American Mineralogist,Volume 70,pages 171-181,1985

2*Ivl2* crystal chemistry of the 6z$oc)zl sheet:structural principles and crystal structures of ruizite, macfallite and orientite

Pe,ul B. Moonn, JrNcnue,u SuBNI eNo Tereuenu Anerr2 Department of the GeophysicalSciences The University of Chicago Chicago, Illinois 60637

Abstract

The crystal structures of ruizite, CarMn]*1OH)2[Si4Oil(OH)2].ZH2O,monoclinic, a=9.064,b:6.171,c:11.9764,F:91.38',spacegroupC2lm,Z:2,R:0.084for1546 independe-ntFo; macfallite,CazIr,tnS*(OH)3[SiO4Si2O7], monoclinic, a : 10.235,b = 6.086, c:8.9704, F:ll0.75",spacegroupP2ylm,Z:2,R=0.l84for2437independentFo;and orientite,Ca2Mn2+Mn]+(OH)4[Si3Oro], orthorhombic, a : 9.074, b = 19.130, c : 6.121A, spacegroup Bbmm, Z : 4, R : 0. 156for 1238independent Fo, havebeen approximately determined. Structure disorder (domains, intergrowths) and/or solid solution probably affect these structures; and true single crystals of these and related compounds are very infrequently encountered. Ruizite, macfallite, orientite, lawsonite, sursassite,ardennite, pumpellyite, santafeite and bermanite all are based on the same fundamental building block, a sheet 3tttti*16(fO izl, Q : anion not associatedwith a tetrahedron,n : vacancy.This sheet is basedon a layer of the spinel structureprojected down [ 11]giving the 3tM1*d2OO4)21 sheet with maximal two-sided plane group symmetry lp3mll, as found in . Ordered vacancies lead to the fundamental building block in this study with plane symmetry lc2lml. Alternatively, the chain component of the fundamental building block (f.b.b.) is IttvtS*(Or)u(d2l where { usually is OH-. A variety of interchain tetrahedral polymers can occur and many explain the disorder in these structures.

Introduction Structural principle Although many of the crystal structures are The underlying principle is a two-sided plane, a section presently known, the principles behind them are rarely of the familiar arrangementof spinel, Al2(MgOa),normal applied, and a holistic structural genealogy is woefully to [ll]. In our model, the symbol M refers to cationic lacking. Much of the inability to evolve a structural speciesin octahedral coordination (in this case Al3+.;and genealogystems from the difficulty of applying graphical T refers to the cationic speciesin tetrahedralcoordination enumeration to these problems, and the problem of (in this caseMg2+). For spinel, a : 8.14, this arrange- choice:just which part of the structure should be empha- ment has t1 %rt a 5.7A and h : 13 sized?We chooseto demonstratethat a fragment-in this h :9.94.It is an orthogonalcell and hasbeen extensive- case a two-sided slab.-is common to several crystal ly exploited for structures derived from spinel by selec- structuresof , and may afford a unifying genealo- tive site orderings. This arrangement is a sheet with gy among these compounds.The list is by no means composition 3[tr,trOr(too)2], maximal point symmetry exhaustive: the compounds selected were those with $ZtmY witn two-sided plane group piZlm. The nearest reasonablyrefined parameters. Briefly, orthohexagonalmonoclinic subgroup of this would have the compounds occur in regimes of low to intermediate point symmetry lZlm\ and two-sided plane group c2lm. temperature, and low to high (cf. lawsonite) pressure. Table I outlines the crystal chemical characters of these 6 x 9A sheet structures. called such becausetheir axial translations approximate these integers. Of the ten ' representativestructure types, only the structure of san- X-ray Laboratory, Graduate School, Wuhan College of 'tafeite Geology,Beijing, China. is unknown. It is inferred to belong to this group 2 Department of the Geological Sciences, University of Illi- and an approximateformula is given. Earlier, we attempt- nois, Chicago, Illinois 60680. ed to solve its structure but it appears to be twinned, in 0003-.004)vE5/0I 02-0 I 7 I $02.00 t7l t72 MOORE ET AL: STRUCTURES OF RUIZITE, MACFALLITE AND ORIENTITE

Table l. Crystal-chemicalcharacters ofthe 6 x 9A sheet structuresr

Specles g(i) b(i) !-(l) g spqceGrcup t,/tl Trc-slded Dlam Reference l{a0z(T0r ) z '1.740 Chlori told Fe(tI )rAl(0H)rlAt 30r(si04)rl 5.47 18.19 l0l,57' CZlc p3ml Theoreti cal lt't.Oz(TOr)zl,splnel ap = 8.'| A tr = 9:21 \2-fJlL=W lPill, c2ln] |.732 ' czln

MzBz(TOt) r Lawsonlte 4 cafA'lz(0H)z(Slz0r)].H20 5.80 8.83 13.20 Cmm 1.522 c2/n Sursassite 2 iln(il)rlAlr(0H)3(St0{)(sir0?)l 8.70 5.f9 9.78 108.87 P2 ln I.503 P2ln '1.499 Ardennlte 2 iln(II)+Mgr(0H)rtAl {(0H)+(Aso.) (st0r)r(st r0to)l 8.71 II E' Pnm Pzln 4 Pumpellylte 4 Carr'rglAlr(0H)r(sl0r)(Sir0z)l 8.81 5.94 19.t4 97.60 Az/n 1.483 Pzlil orienti te 4 caro(Hr0)rlr4n(III)z(Oft)u(si r0ro)l 9.01 19.13 6.12 Bbm 1.482 bzln o ihcfal I i te 2 carllln(Itl)3(0+r)r(si0r)(siz0z)l 10.23 5.09 4.97 t10,75 P2tln 1.473 PZln Ruizite 2 cartr,|n(tII)r(0H)z(str0rr(0H)z)l.2Hz0 9.05 6.t7 11.98 91.38 Czln 1.158 czln

Santa fe i te 4 a. [hrca(0H)zll.tn(IIr)r(0H)s(v0+)a].H20 9,25 O.JJ 30,00 C222r(pseudo ?) 1.461 cz Bemnite 4 iln(II)(H,0)rtrh(III)z(0+l)z(P0r)zl 6.22 8.93 ra 25 C222r(pseudo) 1.436 cz tspecles are arranged according to decreasing trltr ratJo. Cell edges of the f.b.b. are underllned. The spacegroups of bemnlte and posslbly santafelte are the trlnred groups. The tm-sided plane refers to the f.b.b. 'ln the structures. lHarrlson and Brlndley (1957). zRumnova and Sklpetrcva (1959). 3lGlllni and flerllno (1982). 4Donnayand AllEnn (1968). scottardi (1965). 5Thls TSun study. and $leber (1958), wlth !and gaxes lnterchanged. sKampf and t'loore (1976), after transfomtlon a = [l0l], l = [lOi], c = [OI0]. ilote B" 90.250,

much the same fashion as bermanite. The actual space repeatswas not required. This adds somecredence to the group of bermanite is P21, but twinning usually leads to M2nd2GO4)2unit as a fundamental building block. The the C2221spacegroup (Kampf andMoore, 1976).Ruizite, direction normal to this sheet is the basis of a variety of formerly proposed as Pztlc by Williams and Duggan tetrahedral polymerizations, as we shall see. (1977), is C2lm for our crystal from Kuruman, South Figure 2a is a construction of the idealized Cllm sheet Africa. The "theoretical" structure, which is included in showing the important symmetry operations. Note that the M3@2(TO+)z (d : arbitrary symbol for an anion) all populated octahedraare basedon the unit M(Or)+(d)2, subgrouping, would be a slab of the spinel stmcture where @ are in trans arrangement with respect to the normal to the [111]direction. The spacegroup P3ml for this two-sided plane includes the orthogonal component of CZlm as a subgroup. The sheet of cubic close-packing is the basisfor the ratio tzltt : tfltt : 1.732. An outline of the P3ml, ar = 6A, arrangementis presented in Figure 1. This sheet consists of rows of populated octahedra alternating with rows of insular octahedra and the tetrahedra. Chloritoid actually pos- sessesthis slab as the [AlrOz(SiO+)z]unit and distortions lead to monoclinic or triclinic symmetry, but the tzltt ratio is close to V3. If rows of populated octahedra alternate with rows ofoctahedral voids and the tetrahedra,then the formula M2!6(TO4)2 obtains, where ! is a vacancy. This arrangement is an ordered subgroup of P3zl. Its maximal space group is CZlm. The most pronounced distortion in these structures arises from cation-cation repulsion effects across the shared edges-and a subse- quentdiminution in the t2ltl ratio. lf a = 9A and b : 6A, then t2lt1: 1.50,close to the average1.482 for the nine structure types of M2!+2(TO4)2. The range is 1.545 to 1.428for these compounds.No attempt was made to x transform the cell criteria in Table l. Rather, the 6 9A Fig. l. Sheet of 3[M3dr(To+)z] showing some of the axes were underlined and the ratio was derived directly symmetry elementsin space groupPlml and the unit cell outline from knowledge of the structure and orientation of the with a1,a2- 6A.Some symmetry elements m,7,2,21 andaxial octahedralchains. All the structures approximatethe 6 x glides are shown and are slightly offset to ease visualization of 9 module, and division or multiplication of these axial the sheet. MOORE ET AL: STRUCTURES OF RT]IZITE, MACFALLITE AND ORIENTITE r73

Fig. 2a. sheetof 3[Mrf]hToq)) showinsm,10),1e),2,2, anda-axial glides in spacegroup C2lm, the ordered subgroup of Fig. 3. The hypotheticalstructure built of cis-M@2Oao P3nl. This is the fundamentalbuilding block for the structures octahedra.The symmetry elements m,I areshown and the space in the text. The axesare approximatelya : 94, b : 64. groupis P2lm.The axes are approximately a = 4.5Aand b: 64. octahedralcenter. Monoclinic same-cellsubgroups of this lar orbital for /Mn3* in high spin configurationforces the spacegroup include trans arcangement,but this does not rule out the crs arrangementfor some isotropic cation, say Al3+. Alm --> C2 --->P2, P2r In every structure involving Mn3+ (orientite, macfal- l\ ..+pm lite, ruizite, bermanite), a common feature of polyhedral I r- distortion appears: the polyhedron is elongate with PZlm, P2llm 4Mn3*-O ca. l.%A and 2Mn3*-O ca. 2.21A, with t6l14n3+-6= Often, it is more convenient to project the structure down 2.024 average(Table 2). The major compo-- the shortest axis, frequently an axis of symmetry. Repre- nent of the elongate bonds is oriented parallel to the 6A sentation of the sheet down this direction is featured in axis, the direction which is normal to the octahedral Figure2b. Sincethe axis ofprojection is the 6A direction, sharededges in the l[Mn3+d4] octahedralchain. Isolating it coincides with the direction ofoctahedral edge-sharing the sheet of octahedra and tetrahedra in Figure 2, three chains. It correspondsto the I l0] direction of the spinel kinds of ligand arrangementsoccur. The first is (a) 2Mn3+ structure. + lsi4+ and is an 02- ligand.The secondis (b) I Mn3+ + The trans-M(Or)a(4)zimmediately presentsa problem. lsia+, also an 02- ligand. The third is (c) 2Mn3*, Is crs-M(Or)r(d)zpossible? Figure 3 shows such an correspondingto the hydroxyl (OH-) lieand. In each arrangementwith a' = al2, b' = b, maximal spacegroup structure, the elongateMn3*-O bonds correspond to the P2lm. Of the eight known structures in Table l, all ligand at (a). The combination of the direction of cation- involve trans-M(O")a(4)zand the cis-M(O1)a(@)2anange- cation repulsion and the orientation ofthe elongateverti- ment has yet to be found. It is believed that the pro- nouncedJahn-Teller axial distortion from the d,zmolecu- Table 2. Meridional and apical Mn3*-O bonds for the tundamentalbuilding 0""*lrnil:lnite, orientite,ruizite and

i|erldlonal bonds Apical bonds Average

Bernanite titn(I) 1.89 I .9',1 I .95 L96 2.20 2.20 z.ozA Mn(2) 1.89 1.91 t.94 1.95 2.21 2,24 2.02 0rientite rln(l) l el L9l 1.96 1.96 2.20 2,20 2.O2 Rulzl te '1.91 Mn l.9l 1.95 1.95 2.20 2.20 2.02 Macfallite 'I ',l Fig. 2b. Alternative projection of 3[Mzndz(TOr)z], a r,ln(3) l.e4 .94 I .94 .94 2.22 2.22 2.03 frequent projection for the Fig. 5 series. The edge-sharing crand average t.gS A z.z'rI z.ozA lM@rr 6A octahedral chains are normal to the paper. The 9A direction runs from left to right and the intersheet portion runs Range t,SS-t.gOA z.zo-z.zqA from north to south. Heights are given as fractional coordinates rMn(l) in macfalllte excludedbecause lt containssignlflcant (1976). of the 6A direction. aluminun. The bemanite data are from Kanpf and iloore t74 MOORE ET AL: STRUCTURES OF RUIZITE, MACFALLITE AND ORIENTITE ces result in a t2ltl ratio that is relatively small. Indeed, all five structuretypes with the [Mn]+(OH)z(TOa)zlbuilding block possessthe smallestratios amongthe compounds in Table 1. The [tvtnl+(OH)2GO4)2]fundamental building block (abbreviatedf.b.b.) imprints other portions of the struc- ture as well, even though linking units of varying dimen- sionsoccur between the sheets.The fundamentalbuilding block is a portion of a crystal structure which also is an invariant component of several non-equivalent crystal structures. In the structures of ruizite, orientite, macfal- lite, pumpellyite and ardennite larger cations such as Mn2+and Ca2* occur in seven-foldcoordination by anions and the polyhedron correspondsto No. 23 with maximal point symmetry C2v (mm2) in Britton and Dunitz (1973). The polyhedron is reminiscent of the gable disphenoid of Fig. 5c. Representationof the disorderedorientite structure order 8 which occurs as the coordination polyhedron down [001]. Note [SirOro]groups and disorderedMn(2) are aboutCa2+ and Nal* in severalstructures (Moore, l98l). drawnin. The gable disphenoid is constructed by rotating one The on the squarepyramidal side square face 90o relative to the other of two equilateral number 6. coordination but on the trigonal side the two oxygens are trigonal prisms and fusing them together. PolyhedronNo. is the same, resulting in a distorted octahedron' The 23 is obtained by fusing an equilateraltrigonal prism and a replacedby one, O(3) in Figure 4, which represents square pyramid together at the square face, or can be trigonal oxygens are present but their distancesare too long for simply called the monocapped trigonal prism. In every lawsonite, neighbor coordination. Bermanite, which has case,three vertices of a trigonal prismatic componentlink nearest bridgesthe f.b.b.'s by the to verticesbetween successive octahedra in the 6A chain. intersheetMn2*(H2O)4(Op)2, (Op) These vertices are of the type a(xl) and b(x2). The oxygens. polyhedra commonly polymerize to each remainingfour vertices exhibit a variety of coordinations The X@7 edge-sharing.In ruizite they are isolated, since they are the regions away from the f.b.b. Other other through edge dimers in ardennite and orientite, coordinatingcations to thesevertices can be Si4*, 2Si4", but they occur as the terminal square planar bonds are As5*, M2*, M3*-or the vertices can be other ligands where Ca-O of parallel, in pumpellyite and macfallite where they are suchas (OH-) and (HzO). and these structures are featured in the Lawsonitepossesses the samef.b.b. and the interleav- opposed. Portions of ing Ca2* has related but distinct coordination, being of Figure 5 series. The tetrahedrallinks betweenthe f.b.b.'s are interest- ing. The basesof the tetrahedralsegments such as O(l)- O(2)-O(l) in orientite (Fig. 6c) link to the f.b.b. of the samestructure (Fig. 5c). The tetrahedral units are homo- loguesof the linear sorosilicate series [TnOrn*r], where n

r#--q25l \.

Fig. 5a. Representationof the ruizite structure down the [010] Fig. 5e. Representation of the macfallite structure down direction. Atoms labelled correspond to Table 5a. t0r0t. MOORE ET AL: STRUCTURES OF RUIZITE. MACFALLITE AND ORIENTITE 175

Fig. 6a. Tetrahedralinterlayer link in ruizitedown [100].

: I, Si@a;2, Si2fi;3, Si3@1s;and 4, Sia{13.Representa- tives include bermanite and possibly santafeite (n : l); lawsonite (n : 2); pumpellyite, macfallite, sursassite (n = 1,2);orientite (n = 3); ardennite(n : 1,3);ruizite (n = 4). In the Figure 6 series, the tetrahedral units were projected down the 9A axis and their dispositionsapprox- imate the tetrahedral affangement in the rocksalt struc- ture down [100]. For example, the central tetrahedra in ruizite are viewed down the approximate 2-fold rotors implicit in the 4 symmetry; the entire Si4@13unit (Fie. 6a) Fig. 6e. Tetrahedralinterlayer link in macfallitedown [001] can be considered as the fusion of the [Si2O7]dimers in showing[SizOz] and [SiOr]units. pumpellyite, sursassite and macfallite at the inversion center. This point of fusion forces a central Si-O-Si : have been rewritten in Table 3 to stress two critical 180"angle in ruizite. regions: the intersheetmaterial in the first bracket and the The structures thus can be conceived as sheetsof the fundamental sheet or building block in the secondbrack- 3ttr,trlfi(fOa)21 fundamental building block with con- et. To effect this, the structures in the Figures 5 and 6 nected (Ca,Mn2*)6 polyhedra No. 23. In turn, these serieswere inspected. The fundamental sheet was isolat- sheetsare connectedto symmetry-translatedsheets by a ed and subtracted from the formula in Table l. What variety of (silicate) polymers, including (Mn2+(H2O)4)in remained was cross-checkedon the structure drawings bermanite; [Si2O7] in lawsonite; [SiO+] + in [SizOz] and defined as intersheet material. In only one structure, sursassite,pumpellyite, macfallite; [Si3org] in orientite; lawsonite, was partitioning between regions not exact lAsO+l + [SiO4] + [Si3org] in ardennite; and since one extra oxygen had to be added. This was [Si4Orr(OH)t in ruizite. Naturally, portions of these consequently subtracted from the intersheet material. polymers are also components of the fundamental build- Some very interesting conclusions can be drawn from ing blocks. For example, ruizite could be rewritten Table 3. First, sursassite and macfallite are chemically lCaz(HzO)zSi2O3(OH)2llMnl*(OH)2(SiO4)21where the and structurally related as their recent structure determi- first brackets representthe material beyond the border of nations indicate (Mellini and Merlino, 1982;this study), the fundamental building block denoted in the second the major diference being pronounced Jahn-Teller dis- brackets. With this spirit in mind, rhe formulae in Table I tortion in the latter compound. Second, mistakes in the intersheet region should be quite likely among com- pounds which have the samefundamental building blocks and similar metric relations in these building blocks such

Table 3. Partitioningof formulaein TableI into intersheetand fundamentalbuilding blockt

Firct bracket Secondbracket Species ( Intersheet) (f.b.b.) Lawsonite ca(Hz0)(0) - r Al,(0H), (si0r), Sursassite ilne*Al(oH)sio3 Alz(0H)z(Si0r)z Ardennite llnt+ilgz(St)zsi0zAs0r 2Alz(0H)z(si0r)z Pumpellylte Caz(Hz0)ilgSi0s Alz(0H)z(Si0r)z 0r'lenti te ca2(H20)rsl0' tilnl'(on)z(stor)z !+(oH)sio MacFall lte ca2iln 3 unl+(OH)z(Si0r ) z Rulzlte ca2(H20)2slr0r(0H)2 t'lnl+(0H)z(si 0r) z Bemanite Mn'z*(Hz0) r rn l* (ou)z (pOq ) z isantafeite onltted becausestructure is not knwn, 0rlentlti assunEs the memberwtthout llnz+. Note lsomrphism betseen Fig. 6c. Tetrahedral interlayer link in orientite down [100]. sursassite and nncfallite. Lawsonite has negative o)Vgen ln flrst bracket Here, the connected [Si3O,o]unit is shown. to balance charge, 116 MOORE ET AL: STRUCTURES OF RUIZITE, MACFALLITE AND ORIENTITE as [Mnr+(OH)2(SiO4)2]in orientite, macfallite and ruizite. CapeProvince, South Africa (usNv No. 136812),and thesewere We offer evidence here that the structures of the crystals used throughout the remainder of the study' Good agreement used in our study probably representa substantialdegree appearsin the unit cell parameterscompared with the original of domain disorder, since despite structure solution and study by Williams and Duggan(1977), but we do not agreeon the convergence, their final reliability factors were not of space group. Since P21lc is not a same-cellsubgroup of C2lm, without additional study on the type satisfactory quality. caution must be exerted material, since it is possible (though unlikely) that two closely related sp€ciesare involved. Experimental Macfallite and orientite samplesboth were collected by the Theexperimental details of ruizite,macfallite and orientite are senior author on the dumps of the type locality for the former summarizedin Table4. Crystalsof ruizitefrom the typelocality mineral, near Lake , Copper Harbor, Keweenaw at ChristmasMine, Gila County, Arizona, were kindly provided County, Michigan. Great effort was expendedto obtain adequate by Dr. SidneyA. Williams.Unfortunately, they were unsuitable crystals, since the minerals are usually twinned and occur with for data collectionbecause of twinningand very smallcrystal splayedsurfaces. The crystals finally selectedwere deepmaroon size.Shortly thereafter, Mr. JohnS. White,Jr., of the U.S. and transparent.The end-memberformulae in Table 4 for these NationalMuseum (Smithsonian Institution) kindly sent sharp minerals lead to a calculated density higher than observed, due brownprismatic crystals from the N'ChwaningMine, Kuruman, to the presenceofAl3* in thesecrystals (Moore et al., 1979).For

Table 4. Ruizite, macfallite and orientite: experimentaldetails

(A) Crystal CelI Data

Ruizi te MacFalI i te 0rlentite a,A e.064(r) r0.235 (3) e.074(4) b,I 6.r7r(2) 6.086(6 ) re.l30(7) a,I il.e76(3) 8.e70(5) 6.l 2t (s) B, des 9r.38(2) il0.75(3) Spacegroup C2ln P2tln Bbrtn 2 2 4 Fonnula Cazt4nzSl +0 r r (0H) r.2Hz0 Ca2lrln3Sig0r r(0H) a CazMnsSis0ro(0H)r p(calcd),g cm-3 2.89 3.53 3.48 ? tt Specific aravity* 2.9 3.43 U, Cfi-r 3l.7 50.9 50.I

(B) Intensi ty l\leasur€ments

Crystal size, m 0.30,0.15,0.12 0.15, (lla, llb, llc) irtax(sln e)/r 0.72 0.70 0.70 Scan speed (deg per mln) 2.0 2.0 2.0 Backgroundcounts ------Statlonary, 20s at beglnningand end of scan------Radiati on ------lloKa (r 0.70926l), graphite monochromator-- IndependentFs Dl ffractometer _---- - :1 --____-__-___-pr,*-:ill_,-__------__l::_ ____

(C) Reflnenrentof the Structur€

R = [l lFol-lFcll/ElFol 0.084 0.184 0.156 p* = {r*(lFel-lfcl)'/rwfot}f, ur=o-2(Fo) 0.095 0.140 0.143 Scale factor 1.441(6) 4. 37(3) t.l4(r) Variable pararEters 72 123 69 *Ruizite, llilliarm and Duggan(1977)i macfallite and orlentite, llooreet al. (1979)who dlscuss slgnificant Als* ln these comoounds. MOORE ET AL: STRIICTIIRES OF RI/IZITE. MACFALLITE AND ORIENTITE 177

Table 5a. Ruizite atomic coordinatest Table 5c. Orientite atomic coordinatest Atom E

tlh4 0.2s00 0.2500 0.0000 lln(l) 8 0.2500 0.0000 0.2500 Ca4 0.2054(2) 0.5000 0.2599(l) tln(2) Lx8=4 0.4549(8) 0.2500 0.2499(lI) Ca 8 0.5978(4) 0.1585(l) 0.0000 si(r) 4 0.035s(2) 0.0000 0.r513(2) 0(r) I 0.r328(4) 0.2165(6)0.1291 (3) sr(l) 4xL=2 0.1057(8) 0.2500 0.0000 0(2) 4 0.3748(6) 0.5000 0.092r(s 0(3) -0.0063(5) I 0.9833(12)0.1808(4) 0.0000 0(3) 4 o.oo00 0.2857(4 0(4) 8 0.204e(il) 0.2s00 0.2245(151 sr(2) 4 0.1042(2) 0.0000 0.3951(2) si (2) 8 0.0e70(2)0.0000 o(4) 8 0.2056(8) 0.2150(e) 0.3es4(5) 0(l ) l6 0.08r2(3) 0.2164(s) 0(5) 2 0.0000 0.0000 0.5000 0(2) 8 0.0584(4)0,0000 0(6) 4 0.3674(5) 0.0000 0.0459(5) I 0.3677 0.0000 8 0.4325 0. o(7) 4 0.4437(8) 0.0000 0.2781(71 rEstinatedstandard errors ytfer to the last diqit. rEstimated =oH(l) g(f) standard errors rcfep to the Note0(5) and =att(z) or H20. last digit, E in the Table5 series ls equi- polnt.rank. t{ote 0(4) = 4- + oHi, 0(6) :91i- and0(7) =H20. case, in retrospect because of the dominant sheet motif StMd*(OH)r(SiOa)21. Convergenceof the crystal structures is reported in Table 4, part C, where R = >llF"l - all three compounds, a set of single crystal photographs was lF.llDltF.l. Although macfallite and orientite were refined much earlier, their taken, and each spot was inspectedwith a loupe for evidenceof disappointingly high R-indices militated against any urgent twinning, intergrowth, etc. When the crystals were deemed communicationof the results. However, no spurious or missing satisfactory, they were transferred to the Picker recs-l atomic positions could be located, and this problem was automated diffractometer. The data on macfallite and orientite attributed to crystals which probably are not in fact composedon were collected much earlier and processed on the AMDAHL one domain, but are at least two. We are encouargedin this facility at The University of Chicago. Ruizite, a more recent assessmentby a recent communication on the related mineral study, was processedon the oec vAx lll780 computer facility. sursassiteby Mellini and Merlino (1982). Scatteringcurves for Ca2*, Mn3*, Sia* and Or- were obtained Final structure information is arrangedsequentially, according from Ibers and Hamilton (1974). Anomalous dispersion to ruizite (a), macfallite (b), and orientite (c). Table 5 includes corrections were obtained from Cromer and Mann (1968)for the atomic coordinate parameters, Table 6 the thermal vibration heavier elements. Absorption correction involved careful parameters,Table 7 the bond distancesand angles,and Table 8 measurementof the crystal shape.The Gaussianintegral method (Burnham, 1966)was applied to macfallite and orientite, and the AcNosr program on the VAX facility was utilized for ruizite. Table 7a. Ruizite: bond distancesand anqles1 The individual crystal structures were solved by classical Patterson P(avw) synthesis. Since the structures were largely st ('l) unknown at the time, some difrculty was encounteredin each 2 ian-0(l) r.gosI I sl (l )-0(2a) I .604 -0(6) 2 I .946 2 -0(r) 1.626 2 -o(2) 2.195 l -0(3) 1.662 Table 5b. Macfallite atomic coordinatest average 2.017 aveEge 1.630

angle (des.) *2 6121-s151(r") 272 Mn(l)* 0.0000 0.0000 0,0000 1.80(6) 8t.7 t o{21(")-0,r, 2.s3 ror.6 Mn(2) 2 0.5000 0.0000 0.0000 2.36(4) 2 0(r)-0(5) 89.8 2 0(r)-0(3) 2.65 107.2 Mn(3) 2 0.0000 0,5000 0.0000 2.29(4) z o1t1-0151(") 2.73 90.2 t o1t1-0111(') 2.6't no.6 2 0(l )-0(2) 2.85 z o111-0121(') 2.72 il4.7 ca(l ) 2 0.6817(4) 0.2500 0.7954(s) 2.85(6) ca(2) z 0.3128(4) z o1r;-0121(")2.97 92.3 0.2500 0.6687(5) 2.e3(5) average 2.65 I 09.4 2 0(2)-0(5) 98.2 si(l) 0.8r07(5) 0.2500 0.1e05(6 ) 1.7e(7) si (2) 0(l) 0.6519(13)0.2s00 0.0560(I s) 1.e8(t8) average 90.0 0(2) 0.e045(ls) 0.2500 0.0778(I 6) 2.63(221 r si(2)-0(s) 1.590 0(5) 0.8387(9) 0.0332(14) 0.305n(l0) 2.25(r3) 2 -0(41 1.614 I ca-o(7)(a) -0(3) si(2) 0.I e56(s) 0.2s00 0.2e29(6) 1.76(7) 2.386 l 1.630 0(3 0.r234(14)0.2500 0.4279(14) 2 -o(4) 2.393 2.l 7(l8) average 1.612 0(4 0.3648(r3 ) 0.2500 0.3986(14)?.r0(r 7) 2 -0(r) 2.428 0(7 0.l 635(9) 0.028s(14) 0.18s8(10)2.2r(r3) r -o(2) 2.558 -0131(') si(3) 0.5029(s) 0.2500 0.3377(5) 1.82(7) I 2.624 l 0(3)-0(5) 2.57 105.7 0(s) 0.6394(I 3) 0.2500 0.5173(ls)l .ee(r7) 2 0(4)-0(5) 2.63 110.3 0(8) 0.5010(e) 0.02re(l3) 0.2426110\ average 2,459 2.0e(lr) t o1l1-01a1(") 2.6s llo.G 2 3795 0.2500 lsl 2.2 2 0(3)-0(4) 2.66 roe.e 2 0.2500 r5) 2.r 2.53 2 2500 16) 2.5 109.5 rEstlmted standarderrors rpfer to the last dlqit. standird errors are wlthin O.OlI to" o-0.; 0.000A for Ca-.oand Si-O; and 0.005A for Hn-{i 0.3o for angles. Theequivalent positions *Reflnedto 0.61(2)thr* + (referred to Table5a) are designatedas supeEcrlpts and are'(a)- = O; 0.39 Al3+occupancy. (1) . -x, -y, -z| -yt rihs+-th!+ '-' t N (21 " x, t. shar;d ea;;s. l7E MOORE ET AL: STRIJCTURES OF RUIZITE, MACFALLITE AND ORIENTITE

Table 7b. Macfallite: bond distancesand anglest

iln(t) iln(2) Mn(3) ',r.e4 2 r,|n(l)-0(7) I.9I A 2 un(2)-0H(l) l 9l 2 Mn(3)-0H(2) 2 -0H(3) I .98 2 -0(l) 2.|'l 2 -0(5) r.e4 2 -0(21 z.uo 2 -o(8) 2,18 2 -0(3) 2.21 avera9e 1.97 avera9e 2,07 average 2.03

anqle (aes.) *2 o(2)-0H(3) 2.64 8l.5 *2 0(r)-oH(l) 2.61 80.8 2 0(5)-0H(2) 2.6e 88.0 2 o(7)-0H(3) 2.73 89.2 2 o(8)-oH(l)(I) 2.88 89.4 *2 0(3)-0H(2) 2.79 84.1 ) 2 o(7)-oH(3)(r 2.77 90.8 2 0(8)-0H(',r) 2.91 90.5 2 o(6)-oH(2)(r) 2.7s sz.o 2 0(z)-6171(t) 2.79 89.3 2 0(r)-0(8) ?.99 88.6 a o(s)-o(o)(') z.s6 BG.6 2 0(2)-0(7) 2.82 90,7 2 o(l)-oH(1)(r) 3.05 99.2 2 0(3)-0(6) 3.03 93.4 (r 2 0(2)-0H(3)) 3.06 98.5 e 0111-e1s1(t) 3.07 9l.4 z o(s)-oH(z)(') s.og e5.s average 2.80 90.0 avera9e 2,92 90.0 av€rage 2.88 90.0

sl(r) si(2) si(3) r si(1)-0(2) r.62 2 si(2)-0(7) 1.6? 2 si(3)-0(e) r .63 'r 'r.66 2 -0(6) I.64 -o(3) l .63 r -o(5) l -0(r) r.65 r -0(4) l.6s r -o(4) r.6e average 1.64 average 1.63 average 1.65

'103.5 r 0(l)-0(2) 2.52 lol.l l o(3)-o(4) 2.58 1 0(4)-o(s) 2.63 103.5 't r o(o)-o(o)(') 2.64 tol,z 2 o(4)-o(7) 2.63 06.9 2 0(5)-0(8) 2.68 10e.3 'r 2 0(2)-0(6) 2,71 112.6 o(21-9171(') 2.70 112.7 2 o(4)-o(8) 2.69 108.3 2 0(1)-0(5) 2.72 1',11.7 2 0(3)-0(7) 2.71 113.0 I o(8)-o(s)(') 2.78 117.3 average 2,67 109.5 average ?.66 109.3 average 2.69 109.3

ca(l) ca(2) z ca(r)-o(7)(') z.zs I ca(2)-0H(l) 2,28 (') z -01e1 2.4s l -0(3) 2.34 l -0(1) 2.46 z -0151(r) 2.38 (') r -0(5) 2.46 2 -01s1 2.4s I -0(2) 2.74 l -o(4) 2.66 average 2.44 average 2.41

tEstlmated standard errors are wlthln o.o4 I ror 04- and Ca-{l 0.03 I tor l4n4 and si-{i 0.9' for ang1es. The equivalent positions (referr€d to Table 5b) are designatedas superscripts and are (1) =-x' -y, -zi (2) = x'l'y, z; (3) = -x, l'ry, -2. ';i1n r+-4,6s+ shar€d edges. the structure factors.3 It should be noted that the anisotropic ing block. They differ in the nature of the intersheet thermal parameters for these crystals are more likely material. The bond distance averagesfor Mn3*-O in the manifestationsof intergrowths and domain disorder, rather than f.b.b. are Mn-O : 2.02 for ruizite, Mn(lFO = 1.97 and descriptionsof true thermal motions. Mn(3)-O = 2.03for macfalliteand Mn(l)-O = 2.024 for The Mn(l!-O distancein macfallite is unusually Discussionof the structures orientite. short, but this is evidently the site where substantialAl3+ All threestructures-ruizite, macfallite, and orientite- is sequestered according to Table 5b. The intersheet arebased on the [Mn]+(oH)2(sio4)21fundamental build- larger cations are particularly interesting. The Ca-O averages for seven coordination are Ca-O^ : 2.46 in 3 To obtain copies of Tables 6a, 6b, 6c, 8, and Fi8ures 4, 5b, = 2.44 and Ca(2)-O = 2'4lA in macfal- 5d, 6b, 6d and 6f, order Document AM-85-251from the Business ruizite, Ca(lFO = is no evidence Ofrce, Mineralogical Society of America, 2000Florida Avenue, lite, and Ca-O 2.45Ain orientite.There N.W., Washington,D. C. 20009.Please remit $5.00in advance of significant substitution at the Ca sites in these struc- for the microfiche. tures. The Ca-O ranges are from about 2.3 to 2.7A, and MOORE ET AL: STRUCTURES OF RT]IZITE, MACFALLITE AND ORIENTITE t79

Table 7c. Orientite: bond distancesand anglest

iln(l ) t4n(Z ) si(2) 2 r,h(l)-0(l) r.eti 2 Mn(2)-o(3)(8) 2.04 r si(2)-0(2) I .51 2 -oH(l IOf, ) 2 -0H(21 2.09 2 -0(l) 1.63 z -oQlG) 'l 2.20 r -0(4) 2.27 l -0(3) .66 average I -0(4)(") 2.27 2.02 average 1.63 , 1"

anqle (ais.) 2 0{(l)-o(1) qol 2.71 *1 613y(.)-9131("")2.65 I 0(2)-0(3) 2.5s 102.6 2 oH(l)-o(l)(ro) 2.76 91.0 z 0131(')-61a1('u)2.77 t 0111-9111(z)z.6s t08.7 *2 sH111-q121(.) 2.77 83.4 r oH(2)-oH(2)(+) 2.81 2 0(r)-0(3) 2.67 108.7 z o1r1-e121(") 2.84 87.3 2 o(4)-oH(2) 2.85 2 0(r)-0(2) 2.71 113.e 2 o(l)-o(?)(r) 2.98 92.7 2 o(3)(6)-oH(2) 3.10 average 2.66 109,4 2 orlt1-e121(a) 3.tI YO,O 2 o(3)(a)-o(4) 3.31 average 2.86 90.0 2 o{+1('")-ot,t, 3.31 1 sl(l)-Mn(2)(a)2.os average 3.01 I ca-si(z) 3.24

si(r) Ca 2 si(l)-o(4) 't.64 2 ca-o(l)(a) z-3d -0(3) (") 2 I .73 z -01+1 2.43 average I .68 1 -0H(2) 2.43 r -o(2) 2.49 r -o(3) *1 s13;-s131(,) 2.65 100.0 averag€ 2.45 r o1e1-e1a;(") 2,75 113.5 4 0(3)-0(4) 2.77 il0.7 av6rage 2.75 109.4 'Estlnated standarderrors are within_0.04.4for H'and ca-{; 0.03 A for Mn-oand si{; 0.9" for anqles. The equlvalentposltions (referred to Table = 5c) aesignit"a'is'--- - superscriptsand are (a) = *"0-tr,'iil'l'li,'-r',""-r, (2) x, y, -zi (3) = x,r-y, -zi @l = a,'y-y,;:-""e *itl3++h3+ shared edges. t*lh2+{ir+ shared edges (dlsorder).

the Cafi polyhedron No. 23 appearsto be a characteristic Ca to six. In the second schemeMn(2) is fully occupied feature in this family of structures. but Si(l) is empty. A charge-balancedexample would be Macfallite and orientite possess additional interlayer Ca2Mn2+1OH)2tMnt+(OH)2(SiO4)21.Orientite would rep- Mn(2) in their structures. Their respective averagesare resent compositions somewhere along the join between Mn(2)-O : 2.07 and 2.13A. Both compoundsare inter- thesetwo end-membercompositions. Moore et al. (1979) pretedas possessinga (Mn2+,Mn3*) solid solutionat this suggested carMn2*Mnl+(oH)4(si3oro)-ca2Mna+(oH)2 site, but additional Mg2* may also play a major role as, (Si3ord ' 2H2Ofor the seriesat a time when the structure for example, in ardennite, which relates to orientite; and was not known. Interestingly,Mellini and Merlino (1982) sursassite,which is nearly isostructural with macfallite. proposed a model where [SiOa] tetrahedra alternate with This implies that a complex coupled relationship may [Si3olo] tetrahedraacross the fundamentalbuilding block exist between02*, OH- and possiblyH2O amongsome and this would appearto be the best compromisebetween of the coordinating anions about Mn(2). the two extremes. In orientite, the Mn(2) site is evidently half-occupied This hypothesis appears to bring several observations since the Mn(2)-Si(l) : 2.054 distance is unusually into account. The first is the presenceof [SLOrr(OH)rl short. This would suggestthat an averageoftwo ordering tetramersin ruizite, where on the averagetwo out of four schemesis being observed.In the first scheme,consider equivalent oxygens are replaced by hydroxyl groups to the absenceof Mn(2). Then the orientite structure formu- balance charge. In orientite, two out of four equivalent la would be Ca2Mn32*(OH)2(Si3Oro).Here, OH(2) is also oxygens likewise appear to be replaced by hydroxyls. eliminated, which would reduce the coordination about The second problem concerns the formula unit contents 180 MOORE ET AL: STRUCTTJRESOF RUIZITE, MACFALLITE AND ORIENTITE

Table 9. Orientite and ruizite: electrostatic valence balance of a single crystal of orientite end-member has yet to be cations and anionst investigated. Since hydrogen atoms could not be located in this ORIEMITE latter Coordinatlngcations study, we have selected ruizite and orientite, the Table 9. From these Anions ca lln(l) tln(2) sr(l) sl(2) p0 conclusion with and without Mn(2), to construct electrostatic balance calculations, crude suggestionscan o(r) , t l.7s 02- \, which oxygens are hydroxylated. In both o(21 , l. t -- \, 2.2e 02- be made on A o(3) , -- t ? 2.2e 02' instances,these involve O(4) which plays a similar role in |0(4) ?.\ -- t -- 1.57 02- both structures. It is an apical or terminal silicate oxygen 0(5) t *'t 1.00 0H- which also bonds to 2Ca + 2Mn(2) or 2Ca + lSi(l) for +, -- HzO 0(6) 0.29 orientite,depending on the absenceor presenceofbond- 0(l) 4 t- I I .79 02- ed silicon. In the former case,we elect O(4) = OH-, in 0(2) , t.? 2.29 02- the latter O(4) : O2-. For ruizite, O(4) bonds to lCa * -t | 02- B o(3) , t 1 .62 lSi(2) and we have chosen O(a) = VIOIJ.- + t/zO2- to *o(4) \ +, t.t 0.9'l 0H- 0(s) t -t 1.00 ofl- balance charge. 0.62 Hz0 A twin model was employed to explain the frequent - cmposition Caro(Hro)r{l,hr+(0H)rfsl30rol}.0(4) = 9u appearanceof bermanite crystals that satisfy X-ray ex- cmposition ca2l'h,+(Hro)2{l{ni+(0H)r[(si04)'(oH)']].o(4) = 0H- tinctions compatible with space group C2221.Kampf and Moore (1976)refined this structure in spacegroup P2r on an untwinned crystal recovered only with considerable RUIZITE dfficulty. Does orientite enjoy the samekind of relation- Coordlnatlhgstlons ship? Although there are many subgroups of Bbmm, Anions iln si(I) si(2) Po Concl usl on Pnmm, the space group found for ardennite by Donnay 0(!) 4 t t l.7e 02' and Allmann (1968),is one of them. We haveconstructed 0(21 a z.z t - 2.2e 0z- a model for space grotp Pnmm based on the Bbmm 0(3) 1 t t 2.2s 02- orientation, which admits both Mn(2) and Si(l) in the *0(4) 4 -- t 1-29 luq' in Figure 7' It features 0(s) -- \+t 2.00 02- structure without steric hindrance o(6) t -t 1.oo 0H- both tSi(2)Si(l)S(2)d0l clustersand [Si(2)Mn(2)S(2)fi0] 0(7) , Hz0 clusters. The cell contents for the two domains could be cmposi ti on cae(Hz0) z {ilnl-(0H), [si 40r I (0H) 2] ]. o(4)= oHrq-. 4Ca2Z(H2O)2{Mnt*(OH)2tSi3Or0l}with o(4) : 02- and with o(4) : rEntries include Paulinq bondstrenqths obtalned by divldlno foml charqe 4Ca2Mn2+(H2O)dMnl*(OH)2(SiO4)2(OH)zll by coordinatlonnmber lc.N. for caz*.7, ttn2*6,-tine* o,Str* 4). sinie OH- respectively.From this evidence,we suspectour hydrcgenatms Fre not detemined in the structures, "conclusion" was guidedby bondstrength sm as bonddistance deviations rere not Iistrd. crystal is an intergrowth of both domains and it is not known if pure single-domaincrystals exist. Therefore, the of orientite. Earlier studies met with problems accommo- Bbmm spacegroup for orientite is probably an averaged dating the high water content proposed in chemical model. Finally, a related cell formula can be written for analyses.Finally, the hypothesis of Mellini and Merlino ruizite. It is 2caz(H2o)2{Mn;*(oH)2 [si4oil (oH)r]] '/z) (1982) on the proposed structure for orientite and its with O(4) : OI1.-rn + O?8.The O(5) position at (0 0 in relation to ardenniteis substantiated,bearing in mind that ruizite possessesa U22 parameter which is about one

-l [-1- . si(z)oo .si{z)oo x Mn(21.25,-,25 oSi(1)00

- -ot/a u6- -

o Si(l) 50 x Mn(2)25,- 25 r Si(2) 50 o Si(2)50 oSi(2)50 . Si(2)50 x Mn(2125.:25 r Si(l)s0

.Si(l)00 x Mi12)25'- 25 .Si(2)00 .Si{2)0n L I

Fig. 7. The S(l), S(2) and Mn(2) atoms in orientite projecteddown the c-axisof the unit cell. The Si positions are denotedby dots and Mn by crosses.A possiblesite population schemewhich is sterically permissibleis underlinedand involves Si(l) and Mn(2). The subgroupwhich obtains is Pnmm, some of whose symmetry elementsare shown. MOORE ET AL: STRUCTT]RES OF RUI4ITE, MACFALLITE AND )RIENTITE

order of magnitude larger than for the other oxygens, Galli, E. and Alberti, A. (1969) On the crystal structure of againsuggesting disorder. pumpellyite. Acta Crystallographica,B25, 2276-2281. In all these structures, the fundamental building block Gottardi, G. (1965)Die Kristallstruktur von Pumpellyit. Tscher- [Mnt*!(OH)z(TOq)) doesnot seemto be disturbed,but maks Mineralogische und PetrographischeMitteilungen, 10, the difficultiesarise in the interlayermaterial. Therefore, l l5-t 19. we suspectthat the concept of the fundamental building Harrison, F. W. and Brindley, G. W. (1957)The crystal structure of chloritoid. Acta Crystallographica, -82. block is a key to relating these structures and that 10, 77 Ibers, J. A. and Hamilton, W. C. (1974)International Tables for problems of domain structure, twinning and disorder of X-ray Crystallography, 4, The Kynoch Press, Birmingham, anionic units occur within the interlayer region. Of all England, 99-100. three structure types, not one refined as anticipated for Kampf, A. R. and Moore, P. B. (1976)The crysral structure of such compounds of intermediate atomic number and we bermanite, a hydrated manganesephosphate. American Min- suspecteach of them involves somedegree of disorder. eralogist, 61, 124l-1248. Mellini, M. (1982) Acknowledgments and Merlino, S. Order-disorderin sursassite. Abstractsof Papers,13th General Meeting, IMA '82 (Varna, Messrs.Russell P. MacFa.lland Carlton W. Gutmanwere Bulgaria),p. 373. especiallyhelpful in roundingup more specimensfrom the Moore, P. B. (1981) Complex crystal structures related to dumpsof the Lake Manganesearea. p.B.M. acknowledges glaserite, K:Na(SOr)z: evidence for very dense packings supportfrom NSF grant EAR8I-21193and J.S. appreciates among oxysalts. Bulletin de la Soci6t6franEaise de Min6ralo- supportfrom the Ministry of Education,people,s Republic of gie et de Cristallographie, 104, 536-547. China. Moore, P. B. Ito, J. and Steele,I. M. (1979)MacFallite and orientite: calcium manganese(III) silicatesfrom upper Mich! References gan. Mineralogical Magazine, 43, 325-311. Allmann,R. and Donnay,G. (1973)The crystalstructure of Rumanova, I. M. and Skipetrova, T. I. (1959) The crystal julgoldite.Mineralogical Magazine, 39, 27 l-ZBl. structure of lawsonite. Doklady Akademia Nauk S.S.S.R., Britton,D. andDunitz, J. D. (1973)A completecaralogue of 124,324-327. polyhedrawith eight or fewer vertices.Acta Crystallogra- Sun, M.-S. and Weber,R. H. (1958)Santafeite, a new hydrared phica,A29, 362-371. vanadatefrom New Mexico. American Mineralogist, 43,677- Burnham,C. W. (1966)Computation of absorptioncorrections, 687. andthe significanceof the endefect. AmericanMineralogist, Williams, S. A. and Duggan, M. (1977)Ruizite, a new silicate 5l, rs9-167. mineral from Christmas, Aizona. MineralogicalM agazine,41, Cromer,D. T. andMann, J. B. (1968)X-ray scattering factors 429-432. computedfrom numericalHartree-Fock wave-functions. Acta Crystallographica,A24, 321-324. Donnay,G. andAllmann, R. (196E)Si3O1e groups in thecrystal Manuscript received, May 12, 1983; structureof ardennite.Acta Crystallographica,B24, g45-g55. acceptedfor publication,August 22, 1984.