AmericanMineralogist, Volume63, pages520-527, 1978 rhecrvstar structure *l',l;ff ca2HPO4so 4'4H2o', "t ;:[ll# ?ltrl:f,i:ilHff ,[*ate, TosurnoSnrnn Depafiment of Oral Histology Nihon Uniuersity Matsudo School of Dentistry Mqtsudo, Chiba, Japan Hrnossr Necntr Geological and M ineralogical Institute Faculty of Science, Tokyo Uniuersity of Education Otsuka, Bunkyo, Tokyo, Japan exo Tosuro Suoo Miyasaka3-20-7 Setagayo,Tokyo, Japan Abstract The syntheticcalcium phosphate-sulfate hydrate, CarHPOnSOr.4HrO, is monoclinic,space group Cc, a = 5.721(5),b : 30.992(5),c : 6.250(4)A,and B : 117.26(6)',Z : 4. The structurehas been determinedby the Pattersonmethod and refined by full-matrix least- squaresmethod to a conventionalR : 0.068,using 268 independent reflections. The structure possessesfour sheet-structureunits parallel to (010),in whichCa atomsare coordinated by six oxygenatoms belonging to (P,S)O.tetrahedra and two watermolecules at the surfaceof the sheet.Each sheetunit is analogousto thoseof brushiteand gypsum,but thereis a different mode of sheetstacking from thosein brushiteand gypsum.The mean 7-O bond lengths, I .50A at ?'(I ) siteand I .49A at T(2) site,are close to an averagedistance of P-O ( 1.54A)and S-O ( 1.46A)bond lengths. The distributionof P and S atomsin T sitesseems to berandom. Introduction that X-ray powder diffraction patternsof ardealite, Ardealite, CarHPOnSOl.4HzO,is a rare phos- brushite,and gypsumare considerably different from phate-sulfate mineral first describedby Schadler eachother. Ferraris(1969) insisted that brushiteand (1932) from Cioclovina cave, Transylvania. This gypsum are not in a strict isostructuralrelation be- original material is found in closeassociation with causeof the different spacegroups: /a for brushite gypsum, CaSOn.2H2O,and brushite, CaHPOn. and I2/a for gypsum. Recent X-ray and neutron- 2H2O.Recently, one of the authors(T. Sakae)found diffractionanalyses have revealed that the configura- ardealite from the Onino-Iwaya limestonecave at tion of watermolecules in brushite(Curry andJones, Hiroshima Prefecture,Japan (in preparation). 1971)is quite differentfrom that of gypsum (Cole Beevers(1958) and Hill and Hendricks(1936) and Lancucki, 1974).The crystal-chemicalrelation pointedout that, becauseof a closesimilarity in their amongardealite, brushite, and gypsumis a matterfor chemical compositions,ardealite may belong to a further research. solid solution betweenbrushite and gypsum.In the The study of the crystal structureof ardealiteis crystalstructures of brushite(Jones and Smith, 1962) significantand interesting.It was difficult, however, and gypsumlAtoji and Rundle,1958), the corrugat- to obtain a singlecrystal of ardealitefor structural ing sheetsstack along the b axis.O'Daniel (1939) and determination.Single crystals obtained from syn- Baynham and Raistrick (1960),however, reported thetic materialhave been used in this structuredeter- 0003-0Mx / 78 / 0506-0520s02.00 5201 SAKAE ET AL.: CALCIUM PHOSPHATE-SULFATE HYDRATE 521 mination.These synthetic crystals almost agreewith hkl with h + k : 2n -r I and 0k0 with /c : 2n -r I tead natural ardealite in various properties, but are to the spacegroup of Cc or C2/c. The occurrenceof slightlydifferent from ardealitein their X-ray powder 0k0 reflectionswith k : 4n only (040,080,0120, etc.) patterns. suggestthat the periodicityalong the D axisoccurs at four times the elementaryunit, as describedlater. Experimental Latticeparameters are determined and refinedto a : 5.721(5),b : 30.992(5), 6.250(4)A,p Material 117.26(6)"by least-squaresmethod, using 16 reflec- Ca(OH)2, NarHPOn.l2H2O,and NarSOnwere tions measuredon a Phillipsfour-circle diffractome- usedas startingmaterials. Each of thesewere made ter (graphite-monochromatizedMoKo- radiation). up in water solutionswith the samemole concentra- For intensitymeasurement the o-?i scanningtech- tions.These solutions were mixed with eachother in nique wasemployed (0.05' per secondin <.r).Scan- the moleratio of Ca/(P + S) : l. The pH valuesof ning width wasdefined as a I b(tan|)where a = 1.5 the mixed solutionswere controlled by addingdilute andb : 0.5.The crystalwas so smallthat 400 reflec- hydrochloricacid. Varyingthe conditionsfrom pH 2 tionsto sin|/\: 0.7 werecollected with monochro- to 5; P/S, 0/10 to l0l0; mole conc.,0.25 to 0.5; matized Mo.l(a radiation. Finally, 268 independent temperatures,OoC to 50"C, three-componentmix- reflectionsof lf.l greaterthan 4loF,l wereused for turesof brushite,ardealite-like material, and gypsum the followingstructure determination. The data were were not found in precipitatesalthough two-com- correctedfor Lorentzpolarization factors, but not for ponent mixtures were found. In the seriesof syn- absorPtion(p : 15.35cm-'). thesesat pH 4, precipitatesare brushiteplus ardeal- ite-like material(P/S : 6/4), ardealite-likematerial Structureanalysis plus gypsum(P/S : 5/5), andgypsum (P/S : 4/6), The lattice parametersof the presentcrystal are as revealedby X-ray powder diffraction analysis.A similar to those of gypsum and brushite(Table I ), crystallineprecipitate from a solutionwith P/S : 9/1 exceptthe b dimension,which is nearlyequal to the and pH : 3, after standingfor 43 daysat 20oC, sum of the b dimensionsof gypsumand brushite. consistedof the ardealite-likematerial free from One-dimensionalPatterson synthesis along the 6 axis brushite and gypsum, as revealedby X-rays. This shows a similar pattern to those of gypsum and crystallineprecipitate was used for the presentstudy. brushite, but with a repeat of one-fourth of the b Chemicalcomposition of the productis asfollows: dimension.The resultslead to an assumptionthat the CaO,32.5; P2Ou,20.9; SOs, 23,2; ignition loss (below crystalhas also a sheetstructure, in which eachsheet 600oC), 22.9; total, 99.5 (weight percent). Several stacksalong the b axiswith a four-fold periodicityin crystalsin the product were analyzedsemi- contrast to a two-fold periodicity in gypsum and quantitativelyby the point-analysismethod employ- brushite. ing HnecHr-Krvrx Snna.Each of them had the mole The spacegroup is Cc in brushite(Ia by Jonesand ratio of Ca:P:S : 2:l:1. Althoughthe chemical Smith, 1962)and C2 / c in gypsum(12 I a by Atoji and compositionsof the crystalsare uniform, Weissen- Rundle,1958), and Cc or C2/c in the presentcrystal. berg photographsof the crystalsshow some differ- Ifthe structureis a sheetstructure analogous to those ences.Throughout the photographsthe cell dimen- of gypsum and brushite,a possiblespace group for sionsare the samebut the extinctionsare different. the crystalis Cc rather than C2/c, becausethe sym- Among them a crystalshowing the extinctionsset out metry of the structuremay be reducedon accountof belowwas usedfor the datacollection. Crystals with the presenceof H atoms,as in the caseof brushite. other extinctionsare alsobeing studied. Further, the Thus the spacegroup Cc was examinedin the first single crystal was analyzedby the point analysis stepof the crystalstructure analysisl. method,which confirmed that it hadthe moleratio of A structuremodel having the spacegroup Cc may Ca: P: S = 2: I : l. Thechemical formula was therefore be constructedin the followingtwo ways:(l) one- assumedto be CarHPO4SOo.4HrO. sheetstructure unit is locatedbetween n and c glide Data collection 1 The crystalis a triangularplate (fragment) For the sake of the comparison of lattice parameters between approx- the present crystal, brushite, and gypsum, Cc lattice was selected. imately0.015 mm thick,0.06mm alongthea axisand When Ia lattice for the present crystal is selected, the lattice param- 0.09mm along the c axis.The systematicextinctions eters are a : 6.248, c : 6.250A,and B : 125.52. 522 SAKAE ET AL.: CALCIUM PHOSPHATE-SULFATE HYDRATE Table l. Crystallographicdata for CazHPOrSOn.4HrO,brushite, and gypsum CaTHPOOSO Brush i te Gypsum 4.4HZO Beevers (1958) Cole + Lancucki This study Jones + snith (1962) (re74) 5.727(s)x A 5.81210.002 A 5.670r0. 002 A b 50.992(s 15. 180r0.003 15.201t0.002 c 6.2s0 (4 6.239!0.002 6. 533r0.002 R 1L7.26"(6 1t6.42"r0.03 118.60"t0.07 Cel1 volune 985.1(9) A' 493 A' 494.4 A" Chemical forrnula CazHP04SO4.4H2O CaHPOq .2HzO CaSOo.2HzO Ce11 content 4 4 Space group Cc fa I2/a *Estimated standard deuiations are giuen in paz,entheses and nefet, to the Last decimal place. planes, and the mode of sheet stacking is controlled least-squaresmethod using UNtcs program (Sakurai, by these symmetry operations; and (2) two-sheet 1967,after Onrr-s written by Businget al., 1962).The structure units are located on z and c glide planes neutralatomic scattering factors (International Tables respectively;in this casethe mode of sheetstacking is for X-ray Crystallography,1962) were usedfor Ca, P, not affected by the symmetry operations. In the S, and O atoms.Isotropic thermal factors were set at former, a strong peak should occur at (0,50,0), Ca, 1.4;P andS, 1.0;O, 2.0;HrO,2.5.Inthe succes- coordinates multiplied by 100, in three-dimensional sive refinements,an averagedfactor of P and S was Patterson synthesis, but such a peak could not be usedfor the atomsat the Z sites. observed.A strong peak at (8,17,16) may indicate The positional parameterswere divided into sev- that the positionsof Ca, P, or S atoms in the adjacent eralgroups, becatise the number of variableswere too sheetshave shifted to a and c directions. Such a shift many comparedwith the numberof reflections.Each cannot be expectedin the former but favors the latter. group of positionalparameters was refined separately At this stage of the three-dimensional Patterson