AmericanMineralogisl, Volume62,pages 256-262, 1977

Minyulite:its atomicarrangement

ANrHoNy R. Keupr'l

Department of the Geophysical Sciences The Uniuersity of Chicago, Chicago, Illinois 60637

Abstract

Minyulite,K[Al,F(H,O),(PO,)rl, orthorhombic, space group pba2, a9.337(5), b 9.j40(5), c 5.522(3)A,Z : 2, possessesrigid dimericclusters of formula [AlrF(HrO)1(PO.)r(O")r], topologicallyidentical to the [Fe!+(OHXHTO).(SOn)r(O")r]clusters in copiapite,where Op and Os correspondto the phosphateand sulfate ligands,respectively. The structurewas solved by Pattersonand Fourier syntheses. atoms were located by difference synthesis.Least-squares refinement converged to R(hkl) = 0.022for 618reflections. The dimericcluster consists of two Al3+-O octahedrasharing one F- vertexand two POr tetrahedra, which further link the octahedra. The clusters link via shared octahe- dral-tetrahedralvertices to form sheetsparallel to {001}.Cavities in thesheets are occupied by K+ ions. One tetrahedralvertex is unsharedand acceptsfour hydrogenbonds from water moleculescoordinated to Ale+.These hydrogen bonds provide the only linkagebetween the sheets. The greateraffinity of Al8+ for F- than (OH) and the violation of electrostaticvalence balancewhen F- bonds to more than two Als+ cationsare suggestedas the reasonsfor the condensationof Al8+ octahedrainto dimers and chainsin aqueoussolution, leading ulti- matelyto the crystallizationof minyuliteand fluellite.The leucophosphitestructure may be preferredin the absenceof F-.

Introduction Al3+-Fee+,phosphates, including leucophosphite, Minyulitewas originally described by Simpsonand KFeg+(OH)(PO4)r.2HrO,and its Al3+ analog.They LeMesurier(1933) as a new speciesfrom Minyulo noted that minyulite and leucophosphitecan be Well, WesternAustralia, where it occursas radiating synthesizedby the treatmentof clayswith phosphate groups of fine fibers on the surfacesof crevicesin anions at pH rangesappropriate for soil environ- phosphaticirqnstone. Using optical methods,they mentsand at temperaturesless than 95oC.They pro- establishedorthorhombic symmetry and proposed posed that theseminerals may be important in the the formula KAlr(OH,F)(POn)r.3.5HrO.Spencer e/ fixationof inorganicphosphate anions in soils. al. (1943)studied minyulite from Wait's quarry near Leucophosphitebears a striking chemical sim- Noarlunga,South Australia, where it occursin phos- ilarity to minyulite,and besidestheir possibleforma- phate rock as short prismaticcrystals in sub-parallel tion undersimilar conditions in the soil,the report of growth coatingapatite. From X-ray oscillationpho- leucophosphitein phosphaticrock associatedwith tographs,they determinedthe cell constantsa 9.35, iron ore at Bomi Hill and Bambuta,Liberia, by Ax- b 9.74,c 5.52Aand the spacegroup PmmL, the hemi- elrod el al. (1952) is further indication of similar morphic nature of the crystalsbeing establishedby paragenesesfor thesetwo minerals.A comparisonof etchfigures. The formulaKAlr(PO1)r(OH,F).4H2O, the structuresof minyulite and leucophosphitemay Z :2 wassuggested. lead to an understandingof the conditionsnecessary Hasemanet al. (1950) synthesizedminyulite, as for their formation. well as a number of other hydrous K+-NH1+, Also of interest for structural comparisonis the mineralfluellite, AlrFr(OHXHTO)s(POo). 4HrO. Mur- I (1973) fluellite Presentaddress: Geology-Mineralogy Section, Los Angeles ray reported occurring associated County Museumof Natural History, 900 ExpositionBlvd., Los with minyulite in phosphaterock near Wolffdene, Angeles,California 90007. Queensland,Australia, and fluellitehas been verified 256 KAMPF: MINYULITE 257

on a specimenof phosphaterock from Moculta Tesrr 2. Minyulite.Atomic coordinate parameters Quarry,Angaston, South Australia, provided by J. E. Johnsonof the SouthAustralian Museum. Atom Mult. Experimental The crystalstudied was extractedfrom a specimen K 2 0.0000 0.0000 0.0000 A1 A 0.3s91(l) o.1r0s(1) 0.ss4s (4) from Wait's Quarry,kindly providedby J. E. John- son. Some difficulty was encounteredin finding a P i 0.1470(1) 0.3243(r) 0.2040(4) suitable single crystal, owing to the sub-parallel 0(r) A 0.4832(2) 0.178s(5) 0.1798(s) 1 (s) 0.46s8(3) o.i382(6) growth of individuals.By splittingcrystal clusters, an o(2) 0 .207s 0(3) A 0.207s(3) 0.2168(2) 0.0310(6) acceptablecrystal fragment was obtained, measuring 0 (4) 0.18s0(2) 0.2918(3) 0.467s(6) 0.07mm alongthe a andb axes,and 0.10 mm along the c axis.The crystalwas mountedparallel to the c 0w(r) A 0.2383(3) 0.042s(3) 0.67s3(7) (2) A 0.428s(3) 0.2s11(3) 0.7202(7) axls. 0Il/

Precessionphotographs indicated systematic ab- f 2 0.0000 0.5000 0.8217(6) sencescorresponding to the spacegroups Pbam and A (8) Pba2.The intensities (maximum H(l) 0 .226(4) 0.i10(4) 0 . ss6 of l3l5 reflections H(2) A 0 .234(4) 0.486(s) 0. s97(s) 20 : 55") weregathered on a Pickerautomated dif- H(5) A 0.3s2(4) 0.263(4) 0.606(8) fractometer utilizing graphite-monochromatizedH(4) A 0.002(4) 0.281(4) 0.608(8) MoKa radiation.Very smallmosaic spread permitted narrow half-anglescans of 0.4' with a scanrate of 1.0'/minute. Twenty-secondbackground counting times were used on either side of each reflection. determinedthe spacegroup to be Pba2.Subsequent Least-squaresrefinement of 30 referencereflections Fourier synthesisresolved the positions of all the yieldedthe cell constantsgiven in Table l. remainingnon-hydrogen atoms. Systematicabsences indicated by the intensitydata The atomic coordinatesand thermal vibration pa- confirmedthe spacegroup Pbamor Pba2.The data rameterswere refinedusing the NUCLS program, a wereprocessed by conventionalcomputational pro- modified versionof ORFLS by Businget al. (1962). parameter ceduresto obtainlF(obs)1. No absorptioncorrection Three cycles of full-matrix atomic and wasapplied, owing to the favorablesize and shapeof isotropic thermal vibration parameter refinement the crystaland the small absorptioncoefficient (p = convergedto R(hkl) : 0.044.Two cyclesof refine- ll.0 cm-1). After eliminationof the extinctreflec- ment usinganisotropic thermal vibration parameters tions and averagingof the symmetryequivalent re- convergedto R(hkl) : 0.033.A differenceFourier flections,618 independentreflections remained for synthesisyielded the locations of four unique H the ensuingstudy. atoms. A final two cyclesof refinement,including hydrogenatoms and applyinga secondaryextinction Solutionand refinementof the structure correction,converged to R : 0.022(Rw : 0.024). Three-dimensionalPatterson synthesi s, P(uuw),re- The extinctionparameter converged to 4.0(2)X l0-6. vealedthe positionsof the K, Al, and P atomsand Initially an atom was assignedto the atomic position (0 k 0.82). This yieldeda negative Test-e l. Minyulite.Crystal cell parameters temperaturefactor. During the final cyclesof refine- ment,fluorine was assigned to this location,and the parameters arEt e.337(s) final thermal vibration werecomparable 6iti 9. 740 (s) to thoseof the other anions.A fluorinedetermination (ii s.s22(3) " by Spenceret al. (1943)yielded 2.7 weightpercent F, Space group Pba2 indicatingat leasttwo fluorineatoms per unit cell. Z 2 Atomic scatteringfactors for K", Alo, Po,Oo, and

Forrnula KAl2F (H2O) z(POq) z Fo wereobtained from Cromerand Mann (1968) and includedthe anomalousdispersion terms for K, Al, Specific gravityl 2.46 Density (calc) grn/crn3 P, and O. Scatteringfactors for H were obtained from et al. (1965).Final atomiccoordinates rspencer Stewarl. et al. (1943J. are presentedin Table 2 and anisotropicthermal 258 KAMPF: MINYULITE

Tlsls 3. Minyulite.Anisotropic thermal vibration parameters*

Brr Bzz 8ae 9tz Br: Bzt

K 0.0031(r) 0.0049(r) 0.0r72(6) -0.0007(l) A1 0.0016(r) 0.0016(1) 0 . 00ss(4) 0.0001(1) -0.0003(2) -0.000i (2)

P 0.0016(1) 0.0016(r) 0. 0047(3) 0.0025(1) 0.0006(2) 0.0006 (2) o(1) 0. 0016(2) 0 .002e(2) 0. 0070(9) -0.0001(2) 0.0001(s) -0 .0006 (s) o(2) 0.0020(3) 0.0018(2) 0.0119(11) 0.0001(2) -0.000e(4) 0.0007(s) o(3) 0 . 0023(3) 0.0023(2) 0. 0089(1 0) 0.0007(2) 0. 0000(4) -0.0013(s) o(4) 0. 0028(3) 0.0037(3) 0.0070(9J 0.0003(2) -0.0004(s) 0.oo09 (s)

ohl(1) 0.003s(3) 0.0029(3) 0.0071(10) 0.0006(2) 0. 0000(s) -0.0010(s) oI^I(2) 0.0030(3) 0.002e (3) 0.007e(e) 0 . 0003(2) 0.0005(s) 0.000s(s)

F 0 .0024(4) 0 .0024(3) 0 . 0060(1 r) -0.00cs(3)

The anisotropic temperature factors are defined as coefficients in exp[-(Brrh2 + Bzzk2 +9339.' + 2g12hk + 28rsh.0 + 2S23k1) I .

parametersin Table3. The structurefactors are listed beenreported by Fanfan\et al. (1973)in the structure in Table4.' of copiapite.In this mineral,Fe8+06 octahedra are joined via a common OH vertex and are further Descriptionof the structure linked via two SOr tetrahedrato form a rigid poly- hedralcluster topologically equivalent to that in min- Topologyand geometry of the structure yulite.Although the ligandenvironment of Me3+in Minyulitepossesses AIO'F octahedrawhich share the two structuresis identical,the linkage between F verticesforming [Al,F(HrO)4(Op).]octahedral di- clustersis not related.In copiapite,the clustersare mers,where Op correspondsto oxygensdonated by linked into chainsby sharingvertices of non-cluster the phosphateligands. Two (POr) tetrahedrafurther (SOn)tetrahedra (see Fig. 3 of Fanfaniet al.). link the octahedraof eachdimer, resultingin a rigid polyhedralcluster with ideal point symmetrymm2 Interatomicdistances andthe formula[AlrF(HrO)n(PO.)dop)r]. Each clus- Interatomic distancesand hydrogenbond angles ter sharestwo octahedraland two tetrahedralvertices are givenin Table 5. No abnormalaverage distances with tetrahedraand octahedraof four adjacentclus- arenoted, and no distinctionbetween Al-F and Al-O ters, thereby forming sheetsoriented parallel to the distancesis obvious.The electrostaticbond strength {001}plane. K+ cationsoccupy pockets in the sheets sumsabout the anionsare tabulatedin Table 6. The surroundedby four linked clusters.Significant devia- bimodaldistribution of Al-O bond distancesis con- tion from the ideal 4mm symmetryof the sheetsis sistentwith the extendedelectrostatic valence rule of probably necessaryto provide a stablecoordination Baur (1970).Al forms long bonds to two for the K+ cation. Figure I depictsthe minyulite which are each oversaturatedwith respectto their sheetdown the z axis. Hydrogenbonds between the bond strengthsby 0.29e.s.u. and short bonds to three water moleculesof the octahedraand the unshared oxygenswhich areundersaturated by 0.13,0.13, and verticesof tetrahedrain adjacentsheets represent the 0.25e.s.u. only interlayerbonding, accountingfor the perfect The distanceH(l)-H(3) is l,9l(5)A, significantly {001} observed in minyulite. shorterthan the minimum allowabledistance of 2.0A Me3+ octahedralcorner-sharing dimers have not suggestedby Baur (1972)between of dif- been previouslyreported in any phosphatemineral ferentdonor groups.This leavessome doubt con- species.However, a similar polyhedral cluster has cerningthe accuracyof the hydrogenatom locations. Hydrogen bonding '? To obtaina copyof Table4, orderDocument AM-77-039 from Onephosphate oxygen, O(4), in minyulitedoes not the Businessoffice, MineralogicalSociety of America, 1909 K Street,N.W., Washington,D C. 20006.Please remit $1.00in ad- directlybond to any other cation.Instead, it achieves vancefor the microfiche. approximate electrostaticneutrality by accepting KAMPF: MINYULITE 259

four hydrogenbonds from water moleculesligated to rangementwas also noted by Baur and Khan (1970) the aluminum.Nonlinking phosphateoxygens have in the crystalstructure of Nar(HrO){POsOH). alsobeen reported in the mineralsmetavauxite (Baur and Rama Rao, 1968)and seamanite(Moore and Relationto leucophosphite Ghose, l97l). The oxygenreceives three hydrogen Moore (1972)showed leucophosphite to possessa bondsin metavauxiteand four in seamanite.The four structurebased on a discreteFe3+ tetramer, idealized hydrogen atoms which hydrogen bond to O(4) in in Figure I of that publication.The aluminumanalog minyulitehave been located in Figure 1. It can be of leucophosphite,prepared by Haseman et al. seenthat the four hydrogensand the Pu+cation de- (1950),bears a strikingchemical similarity to min- fine a tetragonalpyramid about O(4): Such an ar- yulite;yet, while both structuresare based on discrete

\ \ \ \\ t... \

..\ib- -"

\\ ,\ lowtrtl

Flc. l. Polyhedraldiagramoftheminyulitestructuredown[001].TheAl-OoctahedraarestippledandtheP-Otetrahedraareruled. K-O bonds are shown as dashed lines and OW-H bonds as dotted lines. 260 KAMPF: MINYULITE

TlsI-e 5. Minyulite. Interatomicdistances

H-bonding

A0 - 0(3) .s04 (3)fr P - o(3) 1.s26(3) ol4l(1) -H (2) 0.76(4) - o(1) .826(3) - o(4) I .s31 (4) 0l4l(1)-H(1) 0.81(4) - o(2) .844(3) - 0(2) r .s34 (3) ol4|(2) -H (3) 0.e6 (4) F .8sr(2) - o(1) ol^J(2)-H(4) 0.e8 (4) -0w(2) .s92(4) average average 0.88 -0h'(1) .004(4) average .887 - o(r) o(3) 2.469 (4) (4) -H(3) r.76(4) (4) o o(r)- 0(4) 2.48r -H(4) 1.88(4) 0(2)- 0(4) 2.4ss (4) -H(1) -ol^'(1) 1.9s(4) o(3) 2. ss3 (s) o(2)- 0(3) 2.4s7(4) -H(2) 2.08(4) F-oI4'(2) 2.se6 (3) o(3)- o(4) 2. s28(S) F-ov\'(1) 2.601(5) o(r) - o(2) 2.s3s (4) average 1 0? F- 0(2) 2 .63r (4) average 2.501 0(2)- 0(3) 2.637(4) F- o(1) 2.640(4) 0!v(2)-H(3) -o(4) 2.72 o(1)-ol\'(2) 2 .682(s) 0w(1)-H(1) -0(4) 2.76 o(2)-0I\'(r) 2.6e1(sl 0l{(1)-H(2)-0(4) 2.84 o (3)-ol^' (2) 2.704(4) 2K-O(2) z. d55 tJ..l or\I(2)-H(4) -o(4) 2.86 2.7 os (4) 2K-0(3) 2.870(3) 0W(1)-ol^l(2) average 2,80 0(l)- o(3) 2.7 28 (4) 2 K -ow(t) 2.87 4 (3) 0(1)- o(2) 2.744 (4) z K -ow(2) 2 .9s2(3) 0I4I(2)-0 (4) 2.697(4') Z.OOJ 2 average aveTage .888 ol{I(1)-o(4) 2.737(4) 0l4I(2)-o(4) 2.804(4) 0l4I(1)-o(4) 2 .804(4)

average z.toL

Mes+ clusters,the clustersare topologically unre- ous solutionwhich commonlycondense by sharing lated.Haseman et al. synthesizedeach of thesephases (OH)- ligands.Under the solutionconditions noted from low-temperatureaqueous solution. The details for the preparationof leucophosphite,the stableclus- of their synthesesappear in Table7. The formationof ter in solutionis apparentlythe tetramer.The stabili- thesephases can probablybe tracedto the formation zationof the minyulite dimer in solutionscontaining of the particularMe8+ cluster in solution.In light of F- is probablythe resultof a somewhatgreater affin- the indicationby the structureanalysis that the bridg- ity of Al3+for F- thanfor (OH)- andthe inability of ing ligandin the minyulitedimer is predominantlyF-, the tetramerto accommodateF- as its bridging li- it is particularlynoteworthy that F- was necessary gandswithout severelyviolating electrostatic valence only in the preparationof minyulite. The implication balance. is that the bridgingligand controlsthe natureof the The strong affinity of Al3+ for F- is well known. clusterand, thereby, the phasewhich will crystallize. The octahedralfluoride complexesof aluminum are Fe3+and Al3+ form octahedralcomplexes in aque- remarkablystable in aqueoussolution. All sixspecies from [Al(HrO)uF]'*to [AlF.]3- are formed.In min- TlsLr 6. Minyulite. Electrostatic valence balances of cations eralogical systems,fluoride is often selectivelyin- about anions corporatedin phasescontaining octahedrally-coordi- nated Al3+. The fluoroaluminates,which crystallize from fluoride-rich aqueoussolutions, possess struc- K+ A03+ H+ xpo tures basedon isolated[AlF6]3- complexes or on 0(1) 3/6 linkagesof these complexes.Numerous minerals s/4 l.7s 'formed o(2) L/8 s/6 s/4 in lessfluoride-rich environments incorporate o(3) r/8 3/6 s/4 !.17_ 0 (4) s/4 4x7/6 i.3t F- at sitescoordinated to two Al3+cations. The requirement of electrostatic valence balance ow(r) 1/8 3/6 2x5/6 o}1'(2) r/8 3/6 2x5/6 2.29 limits the number of cations which can cluster about an anion. An octahedrally-coordinatedMe3+ cation F 2x3/6 1.00 contributesbond strengthsof316 e.s.u.(electrostatic KAMPF: MINYULITE 261

Tesle 7. Preparationof minyulite(product T), Al leucophosphite(product HH) andFe leucophosphite (productI)*

Minlul ite Al.-leucophosphite Fe-leucophosphite

Phosphate digested AI, A!, Fe Cation in solution K K K

tPo;-l (M) 1.0M 2 . OT,I 1.0-3.5M tF-l (M) 0.1M

Final pH 2.8 5.0 2.5-6.0 Temperature (oC) 95 145 75-l4S Tine (days) 2T 50 1A al

Enpirical fonnula KzO'2Alz0:'2PzOs' KzO'2A9'zOg'2P 20 5' KzO.2FezOs'2PzOs' I . 6HF'62HzO 5H20 5Hz0

Hasernanet al. (1950).

units)to eachof its ligands.For a bondconfiguration strongeraffinity of Fe3+for (OH)- than for F- sug- to be stable,the chargeof the anionmust be approxi- geststhat the Fe8+analog of minyuliteis not likely to matelybalanced by the sum of the bond strengths exist. which it receives.It is apparent that perfect elec- The Al-F-Al linkageis probablyalso important in trostatic valencebalance is attainedwhen F ligates the stabilitiesof a numberof other minerals.Fluellite to two Me3+cations, whereas ligation to three Me3+ is one of particularinterest, since it hasbeen noted in cations would result in severebond strengthover- a phosphate-rockparagenesis similar to that of min- saturationof F by 0.50e.s.u. A somewhatdifferent yulite. The structureof fluellite was shownby Guy situationarises for the (OH)- anion,since this anion and Jeffrey(1966) to be basedon F- corner-sharing is polar and the hydrogenoften forms a weakhydro- chains of Al3+ octahedra.Although some sub- gen bond with another anion. For electrostaticva- stitutionof (OH)- for F is indicatedby chemical lence-balancecalculations, the 02- and H+ of the analyses,the bridgingligand is alwayspredominantly (OH)- anion are consideredseparately. Baur (1970) F-. The chain in fluelliterepresents a greaterdegree proposedthat the 02- receivesa bond strengthof 5/6 of Als+ octahedralcondensation than the dimer in (0.83)e.s.u. from the H+. On this basis,the ligation minyulite, and it is likely to resultfrom a greaterF- of (OH)- to two Mee+ cations results in under- concentration. saturationof the anion by 0.l7 e.s.u.,whereas liga- The occurrenceof minyulite in soils is strongly tion to three Me3+cations results in oversaturation dependenton the presenceof F-. SinceF- is gener- by 0.33e.s.u. ally not prevalentin soils,minyulite is not likely to be Although the minyulite dimer (2Me3+/anion)is important in the fixation of phosphatein soils.Where clearly preferredover the leucophosphitetetramer F- is locallyabundant, however, minyulite (and fluel- (3Me8+/anion)on the basisof electrostaticvalence lite) are likely to form in preferenceto low-temper- balancealone when either F- or (OH)- actsas the ature aluminumphosphates which do not contain bridgingligand, the preferenceis considerablygreater appreciableF-. when the bridging ligand is F-. The tetrameris ap- Minyulite has not, as yet, been reported from a parently stabilizedby other factors,which are only pegmatite,although both leucophosphiteand fluellite outweighedby electrostaticvalence imbalance when are well-documentedas low-temperaturespecies in the bridgingligand is F-. In Fe3+leucophosphite, the phosphate-richpegmatites. This may reflectthe im- tetramer is probably stabilizedby Fe8+-Fee+spin probabilityof K+, Al3+,POI-, andF- all existingin a coupling made possibleby the close approach of low-temperatureaqueous pegmatitic fluid in suf- these cations. This stabilization along with the ficient concentrationsto permit its formation. 262 KAMPF. MINYULITE

Acknowledgments computedfrom numericalHartree-Fock wave functions.,4cla I wishto thankJ. E. Johnson, ofthe South Australian Museum, Crystallogr,A24, 321-324. L., Nunzi,P.F.,Zanazzi and A. R.Zanzari (1973)The for supplying the exceptional crystals of minyulite used in this Fanfani, A problem:the crystalstructure of a ferrian copiapite. study and Professor P. B. Moore for many fruitful discussions. copiapite 58,314-322. This study was supported by the NSF Grant GA-40543 and an Am. Mineral, (1966)The crystalstructure of NSF Materials Research Grant awarded to The Universitv of Cuy, B. B. and G. A. Jeffrey Mineral 1579-1592. Chicago. flueflite,AIrPO.F,(OH).7HzO. Am ,51, Haseman,J. F., J R. Lehr and J. P. Smith(1950) Mineralogical characterof some iron and aluminumphosphates containing potassiumand ammonium. Soil Sci. Soc. Am Proc, 15,76-84. References . Moore, P B. ( 1970)Octahedral tetramer in thecrystal structure of Axelrod,J. M., M. K. Carron,C Milton andT. P. Thayer(1952) leucophosphite,K,[Fel+(OH)r(PO.).] .2HrO. Am Mineral, 57, Phosphatemineralization at Bomi Hill and Bambuta,Liberia, 397-4t0. WestAfrica. Am. Mineral..37.883-909. -and S.Ghose (1971) A novelface-sharing octahedral trimer Baur,W. H. (1970)Bond length variation and distorted coordina- in the of seamanite.,4la Mineral, 56, tion polyhedrain inorganiccrystals. Am Crystallogr Assoc. I 527-l 538. Trans..6.129-155. Murray, C G (1973)Fluellite and minyulite from Wolffdene,near -(1972) Predictionof hydrogenbonds and hydrogenatom Beenleigh,Queensland Gout. Min J , 74,271-2'14. positions i n crystallinesolids. ,4 cta Crystallogr., 82 I , 1456-1465. Simpson,E. S. and C. R. LeMesurier(1933). Minyulite, a new -and B. Rama Rao ( 1967).The crystalstructure of metavaux- phosphatemineral from Dandaragan,W. A. J. R Soc West ite. Naturwissenschaften, 2I, 561-562. Aust. 19.13-16. -and A. A. Khan (1970)on the crystalchemistry of salt Spencer,L. J, F. A. Bannister,M. H. HeyandH.Bennett(1943) hydrates.VI. The crystalstructures of disodiumhydrogen or- Minyulite(hydrous K-Al fluophosphate)from SouthAustralia. thoarsenateheptahydrate and sodium hydrogen orthophosphate M ineral.Mag, 26, 309-314. heptahydrate.Acta Crystallogr,826, 1584-1596. Stewart,R. F., E. R Davidsonand W T. Simpson(1965) Coher- Busing,W. R., K. O. Martin and H. A. Levy (1962)ORFLS, a ent x-ray scatteringfor the hydrogenatom in the hydrogen Fortran crystallographicleast-squares. U S Oak Ridge Natl. molecule.J. Chem Phvs,42, 3175-3187. Lab. (U S ClearinghouseFed Sci Tech Inf.)Rep ORNL-TM- 305. Manuscript receiued,April 2, 1976; Cromer,D. T. and J. B. Mann (1968)X-ray scatteringfactors acceptedfor publication October 22, 1976