Canadian Mineralogist Vol. 15, pp. 3642 (1977)

THE GRYSTALSTRUCTURE OF ROSETITE

F. C. HAWTHORNE eNo R. B. FBRGUSON Dept, of Earth Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2

ABSTRACT 12.968(4),c 5.684(1)4, p 108.05(2).,er les dia- grarnmesde pr6cessionconfirmeut le groupnP21/c. The crystal strugtureof roselite, Cag(Mgb.assCoo$6) (AsO)r.29r9, La ros6lite est isoty?e de la kriihnkite, NazCu- has been refined in the spacegroup (SOr,.2HrO (Ilawthorne & Ferguson P2r/ c (a p L975b). l-z 5.801(1),D 12.898(3),c 5.617(DI"" structure est caract6risdepar des octa0dres isolds 107.42(2)' Z-2), ; lsitg, tlree-dimensionalcounter- Mg/Co, li& par les sommets aux t6traBdres As collected $ngle-crystal X-tay data; the final R index pour former paralldles for des chalnes i l'axe c. Ces 1194 observedreflegtions is 5.8Vo.Comparison chaines sont reli6es par gros of les cations Ca et des the cell dimensionsobtained in this studv with ponts hydrogdne. On trouve types structuraux the 2 axial ratios obtained from morphological stu- parmi les min6raux du groupe dies Culut+(X+O)z @eacock 1936) shows that the morphological .H:O, celui de la ros6lite, monoclinique, celui ceU was B-centred. et Conversely, tle cell derived in do la collinsite, CazMg(Poa)2.2H2O,triclinique. Les earlier X-ray (Wolfe studies 1940) is a haff-ce[ itr deux type,spossddent des chalnes identiques, tho E-centred setting. gs.eaamination mais of the iso- l'orientation relative des chalnes voisines diff0re structural miueral brandtite, CarMn(AsO)r.2HzO, quelque peu, ce qui entralne des changementsdans showedtlat tle cell derived in previous studieswas hatf Ia coordination du Ca et danslagencement des ponts also a cell; least-squaresrefinement of tle hydrogdne. powder diffraction gave patiern a 5.899(2), b (Iraduit par la R6daction) 12.968(4),c 5.684(1)A, p 108.05(2)., and sinele- cryotal precessionphotographs confirmed the space grcurt P2Jc. fNrnopuctroN Roselite is isostructural with tritbnkitc, NazCu Roselite is a pink hydrated arsenate,Caz(Co, (SOJ".2HrO (Ilawthorne & Ferguson 1975b). The Mg) (AsOa):'2Hfi, structure is characterizedby isolated Mg,/Co octa- that occurs with hedra that are linked by corner sharing with As te- and drusy in cavities in metalliferout trahedra to form chains parallel to the c axis. These quartzose veins. There has been a considerable chains are linked together by tle large Ca cations amount of work on the crystallography of rose- and hydrogen bonding. Two structure Epes exist in lite and its isomorph, brand ite (Ca,Mn(AsOa),. the of tle group Ca24W+(X'+O)2.2IJ2O, 2HzO), and each new study has come to a dif- the monoclinic rosette structure and tle triclinic ferent conclusion; the present study is no excep- collinsite, CaaMg@O)r.2IIO, structure. Identical tion. Roselite was initially classed as ofihorhom- chai4s exist in both etructuresbut tle attitude of ad- bic (Levy 1824) until Schrauf (1873) concluded jacent chains is slightly different, leading to changes that it was triclinic, pseudo-orthorhombic. Sub- in the Ca coordination and hydrogen bonding ar- rangem€nts. sequently, Lindstrom (1918) proposed that brandtite was triclinic and isomorphic with rose- lite. Aminoff (1919) later proposed that brand- Sopnuernn tite was monoclinic holohedral with the axial ratios given in Table 1. An extremely detailed La structure cristalline de la ros6lite, Ca2(Mgo.a*- (1936) Coo.rrr) (AsOolr.2grq a &€ affilrfp dans p2t/c (a study by Peacock showed roselite to be 5.801(1),D 12.898(3),c 5.6r7G)Iu F rot.ize)b; monoclinic holohedral with axial ratios similar Z-Z) a faide des donn6es tridimensionnelles des to those earlier established for brandtite (Iable rayous X, obtenues sur diffractom&tre i compteur 1). Single-crystal X:ray photogaphs (Wolfe avec cristal unique. Le r&idu final pour les 1194 1940) confirmed the monoclinic symmetry of r6flexions st R=5.8Vo. En comparant le.s dimen- both speciesbut indicated that the morphological sions de la maille ci-dessw aux rapports d,axesmor- studies had resulted in a double cell. These re- phologiques@eacock 1936), on remarque que la sults were apparently confirmed for brandtite by maille morphologique 6tait i face B centr6e. Par Dahlman (1951), who solved the structures of contre, la premibre maille obtenue aux rayons X brandtite and krohnkite CNarCu(SO)r,2HrO)i (Wolfe 1940) n'6tait qu'une demi-maille !. Et la the cell dimensions obtained by Wolfe (1940) brandtite, Carl\r!(Asotr,2f|.zA, isotfpe de la ros6- given lite, avait, elle aussi, 6t€ rapportde i une demi- and Dahlman (1951) are in Table 1. As maille; faftinement du diagramme de poudre par part of a study on the stereochemistry of the moindres car6s donne la maille: a 5.899(2), b (Ass+Oo)s group (Ilawthorne 1976a,b), we de- 36 CRYSTAL STRUCTURB OF ROSELITB 37 cided to refine tle sftucture of roselite; how- Ercrx,nvreNrer, ever, in view of the results obtained, the study was also extended to include brandtite. The crystals used in this investigation are from Schneeberg Germany. A partial chemical anal- ysis was performed and the results are given in 1ABIJ 1. axrAl nATlos Ar{DcqLL Drmsrons 1t1 ror nosrrrm, nratr IITE ANDKIOE!{KIIf, Table 2; unit-cell contents were oalculated as- suming the formula CarMg,Co),(AsOn)".2HaO qbcB;::$Rere,ence with the MgCo ratio derived from the chemical analysis. RoeeL:Lte Single-crystal X-ray precession photographs 0.8780 1.0 0.4398 100.9. Monoc. Pacock (1936) confirmed the monoclinic stmmsfry established s.ooi rz.so! 5.60 100.8" p2lla wolfe (1940) by earlier studies. Ilowever, the unit cell ap- 5.616(2) 12.893(4)11.277(3) 1O1.OL(3)o 821la This srudyl peared to be twice the volume assigned by Wolfe (1940), ,agreement s.799 12.893 5.616 L01,37" P2rla ThLe erudy2 with axial ratios in with the morphological work of Peacock (1936). The s.80r(1) 12.898(3) 5.6L7(D 707.42(2). rhls study3 "2rlo following systematic extinctions were observed: Brandt!te hkl, h+l = 2n*I; hoo, h=2n*l; ok0, k= 0.4720 1.0 0.4475 99.5" Moooc. lotnoff (1919) 2n*I;001, I=2n*l; this is compatiblewith the 5.65 12.80 5.65 99.5. p2rla Dahl@ (1951) space groups BL/a ar;ld.BLlc, As indicated by

s.6a4 12.968 11,399 roo.24o E2tla rhlo atudy4 the B-centring, an alternative primitive cell of have been chosen; how- 5.899<2) L2.968(4) 5.684(1) ).O8.0512)" p2rla Thte etudy3 half the volume could ever, the B-centred cell was retained becauseof Kaohoklte tho probable relationship between the structures 0.4586 1,0 pslache 0.4357 108.5' Uodoc. (1936) of roselite and brandtite @ahlman 1951). Unit- 5.eO7O) 12,656(2) 5.517(1) 1A8.32(L)o P2./a n&bode - & cell parameters were determined from least- Fe!8aon (1975b) squares refinement of fifteen intense reflections _Shg1e-crystaLI zttdsfomed dlf f racrreter results; fM B-c@treal aligned automatically on a four-circle diffracto- -froo the results given in Table 1. As a !o ptbLtlge cell; least-sq@les lefl!(@t ol pdde, pettem; meter; are Alroefosd check on these values, the powder pattern of f,!@ prleltlve cell ro A-ceotreil cell, roselite was recorded using a Phillips powder diffractometer operating at Veo2|/rnrn and using = TABLE 2. MISCEI.I,ANEOOS INFORMAIION FOR ROSELITE C\rKa radiation (l 1.5418A); least-squaresre- finement subsequently confirmed the single- crystal diffractometer values. - PaltiaL Analyslsz V€O 4.42, CoO - 8.71 vt.Z The crystal used in the collection of the in- Unlt fo@ula - C"2 (MBo. (As04)2. 2I{20 4g5CoO.515) tensity data was an irregular equidimensional fragment -O.15mm in diameter. A total of 1521. A2Lla p2L/c intensities was collected over one asymmetric a 5.616(2)R sJsge)8, unit out to 2|(MoKa) 65o according to the ex- b 12.893(4) 12.893(4) perimental procedure of Hawthorne & Ferguson c 77.277(3) 5.616(2) (1975u). One standard reflection was examined p ror.or(:)o rol.:z(:)o every 50 reflections to check for constancy of Space cloup R2Lla P2Llc crystal alignment; no significant change was v 8oo.g8' aoo.sR' noted during the data collection. The data were conected for absorption, Lorentz, polarization and background effects and converted to struc- lo. or I52I lr"o,l ture factors. A reflection was considered as ob- D"u1. 3.617 No. of 41 1194 lroU"l) served if its magnitude exceeded that of four Cryetal Slze 0,15@ Flnal R (obBeryed) 5.82 standard deviations based on counting statistics; 0.84 Flnal R (a11 d,ata) 6.12 1.R application of this criterion resulted n ll94 Radnlon t4o/C Flnal R!(observed) 6.72 observedreflections. Flml Rs(all- data) 7 .32

* -f,rlr.o"l- 1'".r"1y'f, p.o,; Srnucnrnr SolurloN eNp RenNnMeNr 2,\ R'V'A' - (I-w( lr . | - lr 1,2/P--- wL--' curves atoms caIQ) )' Analytic scattering for neutral l-obel l fLvro6" (1968) rgg --l were taken from Cromer & Mann with Tsp. factor foft used: nrn: "* /r: anomalous dispersion coefficients fiom Cromer l- _L h I & Liberman (1970). Crystal-structure refine- ment was carried out using the least-squares 38 TTIE CANADIAN MINERALOGIST

TABLE 3. AlO!fiC POSITIONS AND EQUIVALENI ISOTROPIC TTMPETATURE TABI.E 5. SELECTED INTERATO!,flC DISTANCES AND A{GI,ES FOR ROSELITE 1 TACIORS IN ROSELITE tu-o(L)a r.aeo(e)t A€-0(2) r..696(6) ca-o(1)d 2.35s(6)8 B cR2r &-0(3) 1.703(6) ca-0(2) 2.419(6) Ag-0 (4) 1.689(6) ca-0(2)e 2.502(6) ce-0(3)d 2.421(6) (e-o) 1.68e Ca-0(4)d 2.481(6) 0 o ca-0(4)f 2.42L(6) r{e/co o.ze(:) !18,/co-0(2)b 2.197<6) z2 3 0 Ca-0(v) 2.399(6) Mc/co-o(3)c 2.056(6) a2 ltg/ceo(r) 2.060(6) (ca-o) 2.440 0.9498(2) 0. 1216(1) 0.719I(1) ^ 71t7\ 0.5618 0.1216 o.2307 (ue/co-o) 2.104

As 0.45883(13) 0.1203s(6) 0.89194(i) A '.\t,\ A€ telrshedron o.2L6L2 0.12035 0.56689 0(r.)a-0(2) 2.775(8) O(1)a-As-o(2) U1.2(3)" 0.0264(r.r.) 0(1)a-0(3) 2.78s(8) 0(L)a-As-o(3) 11r.5(3) 0(1) 0.1739(s) 0.9422 0.1739 3.i,3lt^"'o.e8(8) 0(r)a-0(4) 2.8rr(8) 0(1)a-As-o(4) 113.7(3) 0(2)-0(3) 2.730(8) 0(2)-A6-0(3) 106.9(3) 0(2)-0(4) 2.787(8) 0(2)-k-0(4) u0.8(3) 0(2) 0.6979(r0) 0.0s31(s) 0.2810 0.0531 3:3i3i,',0.83(8) 0(3)-0(4) 2.64OG) 0(3)-k-0(4) 102.2(3) (0-0) 2.75s (o-A"-o) 10e.4 0(3) o.2239(9) 0.0352(5) 0.2368 0.0352 3:3113,',o.8e(s) )lglco octshedron

0(2)s-0(3)h 2.926(8, 0(2)s-us/co-o(3)h 87.0(2)o 0(4) 0.3528(9) 0.2060(5) 0.7809(5) n cale\ 0.4382 0.2060 0. 5719 0(2)s-0(3)l 3,08s(8) 0(2)s-us/co-o(3)r 93.0(2) 0(2)g-0(!)J 3.186(8) 0(2)s-us/ceo(r)J 96.8(2) 0(2)g-0(w)k o(2)8-us/co-o(c)k 0.5570(10) 0.1385(4) 0.5923(5) 2.828(8) 83.2(2) 0 (r,') n aq/e\ 0(3)h-0(r)J 3.024(8) 0(3)h-Vs/Ceo(w)J 94.7(2> 0.8154 0.1386 o.9647 0(3)h-0(e)k 2.786(8) o(3)h-Mslco-o(e)k 85.3(2) (o-o) 2.973 (o-.{s/co-0) 90.0 IUpper t"luee are fo! B2l/ai lorer va1ue6 are for !2r/c. Ce polvhedron

0(r)d-0(2) e 3.511(8) 0(1)d-ca-o(2)e 92.3(2) o (1)d-0 (4)d 3.102(8) 0(1)d-ca-o(4)d 79.4(2) program RFINE @inger 1.969); quoted R- o (1)d-0 (4)f 3.533(8) 0(1)d-ca-0(4)f 9s.2(2> 0 (1 ) d-0 (r) 2,896(9) 0(1)d-ca-0(r) 74.9(2) indices are of the form given in Table 2 and 0 (2) -0 (2) e 2.978(71"',) 0(2)-ca-0(2)e 73.4(2) are expressed as percentages. 0(2)-0(3) 2.926(8) 0(2)-ca-0(3) 73.2(2) 0(2)-o (4) f 3.387(9) 0(2)-ca-0(4)f 87.5(2) Initially, \re tried to derive a structure modei o(2)-o(o) 3.164(8) 0(2)-ca-o(w) 80.9(2) 0(2)e-0 (3) 3.442(8) 0(2)e-ca-0(3) 88.6(2) by assuming that roselite was a modification 0 (2)F0 (4)d 4.619(9) 0(2)*ce-0(4)d L35.6(2) of the brandtite structure (Dahlman 0 (2)e-0 (r) 2.828(8) 0(2)e-ca-0(r) 70,5(2) 1951), but 0 (3)-o(4)d 2.640(8) 0(3)-cs-o(4)d 65.0(2) this was unsuccessful. Arsenic and calcium 0 (3)-o(4) f 3.981(10) 0(3)-ca-o(4)f 1r0.4(2) 0(4)d-0 (4) f 3.029(5) 0(4)d-ca-0(4)f 76.2(2, positions were subsequently derived from a 0(4) f-0(r) 3.154(8) 0(4)f-ca-0(r) 81.7(2) three-dimensional Patterson map, and yielded (o-o) 3.279 (Gca-o) 85.7 an R-index of 35Vo in the space group B2Ja. Difference fourier maps located the positions r,qulvelent posltl@s: a-l/2*,y,1"/2ki b-l-x, -y, l-zi c-x,y,-2, -y,3/2-z; of the remaining Mg/Co and oxygen atoms, d-lk, y, zi *3/2-x, f-I/2*, I/2-y, zt gpx-L, y, z-Ia y, -y, y, and these were inserted into the refinement, h-x' z-1; 1--x, t-zi J-x-1/2, z-I/2i k-Ll2-x, t, 112-2. yielding an R-index of I1.6Vo. Full-matix Ieast-squares refinement, graduaily increasing to anisotropic of the form given in Table 1 the number of variables, resulted in conver- and a correction for isotropic extinction gence at R- and R.-indices of 7.1 and 7.47o (Zachariasen 1968) was introduced into the respectively for an isotropic thermal model. At refinement Several cycles of least-squares re- this stage, temperafure factors were converted finement gradually increasing the number of variables, resulted in convergence at R- and TuLE 4- Nr$noprc mrtuiw mmons ron nosntrf R--indices of 5.8 and 6.77o (observed reflec- tions) and 6.7 and,7.3/o (all data)'. Final ato- mic positions temper- Ftt [r, / tt /t, /" /,, and equivalent isotropic ature factors are presented in Table 3 and Ug/Co 467<56) 137(11) 167(14) 0 4(22) 0 anisotropic temperature factors in Table 4. 414(36) 139(7) 139(9) -3?(L4t 0(14) 1(7) Interatomic distances and angles were calcu- 184(20) 93(4) 104(5) -10(5) 31(7) -r(4) lated with the program ERRORS '(L. W. 0(1) 1021(79) 146(31) r38(39) -33(58) 18(6r) -16(28) Finger, pers. comm.) and are presented in 0(2) 541(151) r44(29t 189(40) 103(53) 108(61) -4(28) Table 5. 0(3) 583(153) 167(31) 173(39) -106(56) s2(62) r2|c8)

0(4) 355(143) 152(29) 204(40' -2(52) -4(61) 47 (28) lStructure 0(w) 626(151) r37(12) 182(39) -32(54) 81(64) -15(27) factors may be obtained, n1 a a6minsl charge, from the Depository of Unpublished Data, CISTI, National Research Council of Canada, all r,alue x 105 Ottawa, Canada, KlA 0S2. OF ROSELITE 39

DrscussroN Examination of the roselite structure derived in this study revealed that it is isostructural with brandtite and kriihnkite. In the B-centred cell, the corner-linked chains of octahedra and tetrahedra extend along a; howevern if tle cell is transformed to the primitive orientation, 0a'Cw these chains extend along c as in kriihnkite (Hafihorne & Ferguson 1975b). Table L also shows the cell dimensions of roselite in the PLI c orientation. Their similsify to those of krdhnkite is very marked, but the significant differences from the cell dimensions of brand- tite (Dahlman 1951) prompted us to re-exam- ine tlis . Single-crystal precession pho- Frc. 1. The relationship between the different cells primitive tographs of brandtite from the Harstig mine, chosen for roselite. P = cnll,'W B = B- Varmland, Sweden(R.O.M. #M1.19I3) exhibited centred cell" M = morphological cell, ='celf' monoclinic symmetry with systematic absences chosenby Wolfe (1940). compatible with the space group P2t/ c; the cell dimensions wele fairly si,milar to those of by Ca atoms coordinated by seven anions at dis- roselite in the PL/ c arientation. The powder tances between 2364 and 2.50A, in an aug- pattern was recorded from this crystal using prism - mented trigonal arrangement @ig. 3); ad- a Gandolfi carnera and C\rKa (I 1.54184) ditional inter-chain linkage is provided by hydro- radiation, and a least-squares refinement gave geu bonding yiftisl links the octahedron corners the cell dimensions reported in Table 1. In. to the tetrahedron corners in the Ddirection dexed powder patterns for roselite and brand- (Fig. 2). The wealness of the interchain linkage tite (PL/ c orientation) are given in Table 6. in the b-direction results in the {010} The cell dimensions of brandtite are compatible exhibited by the minerals with this structure. with those of roselite and contrast with those reported by Wolfe (1940) and Dahlman (1951). TABI.E 6. NDEXID ?OIDIR PAMINS FOR ROSUIE AND NTIM. Figure L shows the relationships among the cells derived here and those reported by previous n K < o. n Y t d- d - r. workers. The morphological cell of Aminoff (1919) and Peacock (1936) correspondsto the Roeelltel

8-centred cell initially used here (except for an o 6.444 6.449 20 2.057 2.057 5 interch.ange 1 5.089 5.086 2A 2.OO4 2.(nL s of the a and c axes); however, the 0 4.951 4.949 10 1.908 1.906 5 cell dimensions reported by Wolfe (194O) and I 4.335 4.332 10 L.873 7.412 5 1 4.191 4.200 10 1.857 1.858 5 Dahlman (1951) do not conform to a proper 1 3.746 3.745 L.427 L.426 5 1 3.395 3.395 1.812 1.814 L5 cell, but seemto be related to the correct cell by 0 3.356 3.353 60 1.724 1.125 10 -Yz/0 -1 1 3.266 3.268 5 r.72r r.72! r.5 the transformation (1 A 0/001). This is 0 3.222 3.224 1.71.2 1.711 15 rather surprising I 2.993 2.992 100 L.697 1.698 5 in view of the fact that Dahl- 2 2.163 2.763 50 0 t.697 1.698 10 man (1951) arrived at the correct structure for 0 2.683 2.679 J r.612 1.612 5 0 2.625 2.62) 5 0 L.602 1.601 5 brandtite. Examination of the structue factors 2.592 2.590 l5 I 1.568 1.568 5 2.543 2,543 5 L.557 r.557 5 for brandtite listed by Dahlman indicates that 2.326 2.321 10 2 7.496 1.496 10 'half 2.251 2.250 a t.394 1.393 5 this cell' cannot have been used in the in- 2.094 2.tOO t5 o r.376 t.376 5 dexing of the reflectionsnand we are unable to Braadtite2 explain his results. Certainly the observed iso- 6.442 6.444 2.345 2.341 5 morphism between roselite, brandtite and kriihn- 5.151 5.148 20 2.21L 2.259 4.993 4.988 10 2.192 2.t92 kite is far more apparenl from the correct cell 4.403 4.405 10 2.L54 2.L54 dimensions 4.237 4.242 10 2.156 2.L53 reported in Table 1. 3.790 3.796 20 2.118 2.L18 3.424 3.424 30 2.072 2.070 55 7.949 1.949 The structure of roselite is shown in Figure 2, 3.294 3.290 5 t.926 t.927 where the hydrogen bonding 3.247 3.242 70 1.899 1.898 IO has been assumed 3.178 3.176 5 1.874 1.875 to be the same as that previously observed in 3.010 3.Or2 100 L.824 L.824 5 2.799 2.197 5 r.824 !.824 5 kriihnkite (Ilawthorne & Ferguson 1975b). Arse- 2.736 2.734 5 1.735 1.736 LO 2.700 2.702 5 1.716 L.7r6 5 nic tetrahedra and Mg/Co octahedra are linked 2.642 2.645 5 by corner-sharing to form chains that extend 6 lgooder 2&odolfl along the c axis. These chains are linked together tllffractooet.t, I "*". 40 THE CANADIAN MINERALOGIST

T I c

It

F--'/2 b/----a F._bsin*j

ROSELITE COLLINSIT E - Fro. 2. The structures of roselite (left) and collinsite iright). o = Ca, o H. Dotted lines denote hy- drogen bonds.

c I

Frc.3. The coordination of Ca in roselite (left) and sollinsite (right). * indicates the additional anion that moves into the coordination sphere of Ca in collinsite. CRYSTAL STRUCTURE OF ROSELITE 4l

Table 7 summarizes the compositional and tional coordinating anion in the collinsite struc- crystallographic data of the minerals with the ture leading to a biausmented trigonal prism general formula Cazlu?+(X+Oa)z.2HzO. With arrangement. the exception of collinsite, the cell dimensions Bond strength tables for roselite and collinsite presented here were derived from least-squares are shown in Table 8, where the differences in refinement of previously published powder pat- the anion coordinations are immediately appa- terns, as a variety of settingshave been used for rent. Whereas in the roselite structure, the O(1) this group and it was thought desirable to and O(4) atoms are hydrogen bond acceptors, standardizethe setting to that used for collinsite only the O(4) anion is an accepor in the collin- by Brotherton et al. (1974). The similarity of the site structure. In order to maintain the ideal bond 'deserted' powder patterns indicates that only two struc- strength sum around the anion [O(3) ture types are present in this series, the mono- in the collinsite structurel, an additional bond is clinic roselite-type structure and the triclinic formed with a neighboring Ca cation. Ilo\trever, collinsite-type structure. Figure 2 shows that the this does not involye a change in cation coordi- two structures are very similar. Both are charac- nation; ,although the anion arrangements around terized by isolated iW+ octahedra that are linked the Ca cation are topologically very similar in by corner sharing with (Xu+Oa)etetrahedra to both strucfures, the difference in space group form chains of the general stoichiometry (lll+ symmetry involves a re-labelling of the equivalent Xz"*O".2HzO)a-extending parallel to the c axis. atoms in the coordination polyhedron, and it is However, the different attitude of adjacent this that effects the coordination changes around chains in the two structures leads to differences O(3) and O(4) in collinsite. The actual increase in the inter-chain linkage. In the collinsite stnuc- in Ca coordination in collinsite is caused by the ture (Fig. 2), the right-hand chain is rotated occurrence of an additional bond to the O(2) 180" with respect to the corresponding chain in anion [: O(3) in roselite]. The Mg-O(3) bond the roselite structure; becausethe octahedra are is weaker than the corresponding Co/Mg-O(2) tilted with respect to the chain axis, this pro- bond in roselite, due to the much stronger bond- duces a relative displacementof the water mole- ing with the water molecule in collinsite and cules in adjacent chains, leading to a slightly dif- hence the O(3) anion shifts to become part of ferent arrangement of hydrogen bonds. In col- the coordination sphere of another neighboring linsite, the two distinct hydrogens both hydro- Ca cation. gen bond to tle same anion; in order to com- Brotherton et al. (1974) remarked on the pensatefor the decreasein bond strength around unusual nature of the Mg coordination in collin- the remaining sni6as due to this arrangement of site. Whereas in roselite and krdhnkite, the octa- the hydrogen bonding, the coordination around hedron is strongly elongated along the O(2)-O(2) the Ca cation changes slightly and an additioual axis, it is extremely compressedalong the O(5)- anion moves into the coor.dination sphere. The O(5) axis in collinsite. The reason for this is Ca coordination in both structures is shown in certainly not apparent from the bond strength Figure 3; the anion arrangementsin both struc- table (fable 8); the bond strength sum around tures are topologically very similar, the addi- O(5) showsa large excess(0.281 v.u.) over the

rerm Z. MINERALSOr tnr Carlt2+{XSO4)2.2H20 CROI'P

Fonula .(E) a(!) rtSl d-o /" /" Sp.Gr. Ref.

Roeel"l.t€ ca2(co,MC)(As04)2.2H 0 5.801(1) 12.898(3) 5.617(1) 90 Lo7,42(2) 90 --l'- 1

Blaudtlte Ca2llt(As0iZ.2H20 5.899(2) L2.968(4) 5.684(1) 90 108.05(2) 90 --l'- I

/-Roee1lte car(Co,!{e)(As04)2.2[20 5.91S(9) 7.025(8) 5.600(6) 97.5(r") 108.9(r.) 108.4(1) pI 2

Tal-oessl.te Ca2ylq(As04)2.2ll20 5.868(3) 6.985(4) 5.578(3) 97.72(s) 109.15(3) Lo7.52('i) pi 3

Colltnalte Carllg(Polr.2nr0 5.734(1) 6.780(L) 5.44r.(r.) 97.29(L) 108.56(1) 107.28(1) pi 4

Caasldylre Ca2Nt(PO4)2.2820 5.7I 6.73 5.4r 96.8 LO7.4 i.04.6 pi

FalrfleLdlte Ca2(l{n,re)(PO4)2.2H20 5.76(1) 6.96(1) s,sl(1) 95.6<2) 1na 7/?\ rno arr) pi 2

rThis zrefloed 3reflned etudy; fr@ ulndexed p@der pattena glver by Frondel (1955); f!@ data glven by plerror (t964) 4grotherton 5whrte i elq gl (L974): et at. (1967). 42 THE CANADIAN MINBRALOGIST

IA3T,I 8. BOND STRENGTHTABLES^ TOR ROSEI,ITE AND COLLINSITE churgen von Brandtito. Geol. Foren. Forh. 4L, L6t-174.

Rosellte BnorrrrnroN, P. D., MAS[-EN,E. N., PRycB,IvI. W. &'Wmrr, A.H. (1974)z Crystal structureof col- ca Hslco k H(1)2 H'2)2 L' linsite. Aust. J. Chem. 27, 653-656. 0(r) o.323 L.29O (0.387) 1.613(2.000) BnowN,I. D. & Samlor.r, R. D. (1973): Empirical 0.241 - o(2) n 1.205 1.949 boud strength bond length curves for oxides. o-230 ",,*2 Acta Cryst 429, 266-282. 0(3) 0.276 0.37g*2 1.185 1.839 CnoMEn,D. T. & MANN,J. B. (1968): X-ray scat- 0(4) o.239 1,226 1.746(2.000) 0.281 <0.254) tering factors computed from numerical Hartree- 0(5) o.296 0.374*2 (0.613) (0.746) 0.67O{2.026) Fock wave functions. Acta Cryst. A.24, 321:324.

CoLll.Gite & LnenulN, D. (1970): Relativisticcal. culation factors for X- r'k p s(sz)', Il' of anomalous scattering .s(sr)2 rays.J. Chem.Phys,53, 1891-1898. 0. 185 o(1) n roox2 7.2I2 o.21,9 1.915 DaTLMAN,B. (1951): The crystal structures of kriihnkite, CbNar(SOn)r.2HrO and brandtite, 0 (2) 0.145 ^ ^^.x2 1.187 1.846 0. r88 MnCas(AsOa)2.2IJ2O. Arkiv Mineral. Geol. L, 0.250 0(3) 1.268 1.811 339-366. 0.293 o(4) 0.308 r.240 (0.226) (0.226) 1,548(2.000) FlNGrn,L. W. (1969): RFINE. A Fortran IV com- puter progmm for structure factor calculation and 0(s) 0.307 o.426*2 o.7?4 0.'174 0.543(2.281) least-squares refinement of crystal structures. lcalculated 2h"dtog.o fr@ tbe cuees of B!@ & shaooo (1973)i Geophys. Lab,, Carnegie Inst. Wash. (unpubl.). lond stleogfhs ,e!e calculated by aasLgnlag aufflcleBt boqd gtrength to ihe acceptor aBlo! to achl.eve e 1da1 bodd strength FRoNDEL,C. (1955): Neomesseliteand beta-rose- s@ of 2.0. B@d €fleogthg ale 1D valerce units (v.u.). Iite: two new members of tle fairfieldite group. Amer. Minerul. 30, 828-833. ideal value of 2.O, and the disposition of hydro- HewrnonNr, F. C. (1976a): Refinement of the gen bonds to both donor and acseptor anions to- crystal structure of adamite. Can, Mineral. !4, getler with the bond strengtls calsulated around 143-t48. the Ca and P cations suggestthat the octahedron (1976b): Refinement of the crystal struc- should be strongly elongated alory the O(5)- ture of beseliite. Acta Cryst, 832, 1581-1583. O(5) axis. Much more satisfactory bond strength & Fencuso\ R. B. (1975a): Refinement sums are attained if it is rassumedthat H(51) of the crystal structure of cryolite. Can. folineral. forms one very strong hydrogen bond with L3, 377-382. O(4) and H(52) forms a weak hydrogen bond & _ (1975b): Refinementof the with O(3), thus accounting for the \iery com- crystal structure of kriihnkite Acta Cryst, BgL, pressed nature of the Mg octahedron in collin- 7753-1755. sitg which may be seen as a result of the strong Lrw, A. (182y'.)':Account of a new mineral sub- H(51)*O(4) bond. Although this is rather spe- stance.Ann. fhil.24, 439442, culative, the bond strength model for the hydro- Lnosrnou, G. (1891): Mineralanalyser.Geol. Fo- gen bonding anangement pro,posed by Brother- ren. Forh.78, 123-217. ton et al. (1974) does depart much further from PsAcocK,M. A. (1936): Oo roselite and tle rule ideality than is generally encountered in inor- of highest pseudosymmetry. Amer. Mineral, 21, ganic structures. An infrared study of these 589-602. speciesmight resolve this point. ScrnAuF,A. (1873): Zur Charakteristikder Mine- ralspecies Roselit. Tschermak Mineral. Mitt., AcrNowrsDcMENTs 291-293. Wrurs, J. S., HnwonnsoN, E. P. & Mesox, M. (1967): Secondaryminerals produced by weather- We pleased are to acknowledge the coopera- ing of the Wolf Creek meteorite. Amer. Mineral. tion of the Materials Research Institute. Mc- 52, Lt9G-Lt97. Master University, Hamiltono in the collection Wolre, C. (1940): Classificationof mineralsof of W. the intensity data, and the National Research the type As(XO)r.nHlO, Amer. Mineral. 25, Council of Canada and the Universitv of Man- 738-753. itoba for expediting our cash flow pioblems. ZecnenresrN,W. H. (1968): Extinction and Boor- man effects in mosaic crystals. Acta Cryst. A2E, RsrsRENcns 42t-424.

AMTNoFF, G. (1919) : Kristallographische Untersu- Manuscriptreceived June 1976,