder patterns as thestarting material. At 24OoC,the product proved to consist of iron in theferric state only, but the powder lines were diffuse and totally unrelated
to the starting material. Vivianite at all three temperatures was totally
oxidized to essentiallyamorphous material. On the other hand, phosphoferrite heated at 24OoCwas oxidized to its ferric equivalent and yieldedsuperior single crystal and powder photographs which indicated isotypy
with the ferrous material. The only difierence was considerableline andspot broadening in the oxidized materials.
Figure 7 presents available analyses and the results of the heating
experiments on the phosphoferrite-kryzhanovskite-reddingite series.
Unheated phosphoferriteis labelled P-1, its oxidized equivalent p-1,;
kryzhanovskite is labelled K-1. The available analyses of reddingite(Palache,Berman, and Frondel, 1951),labelled R-1 to R-5, are also included. Finally, "landesite", properly a ferrian reddingite according to
Moore (1964),is designatedL-1. Cell parametersfor P-1, P-1', K-1, and
L-t are given in Table 1; they are based on single crystal studies and therefined powder data using the indices obtained for kryzhanovskite. The
cell parameters for landesite reported by Moore (1964) are modified as aresult of more complete and corrected Miller indices derived from thekryzhanovskite three-dimensional single crystal data. The crystal cellvolumes are dependent on the relative states of oxidation, with the cell

HY DRATED I RON P HOSPHATESFe2*SPHOFERRITE
I

\

\

R-5
R-4
R-3
R-2
R-1
Mn

\

\

REDDINGITE KRYZHANOVSKITE
\

\

\
\

\

K-t P-l'Fe3+(Fea+)-redFrc. 7. Triangular diagram of the phosphoferrite (Fd+)-kryzhanovskite
dingite (Mn'+) end-members. Compositions are plotted as mol fractions of the end-members. R-1 to R-5 refer to reddingite analyses 1 to 5 in Palache, Berman and Frondel (1951),
L-1 is the composition of "landesite" (the oxidized equivalent of R-5), K-1 is kryzhanovskite, P-1 is phosphoferrite from Hagendorf Siid and P-f is its oxidized equivalent.

volume decreasing with increasing iron oxidation grade. The relationships among the cell volumes are consistent with the crystal radiiMn2+) Fe2+) Fe3+,which are the only major octahedrally coordinatedcations in Figure 7 and whose relative proportions in the crystal can beobtained from this figure. With the exception of powder line broadening
for the ferric members, thesecompounds appear to be crystallographically
isostructural.
Why should the oxidized equivalent of phosphoferrite exist as at'stable" crystal whereas the oxidized equivalents of vivianite and ludlamite are structurally unstable? The explanation appears to lie in thecriteria necessaryfor local electrostatic neutrality of the anions about
cations. In ludlamite, vivianite, and phosphoferrite, crystal structure
analysis has establishedthat all water moleculesare bonded as ligands tothe octahedrally coordinated iron atoms. In vivianite, the water molecules are each associated with one iron atom. Thus, the hypothetical
ferric end-member, written Fe3+a(OH)a(HrO)s(PO4)r,is unstable sincet6

P. B. MOORE

OH- are severely undersaturated electrostatically with respect to Fe3+.
No example is known of OH- only coordinated to a single Fe3+ cation.
Additional instability is probably induced through the breakdown ofhydrogen bonds which are essential for structural rigidity. Indeed,oxidized vivianites characteristically show a flaky appearanceparallel to{o1o}.
In ludlamite, each water molecule is associatedwith two iron atoms.
Writing the hypothetical oxidized equivalent as Fe3+3(OH)a(HsO)(PODz,
the HrO molecule remaining is severely oversaturated and consequently
the crystal is unstable. The oxidized equivalent of phosphoferrite, which't p.a+r(OH)a(POr)2,
is essentiallyneutral since each hydroxyl group isbonded to two Fe3+cations in octahedral coordination.
Analogous to vivianite, progressiveoxidation of Fe2+in phosphoferrite
should lead to dark green to blue color. Since phosphoferrite consists ofedge-sharing octahedral chains oriented parallel to the c-axis, homonuclear mixed-valence electron transfer would result in strong absorption
by the crystal parallel to {001}. Finally, the pure ferric equivalent, likethe ferrous compound, would appear relatively weakly pleochroic, incontrast with crystals possessingiron in mixed valence states.
What is the mechanism accounting for progressive oxidation of phosphoferrite? The most likely is one of auto-oxidation-reduction by cleavage of protons from the water ligands, forming hydroxyl groups andferric iron, that is, 2Fe2+(H2O)0+lps3+(QH)-*H, f . A test for the
existence of such a mechanism would involve heating phosphoferrite inanaerobic environments and quantitatively collecting hydrogen.
Regardingkryzhanovskite,it is reasonableto state that the compoundis formed by oxidation of parent phosphoferrite but it is uncertain
whether or not kryzhanovskite is thermodynamically stable since it has
not been synthesized directly from ferric salts. Evidently, the temperature of kryzhanovskite formation was too low for the oxidation of Mn2+:
it is generally observedthat Fe2+oxidizesbefore Mn2+ in mineral crystals
containing both cations in solid solution.
Acrxowt,rocrmNrs
The study of a natural oxidized equivalent of phosphoferrite was made possible throughthe generous contribution of type kryzhanovskite by Prof. A. S. Povarennykh. Prof. D. J.
Fisher supplied the phosphoferrite specimen from Hagendorf Std.
Financial assistance throughout this study was supplied by an Advanced Research
Projects Agency grant administered to the University of Chicago and the NSF GA10932
research grant.
RnnEnexcss
Anneruus, S. C., lNl J. L. Bnnrsrrrx(1966) Crystal structure of paramagnetic ludlamite,
FeB(PO4)r'4HrO at 2090K. J . C hern. P hys. 44, 2223-2229.

H YDRATED I RON PHOSPHATES

1aBrnuex, H., aNo F. A. GoNvrn (1930) Pegmatite minerals of Poland, Maine. Amer.
Minuol'. 15, 375 386.
Busrrc, W. R., K O. MearrN, eNo H. A. Lr.vv (1962) ORFLS, a Fortran crystallographic
least-squaresprogram.LI. S.Cl'earinghouseFeil.Sci.Tech. InJo. Rap' ORNL-TM-3OS.
Fl.ncnsennr, L (1963) Zur Kristallstruktur von Phosphoferrit, (Fe, Mn)3(POr)z'3HrO.
Z. Kristallogr. ll8, 327-331.
Iro, T., ANDH. MoRr (1951) The crystal structure of ludlamite. Acta Crystdlogr.4' 4124t6.
Mrc Grr-r,avnv, C. H., lNr G. D. Rrncr, eds. (1962) Internotional Tobl'es Jor X-ray
Crystallography, Vol. 3., The Kynoch Press, Birmingham, Engiand'Moonr, P. B. (1964) Investigations of landesite. Am.er. Minual" 49, 1122 1125.
(1965a) The crystal structure of laueite Amer. Mineral'.50, 1884-1892'(1965b) A structural classification of Fe-Mn orthophosphate hydrates. Amer.
Mineral, 50, 2052-2062.
(1970a)Crystal chemistry of the basic iron phosphates. Amer. LIineraL 55' 135-170.
(1970b) A crystal-chemical basis for short transition series orthophosphate andorthoarsenate parageneses N euesJ ahrb. M iner ol. M onatsh. 1970, 39-M.
-(1970c) Structural hierarchies among minerals containing octahedrally coordinating
oxygen. I Stereoisomerism among corner-sharing octahedral and tetrahedral chains.
N euesJ ahrb. M i.neral. M onatsh., 197O, 163-173.
Monr, H., ,c.xn T. Iro (1950) The crystal structures of vivianite and symplesite. ,4rr@
Crystal,logr.3, l-6.
Prucnr,C., H. Brnu.LN, lNo C. FnoNoBr. (1951) The System oJ Minerotrogy, Yol' 2' 7th
E d . , J o h n W i l e y & S o n s ,N e w Y o r k , 7 2 7 - 1 3 1 .
Wor-ln, C. W. (1940) Classifcation of minerals of the type A3(XO r)z'nHzO. Amu. Mineral.
25.738-753.
Manuscriptreceitd,

f une 16,1970; accepted'Jorpubli'cation,October 14, 1970.