American Mineralogist, Volume 65, pages 4gg_49g, Igg0

The crystal structure of althausite, Mg.(pOJ2(OH,O)(F,D)

CunIsrnN RoutvilNc

Kjemisk Institutt, (Jniyersitetet i Oslo, Blindern, Oslo 3, Norway

AND GUNNEN RAEOS

Instituttfor Geologi, (lniversitetet i Oslo, Blindern, Oslo 3, Norway

Abstract

The crystal structure of althausite was solved by direct methods and refined to a final Rvalue of 0'022 for l164 high-angle reflections (sin d/I > 0.45A-r) with 1> 2.5o.Thepositionof the hydrogen atom was found from a difference Fourier synthesis. The structure is ortho-rhombic Pnma with a : 8.258(2), b : 6.05aQ), c : 14.383(5)A. Magnesium atoms occur inboth five- and six-fold coordination, and the coordination polyhedia are highly distorted.The Mg octahedra form chains along D by edge-sharing. Hydroxyl anA fluoine occur in alargely ordered distribution among two diflerent structural siies and occupy alternating posi-tions along 'channels'parallel to D. Partial vacancy in the (OH,F) sites is dnfirmed, the pop-ulation factor for the F site being 8l percent. The crystal-chemical formula of althausite istherefore Mgo@Oo)r(OH,OXF,!) with Z: 4.

The cleavages in althausite, {00U perfect and {l0l} distinct, occur along planes crossingrelatively few bonds and leave the chains of Mg octahedra unbroken. Bond-strength calcu-lations for althausite and wagnerite are presented and the OH content in wagner-ite is dis-cussed.

Preliminary results of hydrothermal syntheses indicate the existence of a series from F-wagnerite to OH,F-wagnerite and from OH-althausite to OH,F-althausite. Infrared spectra offluorine-free althausite show a splitting of the O-H stretching frequency, proving ih"t t*odistinct hydroxyl positions are present.

Introduction agreement with the calculated value, (010) n (l l0) :60.14". The optical orientation must be changed ac_

The new magnesium-phosphate mineral althausite cordingly to X: c, y : b, Z : a, OAp (010), a-nd thewas described from serpentine-magnesite deposits in hardneis on {010} is 3vz in the c direction and 4 inModum, south Norway, by Raade and rysseland the a direction.(1975). Based on a wet-chemical analysis, the empiri- The type locality for althausite is the Tin-cal formula was given as MgrPoo(oHo.3?Fo.25 gelstadtjern quarry, Modum, and the original de-Oo,nlo,r), with vacancy in the (OH,F) sites because scription was based on material from this occurrence.of a presumed substitution of the type 2(oH,F)- r= The mineral has also been found in a similar deposito'z-tr' Althausite is orthorhombic with a : 8.258(2), farther to the north, the overntjern quarry. Here theb : 14.383(5), c : 6.054(2)A, V:719.0(7)A3, Z : 8. althausite has a reddish-brown color and occurs in aThe space group was given as Pnar, but from the ex- somewhat different mineral association (talc, magne-tinctions, another possible space group is Pnam site, brown apatite, partly enstatite). Howevei, awhich was omitted. Furthermore, the cleavage was more complete account of the mineral paragenesesstated to be perfect along [001] and distinct along and the distribution of phosphate mineials *org001) ' New investigations show that the correct the deposits is reserved fo, a separate paper.cleavages are {010} (perfect, pinacoidal) and {ll0} Amlcroprobeanalysisofthebverntjernalthausite(distinct, prismatic). A set of rough measurements of using Tingilstadtjern althausite as standard gave thethe angle between the face normals of the perfect and Ottowingiesult (data calculated as direct ratios afterthe distinct cleavage planes gave 60-63o, in good background correction; values for the Tingelstadtjernw03-Mx/80/0506-o488$02.00 488

ROMMING AND RAADE: ALTHAUSITE

Table l. Weight loss vs. H2O + CO2 content for althausite and two

apatrteslyzer (Table l). The internal consistency of the data

is excellent (HrO value for althausite from Raade

and Tysseland, 1975).In the original description of althausite, the choice

of axes was made according to the scheme c 1 a 1 b.

In the structural description which follows, b and c

are interchanged in order to have the space-group

symbol in the standard setting, Pnma. The two cleav-

ages thus become {001} and {l0l} in the trans-

formed axial system.

ExPerimental

The cleavage fragment used for the structure de-

termination came from the Tingelstadtjern quarry'

Modum; it had approximate dimensions 0.2 x 0.2 x

0.05 mm. The X-ray diffraction data were collected

on a Picker four-circle punched-card controlled dif-

fractometer using graphite crystal monochromated

MoKo radiation. A unique set of intensities was mea-

sured, using tltre 0/20 scan mode with a scan rate of

2omin-' (20). The scan range was from 0.9o below

20(a,) to 0.9o above 20(ar); background counts were

taken for 30 sec at each of the scan limits. Out of the

163l reflections with sind/tr < 0.84-', 1456 were re-

garded as observed, their intensity being larger than

2.5 times the estimated standard deviation. The vari-

ance of the intensity was taken as d(1) : G + (0.02

C")'where G is the total number of counts and C" is

the net count. Three standard reflections measured

for every 100 reflections of the data set showed no

systematic variations. The intensity data were cor-

rected for Lorenz and polarization effects and for ab-

sorption fu(MoKa) : 10.07 cm-'].

Structure determination

Intensity statistics gave convincing evidence of a

centric structure, indicating the space group Pnma

(after reorientation according to International Tables

for X-ray Crystallography) rathet than Pna2, zs re-

ported earlier (Raade and Tysseland' 1975).

The positions of all non-hydrogen atoms were

found by direct methods using the program assembly

MULTAN (Germain et al.,l97l) and refined by suc-

cessive Fourier syntheses and least-squares calcu-

lations. So far the fluorine and hydroxyl oxygen

atoms could not be differentiated because of the simi-

larity in scattering power. A di-fference Fourier syn-

thesis revealed the position of a hydrogen atom close

to one of these atoms, however, which could thus be

identified as the oxygen atom.The cornposition of althausite found from chem-

ical analysis indicates that the hydroxyl and fluorine

positions are partially occupied and in part replaced

Weight loss

from TGA

( r e I . u n i t s )

Wt? o f H2O ana l CO2;

ca lcu la ted re fa t i ve

un i ts in paren theses

n : o 1 . B 7 s

H2O + CO2 l-.4'72

H2O + CO2 1.2'72

Althausite

( O H , F ) - a p a t i t e

( 6 0 . 4 )

l 4 ' 7 . s )

( 4 r . 0 )

material, after subtraction of apatite impurity and re-calculation to 100 percent, are given in parentheses):MgO 50.5 (51.0) , P,O, 44.4 (45.1) , F 3.04 (2.99)weight percent. The iron content was determinedwith the probe using a fayalite standard: total iron asFeO is 0.40 and 0.80 weight percent in the Tin-gelstadtjern and Overntjern althausites respectively.The higher iron content of the Overntjern mineralshould be noted. Its brown color is due to micro-scopic inclusions of iron oxides/hydroxides.

The Overntjern occurrence has provided a fewspecimens with subhedral crystals of althausite im-bedded in magnesite or talc. The crystals are elon-gated along c and flattened on D. Some natural sec-tions f c show the forms {010} and I l0]. Onesubhedral crystal has the approximate size a:b:c :

2: I :3 cm and shows the form {010} and four distinctterminal faces at one end of the crystal. Two of thesefaces belong to the same form, identified as {131}.The two other faces do not belong to the same formand no simple indices could be attached to them.These must be regarded as vicinal faces, developedbecause of imperfect growth of the crystal, whichmay be ultimately due to defects in the crystal struc-tute, e.g. in this case partly empty (OH,F) sites (cl

Terpstra and Codd, 1961, p. 360-363).The defect structure of althausite is clearly sub-

stantiated by the present structure determination, butwe would still like to mention other evidence whichsupports the correctness of the original chemicalanalysis. Firstly, the new mineral holtedahlite,(Mg,Na),(PO4,CO3OH)(OH,F), also from the Tin-gelstadtjern occurrence, was analyzed with the elec-tron microprobe using althausite as standard, with

HrO and CO, being determined separately with aPerkin-Elmer 240 elemental, atalyzer. In this way aperfectly stoichiometric formula was obtained forholtedahlite (Raade and Mladeck, 1979). Secondly,the weight losses were obtained from TGA runs onalthausite and two associated apatites from Tin-gelstadtjern. The HrO and CO, contents of the apa-tites were also determined with the elemental ana-

6 1

46

490 ROMMING AND RAADE: ALTHAUSITE

Table 2. Atomic coordinates and thermal parameters for althausite

u23UI3u11 u33

Ms(1 ) 0 .13402 (5 )

w l2 l 0 . 34763 (71

Ms(3) 0.0771217t.

P { r ) 0 . 48845 (s )

P ( 2 1 0 . 2 2 4 5 6 ( 5 1

0 (1 r ) 0 .38234 (10 )

0 (12 ) 0 .60739 ( I s )

0 ( 1 3 ) 0 . 5 9 r 4 7 ( 1 6 )

0 (2r) 0. r1s83 (r0)

0(221 0.32077 (16)

0 ( 23 ) 0 .34092 ( r s )

F 0 .33s00 (15 )

0 0 .09124 (1s )

H 0 . I 54 (7 )

0 .00414 (7 )

0 . 2 5

0 . 2 5

0 . 2 5

0 . 25

0 .04123 ( t 5 )

0 . 2 5

0 . 2 5

0. 04268 ( 15)

0 . 2 5

0 . 2 5

0 . 2 5

0 . 2 5

0 . 2 5

0 .168s8 (3 )

0 .42143 | 4l

0. 5750s ( 4)

0 . 14583 (3 )

0 .84820 (3 )

0 .14137 (6 )

o .06273 (91

0 .23ss4 (8 )

0 .85335 (6 )

0 .7ss88 (8 )

0 . 93021 (9 )

0 .56627 (8 \

0 .0758s (8 )

o . 035 ( 4 )

0 .0004 ( r )

0 .002 r ( 2 )

-0 .0007 (2 )

-0. 0001 ( I )

0 . 0004 (1 )

0 .0006 (2 )

0 .0012 (3 )

-0 .0029 (3 )

-0 .0004 (2 )

0 . c03s (4 )

-0 .0028 (4 )

-0 .0015 (3 )

0 .0008 (3 )

0 .0009 (1 )

0 . 0

0 . 0

0 . 0

0 . 0-0 .0006 (3 )

0 . 0

0 .0015 (3 )

0 . 0

0 . 0

0 . 0

0 . 0

0 . 0

0 ,0067 (2 )

0 .00s4 (2 )

0 .0068 (2 )

0 .0037 (2 )

0 . 0 0 4 3 ( 2 )

0 .006 r ( 3 )

0 . 0 0 6 4 ( 4 )

0 .0102 (s)

0 .0068 (3 )

0 .0108 ( s )

0 .0068 (4 )

0 . 0 0 6 4 ( 7 )

0 . 0 0 5 0 ( 4 )

B=1 .6 ( 7 )

0 .0049 (2 )

0 . 0 0 6 6 ( 3 )

0 .0063 (2 )

0 .0041 (2 )

0 .004s (2 )

0 . 0 0 6 9 ( 3 )

0 . 0 u 2 ( s )

0 .0080 ( s )

0 .0071 (3 )

0 .0076 ( s )

0 .0187 (6 )

0 .0055 (7 )

0 .0082 (5 )

o .oo85 (2 ) 0 .0009 ( r )

0 . 0 I 1 1 ( 3 ) 0 . 0

0 . 0 0 7 5 ( 2 ) 0 . 0

0 . 0 0 4 8 ( 2 ) 0 . 0

0 . 0 0 5 s ( 2 ) 0 . 0

0 . 0 r 1 2 ( 3 ) - 0 . 0 0 1 3 ( 3 )

0 .0072 (41 0 .0

0 . 0 0 6 5 ( 4 ) 0 . 0

0 .0120 (3 ) - 0 .0015 (3 )

0 . 0 0 7 5 ( 4 ) 0 . 0

0 . 0 0 8 5 ( 4 ) 0 . 0

0 . 0 0 5 7 ( 7 ) 0 . 0

0 . 0 0 7 1 ( 4 ) 0 . 0

The values of x, y, z a-re given jn fractional coordinates, the anisotJopic tenperature factor is of the form q(2r2(url a*2h2ru22b*2k2*v33 c*212r2vr2.*b*hkt2ur3

"*.*hr*2u23 b*"*kl)1. ustir-tea shndard deviations in pa-rentfpses refer

to the last diqits.

by oxygen ions. The further refinement by full-ma-trix least-squares methods included positional pa-rameters, anisotropic thermal parameters (for allatoms except for the hydrogen atom which was re-fined isotropically), and occupancy factors for hy-droxyl and fluorine. Atomic scattering factors usedwere those of Doyle and Turner (1968) for P, Mg andO, of International Tables for X-ray Crystallography(1962) for F-, and ofStewart et al. (1965) for hydro-gen. In order to reduce systematic errors due tofaulty assessment of atomic charge in the atomicform factors, only diffraction data with sindltr >0.454-' were applied for the last stage of refinement,reducing the number of applied observations to 1164.

No significant shift occurred in the hydroxyl occu-pancy factor; it was consequently fixed at its normalvalue for a fully occupied site. The fluorine site pop-ulation factor converged to 8l(l) percent ofthe cor-responding value.

The refinements converged to a conventional Rfactor of 0.022 for the reflections employed in the re-finements (R : 0.025 for all observed reflections), R.: 0.031, and S : l2wAF/(m - n)],r, : 1.76. Theoverdetermination ratio was 16.2.

The quantity minimized in the least-squares calcu-lations was XwAP, where w is the inverse of the vari-ance of the observed structure factor. A descriptionof the computer programs applied is given by Groth(1e73).

A rigid-body analysis showed that the thermal mo-tion of the phosphate ions to a good approximationcould be interpreted in terms of translational and li-brational oscillation. The bond lengths used in thediscussion of these ions are those corrected for libra-tion.

A difference Fourier map had its largest electrondensity at (0.442,0.250, 0.560), 0.94A from the fluor-ine site. The integrated peak amounted to about l/4of an electron, and, although indicative of the re-placement of some OH- for the F- ion, it was not in-cluded as a partially occupied hydrogen atomic posi-tion in the refinement, even if the presence of such anatom is probably significant.

The final atomic positional and thermal parame-ters are listed in Table 2. Interatomic distances andbond angles are reported in Table 3; estimated stan-dard deviations are calculated from the variance-co-variance matrix and include uncertainties in cell di-mensions. Observed and calculated structure factorswith estimated standard deviations are on deposit atthe Business Office of the Mineralogical Society ofAmerica.'

I To obtain a copy of this table, order Document AM-g0-133from the Mineralogical Society of America, Business Office, 2000Florida Avenue, N.W., Washington, D. C. 20009. please remit$1.00 in advance for the microfiche.

ROMMING AND RAADE: ALTHAUSITE

Table 3. Interatomic distances (A) and angles (') for althausite (with estimated standard deviations in parentheses)

r\41( r) -0 (rL)

Ms(1) -o

F19 (1) -F

Mg( I ) -0 (21)

l,ls (1) -0 ( 22 )

r"q (r) -0 (13)

2 . 1 0 0 ( 1 )

2 . 0 3 1 ( r )

2 . r 4 s ( t )

2 . 1 0 7 ( 1 )

2 - O 2 2 ( r l

2 . 0 6 0 ( r )

83 .08 ( 4 )

85.26 (41

8 1 . 8 0 ( 4 )

176 .8e ( s )

99 .87 ( s )

er .7s (s )9 9 . s 9 ( s )

L 7 2 . 3 3 ( 6 1

1 r 9 . 9 7 ( 6 )

8 2 . 0 7 ( 3 )

r 0 0 . s 3 ( 3 )

116 .41 ( 3 )

94.9'7 (31

176 (s )

96 .29 (11

es (2)

96.26(5\

lag(2) -F

Mg(2) -0 (12)

Mg (2) -0 (21)

Mg (2) -0

Ms(3) -F

M g ( 3 ) - 0 ( u )

tr lg (3 ) -o (23)

Mg (3) -0 (12)

0 -ng(t)

0 - H

0 -l,tS(Z)

0 -0 (23)

F -rrs (1)

r -Mg(3)

F -Ms(2)

P ( 1 ) - 0 ( 1 1 )

P(1) -0 (12)

P( r ) -o (13)

P ( 2 ) - 0 ( 2 1 )

P(21 -0(22)

P ( 2 ) - 0 ( 2 3 )

I4g (I) -0 (IU -Mg (3)

!q (2) -0 (12) - l4s (3)

Mg(1) -0 (13) -wtg( t )

Ms(r) -0 (21) -Ms (2)

Mg (1)-0 (22) -rtg (U

M9 (3) -0 (23) -H

2.086121

1 . 9 e 7 ( 1 )

2 . 0 4 8 ( r )

2.0L2(I't

2 . 1 3 3 ( 1 )

2 . 0 3 4 ( 1 )

1 . 9 s 2 ( r )

r .998(21

2 . 0 3 r ( 1 )

0 . 7 8 ( 6 )

2 .0 I2 (L ' , )

2 .939(21

2 . 1 4 s ( 1 )

2 . 1 3 3 ( 1 )

2 .086(21

1. s40 ( r )

r . s47 (1 )

1 . s45 (1 )

1 . s46 ( 1 )

r . s47 (1 )

r . 5 2 2 ( r l

98 . 94 (4 )

103. 74 (6 )

92 .62(61

94.'70 (41

9 e . 2 2 ( 6 1

137 ( 1 )

0 -Mg(1) -0 (13)

F -Ms( I ) -o (21)

F - Iaq( I ) -0 (22)

F -Ms( I ) -0 (13)

0 (2 I ) - iq l ( r ) -0 (22)

0 (21) - I ' ! l (1 ) -0 (13)

0 (22) -Mg(1) -0 (13)

0 ( 1 2 ) - M g ( 2 ) - 0

0 (21) -I '19(2) -0 (21)

0 (21) -Mg(2) -0

0 (1 r ) - rE(3) -0 (23)

0 (11) -Ms(3) -0 (12)

0 (23) -1,1s(3) -0 (12)

0 -H -o (23)

o -o (231-P(21

H -0 (23) -P(2)

r4s (3) -F -Ms ( 2 )

0 (11) - l ' l s (1 ) -0

0(11) -Mg(1) -F

0 (u ) -Mg( r ) -0 (21)

0 (11) - l 'E (I) -0 (22)

0 (u ) -Mg( I ) -0 (13)

o -Ms( l ) - r

0 - w ( 1 ) - 0 ( 2 r )

0 -Mg (1) -0 (22)

F -Mg(2) -0 (12)

F -Ms(2) -0 (21)

F -Mg(2) -0

0 (12) -tr lg (2) -0 (2I)

F -Ms(3) -0 ( I I )

F - r \E(3) -0 (23)

F -Mg (3) -0 (12)

0 (11) -Mg(3) -0 (1 I )

IE(1) -0 -Ms(1)

Mg( I ) -0 -H

Ms( I ) -0 -Ms(2)

H -0 -Ms(2)

MS(1)-F -LIE(1)

Ms( I ) - r -Ms(3)

Ms(1)-F -P1q(21

0 ( r 1 ) - P ( 1 ) - 0 ( 1 2 )

0 ( 1 1 ) * P ( r ) - 0 ( 1 3 )

0 ( 1 2 ) - P ( 1 ) - 0 ( 1 3 )

o(2D-P(21 -o(22)

o ( 2 1 ) - P ( 2 ) - o ( 2 3 )

01221-P(21 -0(23\

I 'E (1)-0 (11) -P (1)

l4s (2) -0 (12) -P (U

l4s (1) -0 (13) -P (1)

Ms(1)-0 (2I l-P(2)

r 'E (1) -0 (22) -P (2)

r 'E (3 ) -0 (23) -P (2 )

88 .22(41

8 0 . 3 6 ( 4 )

160. s8 (4 )

9 0 . 9 7 ( 5 )

r02 .35 ( 5 )

9s . 5s ( 4 )

8 0 . 2 r ( 4 )

r '77 .33 (4 \

80 . s8 (s )

1 1 9 . 0 0 ( 3 )

e I . 7 5 ( s )

r 0 1 . 5 9 ( 3 )

8 2 . r s ( 3 )

r 7 4 . 3 8 ( 6 )' 7 9 . 4 2 ( 5 1

r 2 0 . 3 8 ( 6 )

9 4 . 3 9 ( 6 )

rL2(21

99.28 (5 )

133 (4 )

9 1 . 7 4 ( s )

9 4 . s 0 ( 4 )

I 3 2 . ' 7 8 ( 3 1

I09 .22(41

1r0 .36 (4 )

107.19 (7 )

10e .84 ( 4 )

109. 25 ( 4 )

1 0 9 . 9 4 ( 8 )

1 2 9 . 4 8 ( 5 )

L22.86(81

130 .7s ( 4 )

1 3 2 . 1 6 ( 6 )

1 2 8 . 8 9 ( 3 )

126.94(81

r . 5431.5501 . 549

I q 4 q

r . 551

0 ( r r ) -P (1 ) -0 (11 ) I 1 0 . 4 3 ( 7 )

o(21 ) -P (2 ) -o (2 r ) 108.70 (7 )

Iq (3) -0 (11) -P (r)

M9(3) -0 (12) -P( I )

Mg(2) -0 (21) -P (2 )

H -0 (23) -P(2)

12e .68 (s )133.39 (8)

r29.87 (61

es (r)

Description of the structure

A stereoscopic view ofthe structure is presented inFigure l; the numbering of the atoms may be seenfrom Figures 2,3, and 4.

There are three non-equivalent Mg2* ions of whichone is situated in a general eight-fold position

lMg(l)l and two are located on mirror planes tMg(2)and Mg(3)1. Two non-equivalent phosphate ionshave the phosphorus and two of the oxygen atoms on

ROMMING AND RAADE: ALTHAUSITE

Fig. l. Stereoscopic pair of the althausite structure. One unit cell is shown (b < a < c); some additional atoms outside the unit cell havebeen included in order to complete the Mg and P polyhedra. Phosphate groups and OH groups are indicated by fitled bonds. Fig. 2(together with Figs. 3 and 4) can be used as a legend for identifying the different atomic positions.

mirror planes and two equivalent oxygen atoms ingeneral positions. The hydroxyl and fluorine ions aresituated on mirror planes.

Mg(l) (in general position) is coordinated in a dis-torted octahedron to one fluorine, one hydroxyl, andfour phosphate oxygen atoms. The coordinations ofthe two other magnesium ions are distorted trigonalbipyramidal, Mg(2) with ligands F-, OH- and threephosphate oxygen atoms and Mg(3) with ligands F-and four phosphate oxygen atoms. The arrangemenrsare visualized in Figure 3, which also shows the wayin which the polyhedra are connected. Each Mg(l)octahedron shares edges with two other Mg(l) octa-hedra, one Mg(2) and one Me(3) trigonal bipyramid.The Mg(l) octahedra form straight chains parallel tothe b axis (cf. Fig.2). The Mg(2) polyhedron sharesedges with two Mg(l) octahedra and one Mg(3) trig-onal bipyramid; the Mg(3) polyhedron shares edgeswith two Me(l) octahedra and one Me(2) trigonal bi-pyramid.

The arrangements around the anions are visual-ized in Figure 4. The two phosphate groups formnearly ideal tetrahedra with O-P-O bond angles inthe range 107 .2-110.4o. Seven of the eight phosphateoxygen atoms are coordinated to two magnesiumions, the last oxygen atom O(23) being engaged in ahydrogen bond to a hydroxyl ion and an ionic bondto a Mg(3) ion. These arrangements are all close toplanar, as can be seen from the angle sums aroundthe oxygens, which vary between 354.1 and 360.0o.

The fluorine ion is coordinated to two Mg(l) ions,

one Mg(2), and one Mg(3) ion, the fluorine site beingclose to the center of the Mg(l)-Mg(l)'-Mg(2) tri-angle (Fig. 4c). The possible hydrogen position for ahydroxyl-substituted fluorine site (cf. Structure deter-mination) is completing a distorted trigonal bipy-ramidal arrangement with the Mg(3)-H direction asthe trigonal axis.

The hydroxyl ion, in addition to the hydrogenbond to a phosphate oxygen atom O(23), is coordi-nated to two Mg(l) ions and one Mg(2) ion in a tet-rahedral arrangement.

An important feature of the structure is that theOH- and F- anions occupy alternating positionsalong the b axis, such that a kind of 'double channel'is formed by two adjacent rows of OH-/F- (Fig. 2).Along b, the distances F-O and F-H are 3.093 and3.06A respectively, whereas across the channels thecorresponding distances (between F and OH situatedat the same height above the plane ac) are a littleshorter, 2.942 and 3.02A respectively.

Discussion

Relation to other structures

Althausite belongs to a group of minerals withgeneral formula llz(){On)Z, where M is a divalentmetal atom (Mg, Fe, Mn, Cu, Zn),X is P or As, andZ is mainly OH andlor F (cl Richmond, 1940). Fourdiferent types of crystal structures are known amongthese minerals. Tarbuttite, ZnrPOoOH, is triclinic,space group Pl, Z: 2 (Cocco et al., 1966\ and is

ROMMING AND MADE: ALTHAUSITE

Fig. 2. The crystal structure of althausite viewed down the D axis(origin for the labelled axes is at the upper left corner of the

bottom plane). The P-O and O-H bonds are filled and the F

atoms are shown as filled ellipsoids. The Mg(l) octahedra form

chains parallel to the D axis by edge-sharing, and the individual

octahedra are only sligbtly separated in this projection. Note the

two adjacent rows of alternating OH and F along the 6 axis, an

arrangement that results in a sort of 'double channel' in the

structure. This figure may serve as a legend to the stereoscopic

views of Fig. l.

isostructural with paradamite, ZnrAsOoOH. Triplite,(Mn,Fe)rPOoF, and the isostructural iron analoguezwieselite are monoclinic, space Eroup I2/a, Z : 8(Waldrop, 1969). The structure of these two mineralsis closely related to that of wagnerite, MgrPOnF(Coda et al . , 1967), t r ip loidi te/wolfei te,(Mn,Fe),POoOH (Waldrop, 1970), and sarkinite,Mn AsOoOH (Dal Negro et al., 1974), which form aseries of monoclinic isostructural minerals with space

Erolurp P2t/a anld Z : 16, i.e. with a doubling of the baxis in comparison with triplite,/zwieselite. Anotherstructure type is displayed by the orthorhombic min-erals libethenite, CuTPO.OH (Walitzi, 1963), ada-

mite, ZoAsO4OH (Hawthorne, 19'16; Hill, 1976),and eveite, MnrAsOoOH (Moore and Smyth, 1968)'which all have the space gtoup Pnnm with Z: 4. Tothis series also belongs olivenite, Cu'AsOoOH, spacegroup nt/n [with a as the unique axis and a :

90.0(l)"1 and Z : 4 (Toman, 1977), whose mono-clinic structure deviates only slightly from the ap-proximate orthorhombic structure determined pre-viously (Heritsch, 1938). Interestingly, the silicatemineral andalusite, AlrSiOoO, Pnnm, Z : 4 (Burn-ham and Buerger, 196l) is isostructural with the lastseries of arsenates and phosphates, as was pointedout by Strunz (1936).

The synthetic compounds CdrPOoF and CurPOoFwith space $oup C2/c (equivalent to I2/a) are iso-structural with triplite (Rea and Kostiner, 1974;1976). CorAsOnOH is isostructural with adamite(Riffel et al., 1975), whereas Sn,PO,OH with spacegrotp F2,/n and Z: 4 has a distinct structure unre-lated to the others (Jordan et al.,1976). Several anal-ogous compounds with chlorine instead of F/OHdisplay still other structural types, as could be ex-pected from the larger size of the Cl- ion. Another re-lated group of minerals has the general formulaAB(XO")Z, where A and B may be two divalentmetal atoms of different size (Be, Mn, Mg, Fe, Zn,Cu, Ba, Pb) or one monovalent and one trivalentmetal atom (Li, Na; Al, Fe). Included in this groupare also some vanadates. A number of distinct struc-ture types are known among these compounds.

The crystal structure of althausite is unique amongthe structures of these minerals and synthetic com-pounds. Wagnerite, MgrPOoF, which is chemicallyclose to althausite, also has Mg in both 5- and 6-coor-dination, but has a much more complicated struc-ture, and its eight structurally distinct Mg polyhedraare connected differently. Another mineral that ischemically close to althausite is holtedahlite,

hexagonal and must belong to yet another structuretype. A structure determination of this mineral is inprogress. The iron analogue of holtedahlite is satter-lyite, recently described by Mandarino et al. (1978).

Althausite has some formal structural features incommon with the minerals libethenite-olivenite-ada-mite-eveite-andalusite, in that they contain similarcation polyhedra with 5- and 6-coordination and thesame kind of edge-sharing octahedral chains. The al-thausite structure, with a cell volume about twicethat of the others, has two different Mg" and OH/Fsites, so that other aspects of the structures show noclose relationship.

RAMMING AND MADE: ALTHAUSITE

Fig. 3. The three different Mg coordination polyhedra in althausite with their nearcst surroundings; oRTEp drawings, showingellipsoids of thermal vibration. (a) The [Mg(I)O4(OH)F] distorted octahedra form chains parallel to D by edge-sharing, and are in turnconnected with Mgv(2) and Mgv(3) polyhedra, also through edge-sharing. (b) The [Mg(2)Or(OH)F] distorted trigonal bipyramid sharesedges with two Mgvr(l) polyhedra and one Mgv(3) polyhedron. (c) The [Mg(3)oaF] disto(ed trigonal bipyramid sharesidges with twoMgut(l) polyhedra and one Mgv(2) polyhedron.

c

Cleavage

The perfect pinacoidal cleavage along {001} andthe distinct prismatic cleavage along {l0l} in al-thausite are plausibly explained on the basis of struc-tural information. These cleavages occur alongplanes which cross relatively few bonds and areformed by breaking bonds between phosphategroups and Mg polyhedra (Figs. I andz). The chainsof [MgO"(OH)F] octahedra running parallel to the 6axis, and which apparently constitute a strong entityin the structure, are left intact.

Note that the two cleavages in andalusite, distinctalong {ll0} and indistinct along {100}, are com-parable to the cleavages in althausite, and leave theAlOu chains which run parallel to the c axis unbro-

ken (based on the setting c < a < b, space groupPnnm). However, for the isostructural minerals li-bethenite, olivenite, adamite, and eveite, quite differ-ent cleavage directions are quoted in the literature,namely indistinct {100} and {010} for libethenite, in-distinct {011} and {ll0} for olivenite, good {lOUand poor {010} for adamite, and fair {l0l} foreveite, all cleavages apparently given for the samesetting c < a < b (cf.e.g. Roberts et al., 1974\. ltshould be expected that the cleavages of a series ofisostructural minerals were comparable, of coursenot in quality, but at least in direction. Cleavages re-ported for olivenite, adamite, and eveite, involving abreaking of the octahedral chains running parallel tothe c axes, must therefore be regarded as question-able.

Fig' 4' ORTEP drawings, showing ellipsoids of thermal vibration. (a and b) The two non-equivalent POo tetrahedra in althausite andthe connections between their oxygen atoms and the neighboring Mg atoms. (c) The bonding arrangement of the F atom. In syntheticalthausite this site may also be occupied by hydroxyl, with the G-H pointing in the opposite direction to the G-Mg(3) bond. (d) Thebonding arrangements around the OH site.

B"'il

Mg3 ]fo -:...K.iblr ret

$"'i("cba

t*$ &"n'

ROMMING AND RAADE: ALTHAUSITE

Table 4. Bond-strength calculation for althausite (valence units)

495

M g ( l ) M s ( 2 ) M g ( 3 ) P ( t ) P ( 2 )

0 ( l r )

0 ( 1 2 )

0 ( r 3 )

o ( 2 1 )

o (22 )

0 ( 2 3 )

0 . 3 3 0 0 . 3 7 9

0 . 4 0 9

0 . 0 4 2

x 2 +

x 2 +x 2 +

0 . 4 1 0

0 . 0 6 3

0 . 0 4 5

0 . 3 6 8 x 2 +

1 . 2 4 9 x 2 +

1 . 2 2 5

1 . 2 3 2

. l . 9 5 8 x 2 +

2 . 1 ? 8

2 . 0 5 8

2 . 0 0 3 x 2 +

2 . 1 0 1

0 . 1 0 1 . 9 4 8

0 . 9 0 2 . 0 5 9

0 . 9 8 0

0 . 3 5 9 x 2 +

0 . 3 2 60 . 0 4 30 . 0 3 7

0 . 3 8 8 x 2 +

1 . 2 2 9 x 2 +

1 . 2 2 5

I . 3 1 4

0 . 0 5 20 . 0 4 8

0 . 4 5 2

0

F

x 2 +0 . 0 4 1

x 2 +

0 . 3 8 ] x 2 + 0 . 3 9 7

0 . 2 3 6 x 2 + 0 . 2 6 6 0 . 2 4 2

2 . 1 0 0 x 2 + ' l . 9 9 9

2 . 0 4 5 4 . 9 5 5 4 . 9 9 7 1 . 0 0 , l 9 . ' l 9 6

C o m p u t e d f r o m t h e

B r o w n ( 1 9 7 6 ) a n d

e m p i r i c a l b o n d - s t r e n g t h

B r o w n ( 1 9 7 7 ) ,

b o n d - l e n g t h r e l a t i o n s o f B r o w n a n d } j u ( . l 9 7 6 ) ,

Bondlengths and bond angles .The mean P-O bond length (corrected for libra-

tion) is 1.548A with a standard deviation from themean of 0.003A; the average is taken over seven ofthe P-O bonds. The P(2)-O(23) bond is significantlyshorter, 1.5264, indicating a smaller negative netcharge on this oxygen atom. The reason is clearly in-dicated by the coordination ofthe phosphate oxygenatoms. O(23) is coordinated to one Mg(3) ion and isalso engaged as acceptor in a hydrogen bond (Fig.4b), whereas all the other phosphate oxygen atomsare each coordinated to two Mg ions.

The O-H bond length (0.784) is shorter than theaccepted O-H bond, which is 0.95A or longer if thehydrogen is engaged in hydrogen bonding. This isbecause the X-ray method measures the position ofelectron density maxima rather than the position ofthe atomic nuclei.

The distortion of the cation polyhedra conforms tothe generally accepted rule for ionic structures, thatshared edges tend to be shorter than unshared ones.This may be verified by inspection of bond angleswith magnesium ions as the central atom as given inTable 3.

B ond- s trength calculations

A bond-strength table for althausite is presented inTable 4, and is based on an 'ideal' structure withfully occupied OH- and F- sites. The P-O bondlengths utilized in the calculation are those uncor-rected for libration, since the empirical curves relat-ing bond strengths and bond lengths are based ondistances uncorrected for thermal motion (Brownand Shannon, 1973). As can be seen from the table,the bond-strength sums for althausite are satisfac-tory, with a maximum deviation of 6.4 percent forO(12). However, to achieve this it was necessary alsoto consider the contributions from the second-closestneighbors at distances (Me-O) from 3.09 to 3.494,although the calculated bond strengths may not bevery accurate for such long bonds. The large degreeof distortion of the coordination polyhedra in al-thausite makes the necessity of such an approachquite reasonable.

We have also calculated the bond sums for wagne-rite (Table 5). The sums for Mg are systematicallytoo low, and also in this case it might be necessary totake into account the contributions from oxygenatoms farther away. Similarly, highly distorted Mg

RAMMING ,4ND RAADE: ALTHAUSITE

polyhedra occur in the wagnerite structure as in thealthausite structure. Note the significantly low sumsaround two of the F- ions, F(2) and F(3). Wagneritesmay contain substantial amounts of OH- (see below),and possibly this hydroxyl is preferably substitutedin two of the four F- sites, so as to produce a partlyordered structure with regard to OH-/F-. However,further discussion of the bond-strength sums for wag-nerite is better postponed until a refined structure hasbeen determined for a wagnerite with known F:OHratio. We hope to undertake such an investigation ata later date.

Distribution of OH- and F

The OH- and F- anions have approximately thesame size and are frequently found to replace eachother completely. A well-known example among thephosphates is the pair fluorapatite-hydroxyapatite.However, in some instances the OH and F analoguesmay have different space groups and cell dimensionsand show a limited degree of solid solution, althoughthe structures are commonly closely related. Ex-amples, again taken from the phosphate group ofminerals, are the pairs zwiesel i te/ tr ip l i te,(Fe,Mn)rPOoF, and wolfei te/ tr ip loidi te,(Fe,Mn)rPOnOH, mentioned above. The main differ-ence between these structures is that F- occurs com-pletely disordered between two possible sites in trip-lite, whereas OH- is ordered in triploidite, probablyowing to the dipolar character of the OH- (Waldrop,1970). The site splitting in natural triplite may becaused by the presence of large amounts of thesmal ler Mg2* ion, s ince the pure compoundMnrPOoF does not show this disorder (Rea and Kos-tiner, 1972).

Apart from the similarity in size between OH- andF-, these anions have otherwise very di,fferent prop-erties with regard to polarizability and electroneg-ativity. Replacement and ordering of OH- and F-in crystal structures are thus generally controlled bythe coordination and kind of ligands of the structuralsites. On this basis, the high degree of ordering be-tween OH- and F- is readily explained in the case ofalthausite, where the two available sites have quitedifferent environments and one of them is preferredby OH-, the other by F- (Fig. 4, c and d). In wagne-rite also, some ordering of OH- and F- is indicated(see preceding subchapter). These anions may be, toa large extent, ordered in many other structures, butin most cases this is difficult to detect by X-ray dif-fraction methods. However, a OH-/F- anion order-

Table 5. Calculated bond-strength sums (p) for wagnerite

A t o n p ( v . u . ) A p ( v . u . ) AA t o n

I t s ' ( t )

M s " ( 3 )

M e ' ( 5 )

r 4 s ' ( 7 )

M s u t ( 2 )

t u t s u t ( 4 )

u g u t ( o )

l l s u t ( s )

P ( l )

P ( 2 )

P ( 3 )

P ( 4 )

F ( t )

F ( 2 )

F ( 3 )

F ( 4 )

1 . 9 4

t . 9 t

l 8 1

1 . 8 2

1 . 9 7

l 9 5

1 . 8 6

t . B 5

5 0 0

5 . 0 1

5 . 0 8

4 . 9 7

0 . 9 5

0 . 8 6

0 . 8 6

0 . 9 5

3 . 0

4 . 5

9 5

9 . 0

1 . 5

2 5

7 . 0

7 . 5

0 . 0

4 . 2

1 . 6

0 . 6

5 . 0

1 4 . 0

r 4 . 0

5 . 0

0 ( l )

0 ( 2 )

0 ( 3 )

0 ( 4 )

0 ( s )

0 ( 6 )

0 ( 7 )

0 ( 8 )

0 ( e )

0 ( 1 0 )

0 ( l r )

o ( r 2 )

0 ( r 3 )

0 ( r 4 )

o ( r 5 )

0 ( r 6 )

2 . 0 0 0 . 0

1 . 9 3 3 . 5' I

9 9 0 . 5' l . 9 3

3 . 5

I . 9 6 2 . 0

2 . 0 0 0 0

1 . 9 9 0 . 5

1 . 9 6 2 . C

1 . 9 7 ] 5

1 . 9 7 l 5

1 . 9 9 0 . 5

2 . 0 2 I . 0

2 . 0 6 3 . 0

L 8 6 7 . 0

2 . 0 1 0 . 5

I . 9 4 3 0

C o n p u t e d f r o m t h e e n p i r i c a l b o n d - s t r e n g t h - b o n d - l e n g t h

r e l a t i o n s o f B r o w n a n d | / J u ( 1 9 7 6 ) a n d B r o w n ( 1 9 7 7 ) , E a s e d

o n t h e s t r u c t u r e d e t e r m i n a t i o n o f C o d a e t a l . ( 1 9 6 7 ) .

P e r c e r t a g e d i f f e r e n c e b e t w e e n v a l e n c e a n d p .

ing has been found in the apatite structure by meansof neutron diffraction (Nozik, 1978).

The availability of F, the temperature and pressureof formation, and also the oxygen fugacity of the en-vironment are factors that control the degree of re-placement of F- and OH- in minerals. As discussedbelow, a completely F-free althausite has been syn-thesized, and this shows that F is not an essentialconstituent of the althausite structure.

The defect structure of althausite

Chemical evidence presented in the Introductionand the results of the structure determination haveconfirmed the original assumption made by Raadeand Tysseland (1975) that althausite has a defectstructure with partly empty (OH,F) sites. The struc-tural data show that the OH- occurs mainly in one oftwo distinct sites which has a full occupancy, and theF- ions and empty positions are confined to the othersite [population factor 8l(l) percent]. The position ofthe O'?- ions has not been proven, but considering theempirical coefficients obtained from the cherricalanalysis, (OHorrForroo,nEo,n), it is reasonable to as-sume that both OH- and O'- occupy the positionthat was found to be fully populated. The structural-

ROMMING AND RAADE: ALTHAUSITE

chemical formula for althausite should thus be ex-pressed as Mg(POo),(OH,OXF,tr), with possiblysome OH in the F site.

The occurrence of OH- and F- in 'double chan-nels' along b may be a clue to the existence and for-mation of a defect althausite structure, in that thesechannels may allow water to escape from the mineral(perhaps caused by a strong thermal event whichmay have affected these polymetamorphic serpen-tine-magnesite deposits), and further that the chan-nels may provide a possibility for adjustments ofatomic positions to compensate for the electrostaticimbalances brought about by the O'- ions and emptypositions. An analogy of great importance is pro-vided by the apatite structure, which also contains'channels' (along c) filled with OH-/F-/CI- andwhich has also been described with partially as wellas completely empty halide sites (e.9. McConnell,1973 for a review).

Synthetic work

Some preliminary results of hydrothermal syn-theses performed by G. Raade at Mineralogisches In-stitut der Universitiit Karlsruhe are presented here,since they have some bearing on the discussion of thealthausite structure.

At present, results from runs made at the followingpressures and temperatures are available: I kbar(650'C), 2kbar (550, 650'C), 4 kbar (400, 500, 550,600, 650'C), and'7 kbar (600'C). From mixtures ofMgHPO.'3H,O, MgF,, and Mg(OH), with the ratioMg:P:F :2: l :1 , only wagner i te has been obta inedas a pure phase with just a trace of OH as shown byinfrared spectroscopy. From a similar mixture withOH:F : l: l, a pure wagnerite phase is obtained insome cases, and mixtures of wagnerite and varyingamounts of althausite in others. The formation of al-thausite is clearly favored by higher temperatures/lower pressures compared to wagnerite, which is con-sistent with the denser packing of the wagneritestructure (Table 3 in Raade and Mladeck, 1979).This wagnerite contains considerable amounts of OHand has a somewhat larger cell volume than thenearly pure F-wagnerite. Also the althausite is a OH/F-bearing variety.

More interesting in the present context are the runsmade with F-free reactants, l.e. with Mg:P:OH :

2:l: l .In these cases mixtures of varying amounts ofOH-althausite and holtedahlite are produced, to-gether with several unknown phases. This althausitehas a somewhat larger cell volume than the OH/Fvariety.

Further experiments to elucidate the phase rela-tionships in the system MgrPOoF-MgrPOoOH arebeing undertaken. The preliminary results indicatethat there exist two series: from F-wagnerite to OH/F-wagnerite, and from OH-althausite to OH/F-al-thausite, but the limits of the substitutions have notyet been determined. Holtedahlite has only been ob-tained as a F-free phase.

The partially ordered site distributions of OH- andF- in natural althausite and possibly also in wagne-rite were discussed above. In synthetic OH-althaus-ite, the OH ions must occur in two different struc-tural positions. This is clearly corroborated by theinfrared spectroscopic study.

Infrared spectroscopy

The O-H stretching frequency of natural althaus-ite occurs at 3510 cm-' (Raade and Tysseland,1975).Using the Lippincott-Schroeder curve for the theo-retical relation between O-H frequency shift and hy-drogen bond length (Lippincott and Schroeder,1955), this gives an O-H "' O distance of ca.2.944in althausite, in good agreement with the value2.939 (2) A obtained from the structure determination.

Synthetic OH-althausite formed at 4 kbar and600"C shows a distinct splitting of the O-H stretch-ing band, with sharp peaks at 3510 and 3530 cm-'.The latter frequency corresponds to a slightly largerO-H ... O distance of ca. 2.97 A according to the Lip-pincott-Schroeder relation. This must imply an ad-justment of distances compared to the structure ofnatural althausite, where F-O(21) is 2.87A and F-O(H) is 2.94L.If OH were substituted for F- in thealthausite structure with the oxygen occupying ex-actly the same position as fluorine, a bifurcated hy-drogen bonding to the two nearest oxygens O(21)and O(H) would be the most likely result (Fig. 3c).This means that the O atom is both a donor and anacceptor of a hydrogen bond. However, an adjust-ment of distances could result in one of the bifur-cated bonds being preferred. As an ultimate corollaryof these changes, it is even possible that the spacegroup could be different for the OH-althausite, e.g.7fthe symmetry center is lost.

Natural wagnerite is often assumed to representthe pure F end-member, and HrO is rarely reportedin the analyses. However, wagnerite from Bambleshows important amounts of OH, according to the in-frared spectrum (cl Raade and Tysseland, 1975),and wagnerite from Sweden has a ratio F: OH :

l:0.81 (Henriques, 1956). The substitution of OH-for F- has a substantial influence on the refractive in-

498 ROMMING AND RAADE: ALTHAUSITE

dices, which are increased, and this is why the pointsfor the Swedish wagnerite fall offthe lines on the dia-gram presented by Propach (1976) to relate values ofrefractive indices and Fe,Mn contents for wagnerites.The O-H stretching frequency for natural as well assynthetic wagnerites occurs at 3570-3580 cm-', in-dicating an O-H ..' O bond distance of ca. 3.03A,which is similar to that of holtedahlite (Raade andMladeck, 1979).

AcknowledgmentsThe synthetic work from which some preliminary results are

presented here was made possible through a fellowship to G.Raade from the Alexander von Humboldt-Stiftung. The infraredspectra were recorded at Institut ftir Kristallographie, UniversitiitKarlsruhe. We thank W. Smykatz-Kloss of Mineralogisches Insti-tut, Universitet Karlsruhe for the TGA runs and C. J. Elliott atDepartment of Mineralogy, British Museum (Natural History) forthe H2O and CO2 determinations. W. L. Grimn at Mineralogisk-Geologisk Museum, University of Oslo gave assistance with themicroprobe analyses. A crystal of althausite was put at our dis-posal for measuremcnt by R. Hansen. We thank Professors E. Al-thaus and H. Wondratschek for their comm€nts on the rnanu-script.

ReferencesBrown, I. D. (1976) On the geometry of O-H...O hydrogen bonds.

Acta Crystallogr., A 3 2, 2+31.- (1977) Predicting bond lengths in inorganic crystals. Acta

Crystallogr., r-l-3, 1305-13 10.- and R. D. Shannon (1973) Empirical bond-strength-bond-

length curves for oxides. Acta Crystallogr., A29,266-282.- and K. K. Wu (1976) Empirical parameters for calculating

cation-oxygen bond valences. Acta Crystallogr., 832, 1957-1959.

Burnham, C. W. and M. J. Buerger (1961) Refinement of the crys-tal structure of andalusite. Z. Kristallogr., I I S, 269-290.

Cocco, G., L. Fanfani and P. F. Zanazzi (1966) The crystal struc-ture of tarbuttire, Zn2(OH)POo. Z. Kristallogr., 123,321-329.

Coda, A., G. Giuseppetti and C. Tadini (1967) The crystal struc-ture of wagnerite. Rend. Accad. Naz. Lincei, 43,212-224.

Dal Negro, A., G. Giusepperti and J. M. Martin Pozas (19?4) Thecrystal structure of sarkinite, Mn2AsOa(OH). Tschermaks Min-eral. Petrogr. Mitt., 21,246-260.

Doyle, P. A. and P. S. Turner (1968) Relativistic Hartree-Fock X-ray and electron scattering factors. Acta Crystallogr., A24,390-39'7.

Germain, G., P. Main and M. M. Woolfson (1971) The appli-cation ofphase relationships to complex structur€s. III. The op-timum use of phase relationships. Acta Crystallogr., A27,368-376.

Groth, P. (1973) Crystallographic computer programs for cynrn-74. Acta Chem. Scand.,27,1837.

Hawthorne, F. C. (1976) A refinement of the crystal structure ofadamite. Can. Mineral., 14, 143-148.

Henriques, A. (1956) An iron-rich wagnerite, formerly namedtalktriplite, from Hillsjriberget (Homsjdberget), Sweden. lrk.Mineral. Geol., 2, 149-153.

Heritsch, H. (1938) Die Struktur des Olivenites Cu2(OH)(AsO)o.Z. Kristallogr., 99, 466479.

Hill, R. f . 0976) The crystal structur€ and infrared properties ofadamite. Am. Mineral., 6 l, 979-986.

Jordan, T. H., L. W. Schroeder, B. Dickens and W. E. Brown(1976) Crystal structur€ ofstannous hydroxide phosphate, a re-action product of stannous fluoride and apatite. Inorg. Chem.,15, l8l0-1814.

Lippincott, E. R. and R. Schroeder (1955) One-dimensional modelofthe hydrogen bond. J. Chem. Phys.,23,1099-1106.

Mandarino, J. 4., B. D. Sturman and M. L Corlett (1978) Satter-lyite, a new hydroxyl-bearing ferrous phosphate frorn the BigFish River area, Yukon Territory. Can. Mineral., 16,4ll4l3.

McConnell, D. (1973) Apatite. Springer-Verlag, New York.Moore, P. B. and J. R. Smyth (1968) Crystal chemistry of the basic

manganese arsenates: III. The crystal structure of eveite,Mn2(OH)(AsOa\. Am. Minerat, JJ, 184l-1845.

Nozik, Yu. Z. (1978) Neutron diffraction mcthods for investiga-tion in the structure of minerals (abstr.). Phys. Chem. Minerals,J, 83-84.

Propach, G. (1976) Brechungsindizes und Dichten zum Bestim-men von Wagneriten (Mg,Fe)2POaF. Neues Jahrb. Mineral.Monatsh., 159-161.

Raade, G. and M. H. Mladeck (1979) Holtedahlite, a new magne-sium phosphate from Modum, Norway. Lithos, 12,283-287.

- and M. Tysseland (1975) Althausite, a new mineral fromModum, Norway. Lithos, 8,215-219.

Rea, J. R. and E. Kostiner (1972) The crystal structure of manga-nese fluorophosphate, Mn2(PO )F . Acta Crystallogr., 828,2525-2529.

- and - (1974) Cadmium fluorophosphate, Cdr(POa)F.Acta Crystallogr., 830, 2901-2903.

- and - (1976) The crystal structure of copper fluoro-phosphate, Cur(POa)F. Acta Crystallogr., 832, 1944-1947.

Richmond, W. E. (194()) Crystal chemistry of the phosphates, ar-senates and vanadates of the type A2XO4(Z). Am. Mineral., 25,4414?9.

Ritrel, H., F. Zettler and H. Hess (1975) Die Krisrallstruktur vonCo2(OH)AsOr. N eues Jahrb. M ineral. M onatsh., 5 l+5 17 .

Roberts, W. L., G. R. Rapp, Jr. and J. Weber (1974) Encyclopediaof Minerals. Van Nostrand Reinhold, New York.

Stewart, R. F., E. R. Davidson and W. T. Simpson (1965) Coher-ent X-ray scattering for the hydrogen atom in the hydrogenmolecule. J. Chem. Phys., 42, 3175-3187.

Strunz, H. (1936) Vergleichende rtintgenographische und mor-phologische Untersuchung von Andalusit (AlO)AlSiO4, Li-beth€nit (CuOH)CuPOa und Adamin (ZnOH)ZnAsOa. Z. Kris-tallogr., 94, 6{u--73.

Terpstra, P. and L. W. Codd (1961) Crystallometry. Longmans,London.

Toman, K. (1977) The symm€try and crystal structure of olivenite.Acta Crystallogr., 8 3 3, 2628-2631.

Waldrop, L. (1969) The crystal strucrure of tr ipl i te,(Mn,Fe)rFPOo. Z. Kristallogr., 130, l-14.

- (1970) The crystal structure oftriploidite and its relation tothe structures of other minerals of the triplite-triploidite group.Z. Kristallogr., I3l, l-20.

Walitzi, E. M. (1963) Strukturverfein€rung von LibethenitCur(OH)POo. Tschermaks Mineral. Pa ro gr. Mitt., 8, 614-624.

Manuscript received, October 18, 1979;acceptedfor publication, December 28, 1979.