American Mineralogist, Volume 61, pages 88-94, 1976

Painite, CaZrBlLlrO,rl: Its crystalstructure and relationto jeremejevite,Bu[[rAl6(OH)sO1r], and fluoborite, Br[Mgr(F, OH)rOr]

Plur- BRre,uMooRE r.No TnreHnnu AnerI Department of the Geophysical Sciences, The Uniuersity of Chicago Chicago, Illinois 60637

Abstract

Painite-CazrB[Al,O,s], hexagonalP6s, a :8.715(2), c : 8.472(2)A,Z : 2-possessesa rigid and dense [AlrO,r]'- octahedralframework, topologically identical to those found in jeremejevite, B'[IBAI6(OH)aO,,] and fluoborite, B,[Mg,(F,OH),O,]. R : 0.071 for l6l8 independent reflections. The octahedralframework is linked to [BOr]3 trianglesand [ZrOu]8-trigonal prismsatlf z and a largepipe at 0 0 z is cloggedwith compressed[CaO"]'0- octahedra. Average interatomic distancesareCa-O=2.398,2r-O:2.126,8-O:1.380,A1(l)-O: l.9l5,Al(2)-O: 1.918, and Al(3)-O : l.9l4A. The octahedral framework in painite, resistantto attack by acids and bases,suggests a highly refractoryphase and the possibilityof other equally resistantcompounds, hypothetical examplesbeing NaNbs+B[Alrors] and llUutB[Al"O,"]. ln the latter, thepipewould be lree from obstructions.

Introduction Three-dimensionalsingle-crystal X-ray diffraction intensitiesabout the a2-rotation axis were collected Painite is a curious species,first reported on a PnILnrn semi-automateddiffractometer with by Claringbull, Hey and Payne(1957) from the graphite monochromatized MoKa, (tr : 0.70926A) minesof , Burma. It was found as a -red radiation. With 2d-^* : 69.5", data were gathered 1.7 gram singlehexagonal crystal of hardness8. They through the k -- 0- to ll-levels. Other salientdetails: proposeda formula Ca,SiBALoOr.,the slight imbal- scanspeed lomin t, aperture2.0",20 secondback- ance in charge due either to non-integral or ground measurements,half-scan range of 2.0owiden- total cations. ing to 2.5" at higher levels.Reflection pairs of the We continue to expressinterest in dense oxide type l(hkl) and l(hkl) were collected.An absorption structures,especially those of the aluminates.In addi- correction was applied to the crystal using u : 22.8 tion, a structural relationship was suggestedin the cm 1, approximating the shapeof the chip by select- crystal cell data for jeremejevite, AI6(OH)r(BOr)u. ing seven facets, we employed the Gaussian in- Our findings reveal an elegantstructure for painite, tegration method, described by Burnham (1966). the aluminate framework of which is related to jere- This correction was small since maximum difference mejeviteand to the octahedralframework of fluobo- in transmission factors was about 57r. Additional rite, Mg'(F,OH)B(BO3).Finally, we demonstratethat correctionswere made for Lorentz and polarization the correct formula for painite is CaZrB[AIrO,r]. effects. Weights applied to the processedreflections included an uncertainty for the z-angle maximum Experimental mis-settingof 0.lo, tilting error of 0.05o, average A thin sawn plate of the type crystal (B.M. 1954, crystal size error of 0.008 mm, and the counting 192) irom near Ohngaing village, Mogok, upper statistics.Two setsof Fo were available:those which Burma, was kindly provided by Mr. PeterEmbrey of were based on an average of F(hkl) and F(hkl) (cen- the British Museum of Natural History. The chip trosymmetric case) and separate F(hkl) and F(hkl) selectedfor structure analysis was a flat fragment, (noncentrosymmetriccase). measuring0.31 X 0.22 X 0.10mm alonga,,a\, andc, During the analysis,it was neces- respectively.Calibrated precessionphotographs es- sary to challengethe chemicalcomposition of painite tablished the cell data in Table l. proposed by Claringbull et al (1957), and we sub-

88 PAINITE,' CRYSTAL STRUCTURE AND RELATION TO JEREMEJEVITE AND FLUOBORITE mitted a fragment to electron probe analysis,per- TlsI-r [. Crystal Cell Parameters for Painite, formed by Dr. L M. Steele. The crystal was Fluoborite, and Jeremejevite* homogeneousthroughout and revealedmajor Ca,Zr, Painite Fluoborite Jerenejevite and Al with all other elements of atomic number B.irs(2) s.o6 greaterthan Na not detected.The standardsselected "tAl c(I) 8.4?2(2) 3.06 8 l8 were diopside (Ca), synthetic ZrO"(Zr), and corun- 222 2 space grcup P6g P63/n P6sln (?) dum (Al). Correction of the data utilizedthe AnpnN-z program of Hadidiacos, Finger, and Boyd (1969). fomula uit CaZrAleolslBOtl Me3(F,oH)rImr] Ar5 (oH)3 [Bo3] s

The resultsin Table 2 depart seriouslyfrdm the origi- axial ratios o.97O (c/a) 1 0r3 (3cla) 0 9S5 (c/a) nal chemicalanalysis, with poor agreementfor all the specific gravityr 4.01 Z.ag 3.28 elements reported. We suspect that ZrO2 (not re- density, m cn-r 4.01 2.82 3-24 ported in the earlierstudy) was in part coprecipitated Cell paraneters for fluoborite fron Takeuchi (1950) and for jerenejevite fron with CaO and AlrOr, and in part reported as the bolovastlKov eE aL. I 1955t . rclaringbull contribution to SiO, which we found to be absentin et a7,. (1957), for painite The data for fluoborite ancl jerenejev- ite are fron Geijei md Dmour respectively, quoted in Palache et al, (195I). the crystal(< 0.01%).Although we couldnot analyze boron, the structure analysis clearly revealed the presence of fully occupied [BOJ'- triangles. The convergedto R : 0.16 and did not reduce further, probe analysisis in satisfactoryagreement with the despitea rather sharp and cleanelectron density map. proposed formula CaZrBAlrO,r, which yields p : We noted,however, that the Alt+ temperaturefactors 4.01 gm cm-3, in excellentagreement with the specific were unexpectedlylarge (1.5 to 3.04-') and decided gravity of 4.01 reported by Claringbull et al (1957). that the structure was in fact noncentrosymmetric, based on spacegroup P6s, and that the actual struc- Structure analysis and refinement ture departed only slightly from centrosymmetry. One of the reasonswe investigatedpainite was due Since correlations in parameters were high, two to an apparent relationship with jeremejevite, blocked matrices were refined in alternate sequence. A16(0H)a(BOr)u.Golovastikov, Belova, and Belov We also concludedthat the formula unit was in fact (1955), who approximately determined the crystal CaZrBAlrO* and substitutedthe scatteringcurve for structure,established that for jeremejevite,Z : 2, a Zr in place of Ca at "Ca(2)". This conclusion was : 8.56,c : 8.18A, spacegroup P6r/m. We proposed forced on the basis of site multiplicity refinement and that painite and jeremejevitepossessed similar struc- inspection of interatomic distances.The parameters tures and that Al3+ in the former isomorphically re- refined smoothly until R became0.071 for all 1618 placed some of the B3+ in the latter compound. A non-equivalent reflections, including F(hkl) and three-dimensionalPatterson synthesisP(zuw), sup- F(hkl) pairs. Inversion of the atomic coordinatesdid ported the isomorphism for the octahedralAl'+ and not materially affect the reliability index and it was the anion frame, but the remaining cations were not not possibleto selectunambiguously the proper polar clearly deciphered. orientation of the structure.This study provides yet The N(z) test on special reflections(see Howells, another examplefor which a crystal structure analy- Phillips, and Rogers, 1950)and the P(y) test on gen- eral reflections(see Srikrishnan and Parthasarathy, TnsI-n 2. Chemical Composition 1970)supported the centric group P6"/m. A trial p- of Painite synthesis (Ramachandran and Srinivasan, 1970). 1 yielded unexpectedresults: no isomorphism between 83+ and Al3+ was noted and, in addition, a strong CaO 7.L7 r5.7 8.33 A1203 69.02 76.2 68.19 densityappeared at and a weaker densityat 000. 3 +* Bzos n.d, ) ) < 17 We tentativelyascribed Ca(l) 0 0 0; Ca(2)3tt Al(l)* ZrO2 t8.77 n.d. 18.31 0 l and Al(2) + + 0.09. The anion frame agreedwell Si02 absent 5.6 with the jeremejevitemodel. Further B'-synthesesled Hzo n.d. 0.7 : to R 0.33, and at this stage it was apparent that 94.96 100.4 r00.00 "Ca(2)" was some other more dense ionic species. IElectron probe analysis, this study (I. Allowing its occupancyto vary, a trial least-sqpares M. SteeIe, analyst), refinement led to R : 0.17, whereupon B3+ was 2claringbult et a7., (L957). 3conputed unambiguously located at * ? *. Further refinement for CaZrB[A190ts]. P. B. MOORE AND T. ARAKI

Tlnu 3. Painite.Atomic Coordinatesand curves for Ca'+, Ztn+, Al3+,Bo, and 01- derive from Isotropic Thermal Vibration Parameters* Cromer and Mann (1968), and the anomalous dis- persion corrections for Ca, Zr and Al from Cromer B(i2) and Liberman (1970).The secondaryextinction cor- rection (Zachariasen, 1968) converged to co : 3.0(3) ZT 2/3 I 17 tl4 0.s7(1) X 10-6 and the scalefactor, s : 6.31(a)where Fo : 0 0 0 .492e(2) 1.23(2) JF". A1(1) 0.3329 (1) 0.5373(r) . 74e0(3) .6r(2) The polar nature of the structure must be accepted A1(2) .342s(2) .362s(2) .07e1(1) .63(2) as fact and obtains from slight deviations of the Ar (3) .3437(2) . 3s96(2) .4224(r) .s4(2) [AleOrE]e- framework from centrosymmetry. Golo- B 1/3 .24es(4) .84(8) vastikov et al. (1955) proposed the centric group, 0(1) . 3992(3) .ssrs (3) .249s(4) .81(3) P6"/m, for the structurally related jeremejevite, but refinementare crude. We suspectthat 0 (3) .40s2(3) .s237(3) . sele (5) .6e(4) their data and o (4) .4060(4) .s23s(4) . e070(3) .s4 (3) a more precise refinement of the jeremejevite struc- ture will revealthe spacegroup P6r; this is supported 0(2) . 328r(3) . 2r86(3) . 2s03(s ) .6e(3) 0(s) . 30le(3) . 193s(4) .s807(3) . s8(3) by a positive piezoelectric test reported in Palache, o (6) .2s83(4) .rer2(4) .9r6s(3) .73 (4) Berman, and Frondel (1951) obtained by the os- Estinated standard errors refer to the last digit. cilloscopemethod on a sawn plate. The atomic coordinatesand isotropic thermal vi- sisestablishes the correct formula, and it is gratifying bration parametersappear in Table 3, and Table 4 to note that the electronprobe analysissupports our lists the structurefactor data.1Owing to high correla- deducedformula. The lessonto be learnedis that no tions, we did not attempt an anisotropic thermal wet chemical analysis should be trusted in the ab- vibration parameter refinement. senceof some thorough qualitative results such as Description of the structure can be obtained from an emissionspectrogram. Programs used in this study included a locally Painite possessesa rather elegant and aesthetically modified version of the familiar Onrls program of pleasing structure which can be directly compared Busing, Martin, and Levy (1962). It has options for with the octahedral framework structure of fluobo- varying the proportionate contribution of two scat- rite, Mgr(F, OH)s(BOs).Fluoborite was investigated tering curves at any site, multiple blocked by Tak6uchi (1950) who establishedits structural refinements,retrieval of bond distancesat any stage motif. lt is based on a framework of corner-linked and options for B- and 7'-syntheses.The scattering octahedral edge-sharingbands, two octahedra in width, which run parallel to the c axis. The corner links relate symmetry-equivalentbands by the 3-fold rotation at tr3 z and 0 0 z. The resulting framework has composition [Mgr(F,OH)sos]'-. Since three oc- tahedralcenters coordinate to eachanion. the ratio of octahedralpopulations to anionsis exactly 1:2.Open hexagonalchannels at the origin prompted the term "pipe structure" by Tak6uchi (1950); and Moore (1972), and Moore and Araki (1974) have exploited the octahedraledge distance as an exampleof a wall- paper-typestructure. This term appearsnatural since the c-axial repeat is not only parallel to octahedral edgesbut is itself the octahedraledge distance. Thus, no nonequivalent atoms overlap in this projection. The [BOr] trianglesare orientedperpendicular to the trigonal axesand completethe structure,an idealized diagram of which appearsin Figure l.

Frc. I ldealized fluoborite structure projected on the regular 'For a copy of the structure factor data, Table 4, order triangular net {3,6}.The MgOr(F,OH )r octahedra are ruled and the DocumentAM-75-010-B from the BusinessOffice, Mineralogical [BOr] triangles are stippled. Note the missing anion at the origin Society of America, 1909 K Street, N.W. 20006. Please and the resulting large pipelike channel. remitin advance$1.00 for the microfiche. PAINITE: CRYSTAL STRUCTURE AND RELATION TO JEREMEJEVITE AND FLUOBORITE 9l

Painite possessesthe identical framework topology triangles.The assembledpainite structureis featured with formula [AlrO.]3-. The c-axial repeat,however, in Figure 2. is three times that of fluoborite (Table I ), a Perhaps even more remarkable is a curious consequenceof ,a rather remarkable ordering of the structural relationship between fluoborite and remaining cationic species.The structural differences jeremejevite, A16(0H)3(BOs)3(BO3),.As in painite, can be discernedat the positions0 0 z andllz with the c-axial repeatis trebled that of fluoborite (Table I ) respectto the painite cell. At 0 0 z, the sitesare all and all three structureshave 36 anions in the painite- empty in fluoborite but in painitethey are occupiedat shaped cell. The jeremejevitestructure parameters, z - 0 and * by Ca'z+cations in compressedoctahedral obtained from Golovastikov et al (1955), were in- coordination by the O(5) and 0(6) framework oxy- verted to establishthe sameorientation of anions as gens.At I t z, fluoborite has 83+ populations at z : $, those of fluoborite and painite.The framework com- #, and l$ with respectto the painite cell. Painite has position is [trAldOH)Ou], where [ : vacancy,and a B3+cation at z : # and in addition Zra, atg,the it is seen in Figure 3 that only two-thirds of the latter cation in trigonal prismatic coordination with octahedraare occupiedalong the columns such that respectto the O(3) and O(4) framework oxygensat g every third framework position along c is empty. As and iA.Thus, Zra+ achievesthe role of the two 83+-O in fluoborite, the sitesat 0 0 z are empty but the sites

t--_

i*\ \z I t,' 5 /'- \ I '. 1 |F*- \A

Ftc 2. Polyhedral diagram of the painite structure showing symmetry elements, the [AlrO,r]"- framework (ruled) and the [BOr] triangles at z : I. The Zr-O bonds at z : I are drawn as solid lines and the Ca-O bonds as dot-dash lines. The Be+and Zra+ oositions at z = | are not shown. The loci of the atoms correspond to the coordinates in Table 3. 92 P, B. MOORE AND T. ARAKI

+tt4 I

f f

t Frc. 3. A section of the jeremejevite structure showing symmetry elements and polyhedral projections. The B(2)O, triangles are stippled and the B(l)-O bonds are drawn bold This diagram can be directly compared with Figure 2. The coordinates were obtained from Golovastikov et al (1955) and inverted so that a direct correspondenceto fluoborite and painite can be recognized.

at|4 z have 83+populations at # and 41.Most curious chiometry obtains and exploitscations of two distinct of all is the additional corner-linksof [BOr] triangles charges,Mg'+ and A13+.Along the 3-fold axes,dis- at x y fz1.i y, f2,etc, between the empty octahedral crete ordering schemes are encountered. One struc- positions in the framework. These [BOr] triangles ture, jeremejevite,exploits ordered vacanciesin the have one edgeparallel to the c axis, and theseedges octahedral framework such that only two-thirds of link the broken octahedral columns together. In ef- the sites are occupied, thus affording a new set of fect, the [BOr] triangles are situated at the outer faces positions for additional IBO3] triangles. of the empty octahedra. All this suggests that the fluoborite-type The structural relationships among fluoborite, framework is unusually adaptive and may be the painite, and jeremejevite are best compared crystal basisof yet more relatedstructure types. The kinds of chemically by adopting a more unconventional(but ordering schemesencountered in the three structures more sensible!)expression for the formulae. In these reported herein open up mind-boggling possibilities formulae, the octahedral frameworks are bracketed for other hypothetical arrangements and as follows: compositions.[t would appearthat a searchfor other exotic structures related to the fluoborite framework Fluoborite Bs [Mgr(F,OH)'O'] would proceedwith prime emphasison phaseshaving Painite CaZrB [AlrolE] the following properties: (l) P63 or Jeremejevite 85 [I3AI6(OH)sO16] - P6,/m; (2) a - 8.5-9.2A; Q) c/a ratio 0.33N, where, in jeremejevite,E : octahedral vacancy on where N : 1,2,3,. . . ; and (4) lzN anions in the cell. the (pseudo-)mirror plane. distortions The geometrically idealized arrangements of all Bond distancesand three structures belong to space group P6t/m and Painite consistsof Al(l)-O, Al(2)-O, and Al(3)-O their cellshave the samemetrical properties,provid- octahedra; a B-O triangle; a slightly compressed ing the c axis of fluoborite is trebled. In two of them Zr-O trigonal prism; and a highly compressedCa-O (fluoborite and painite) the same framework stoi- octahedron.Although the anion framework and as- PAINITE: CRYSTAL STRUCTURE AND RELATION TO JEREMEJEVITE AND FLUOBORITE 93

Tenu 5 Painite Polyhedral Interatomic Distances and Anglest

Ar(2) A1(3) Ca

Ar(1) -o(s) r.827 erlz; -o1s;" t. E34 nr1:1-o1ey" 1.854 Ca -0(6) 2.371 -0(6)i r 1.829 -0 (2) 1.880 -0(2) 1.867 -0(s) 2.425 -o(2)-- 1.909 -0 14t. 1.903 -0 r .870 rst. average 2.398 -0 (3) r.94s -oirj' 1.910 -oiai' 1.894 -0 (4) r.949 -0(6) 1.924 -0(3) 1 ; .905 tt -0(1)- 2.0s2 -0(r) 2.0s7 _0(1) 2.092 o rsl -o(61 . . . 2.683 68.0 oioi.. -oioil" J.esr 112.8 average 1,915 average 1.918 average t .914 ois1"-oisj' s.sss 1r1.0 average 3.329 89.9 H"le-4- (degrees) o(r)] -o(4) 2.4s2' 77.5 ors)t -o(+t. 2.4s0* 79.9 o1s; -o1a;' z.qso* 80.3 o(r)' -o(3) z.qs8* oirj -otsj' z.qse* 78.0 o(r) -o(4)i 2.492* 77.2 0(3) -o(s) 2.ssr' 0(4) -o(6) 2.s61' o(3) -o(s)t 85.0 84.0 2.ssr" 3 zt -o(3)i 2.126 o(4)rr-o(6) 2.s6r.' 0(r) -o(2)r 2.648' 84.4 0(2) -0(41- 2.641 89.2 3 -0 (4)^ 2.126 0(2)ii-0(4) 2.63s E6.2 0(2)..-o(3)- 2.6sr 88.7 o(r) -o(2)rr 2.648* 83.8 -o(6) 0(2)^'-o(3) 2.63E 86,4 0(s)---o(6).. 2.683 91.1 0(s) i; 2.683 92.2 average 2.126 o(3)i -o(4) 2.671*' 86.6 0 (4) -0(s) ii 2.7ss 0r2l -0r6ti: 2.740 94.9 o(r)i -0(6) 2.782 94.6 0(2) -0(s)ii 2.76s 96.2 oisi -oiei" 2.778 -- '* o(r):. -0(s) 2.821 93.9 0 (r) -0(sl 2.773 90.7 o12) -o15).. 2.808 97.4 3 0(3) -0141. 2.6?0 ll.g o(2)-"-o(6) 2.812 r99.0 0(2) -0(6) 2.839 96.5 oiri. -oioitt 2.840 89.4 s oisi -otrjll 2.860 84.5 o(s)r.-0(6) 2.815 102.2 0(1)r -0(4) 2.9rs 94.? 0(4)- -0(s) 2.907 I01.1 3 0(4) -0(4)-' 2.872 85.0 o(2)---o(sl 2.867 100.3 o(3)' -0(6) 2,s39 100.1 0(r) -0(3) 2.9t4 avefage 2 801 82.4 avefage 2,684 89.6 average 2.707 90.0 average 2,104 899

3 B -ortt. 1.3E0 : o(r)-oirit" 2.3st tEstimted standard deviations do not exceed !O.OO4f for Me-O and lO,006,& for GO'.

"shared orygen edges betveen A1, "'shared oxygen edges between Al md zr -x, i ! -y, l/2+z'' ii, = x-y, x, I/2+z; LLr = -)rr x-Ir z, and iv = y-2, -x, z applied ro coordinates in Table 3. sociatedcations are ideally centrosymmetric,the ac- appearsthat the contributions of the Ca'+-O bonds tual structure possessesslight distortions away from do not greatly affect the framework and that those P6t/m. This can be noticed in the interatomic dis- bonds are weak. The BIII-O 1.38and Zrvr-O 2.13A tances in Table 5, where Al(2) and Al(3) would be averagesare exactlythose predicted from ionic radii equivalentfor P6s/m. The individual distancesto the tables.These observations suggest that the [Alro's]'- same anions not only vary well beyond the error framework adjuststo accommodatedeviations from limits, but the order of anions (the distancesare electrostaticneutrality but in a way that is not imme- tabulated as increasingmagnitudes) is not the same. diately obvious. In many respects,the framework The distortions cannot be explained by anisotropic averagesout the distance distortions such that the bonding behavior for the cations in specialpositions ideal symmetry of P6r/m is lowered ro P6, Another along { Nz:ZrOu and BO3 possess6 symmetry within adjustment in the framework resultsfrom Al-Al re- the limit of error in coordinates. pulsions across shared edges:these are among the The real distortionsappear to be a result of serious shortestdistances for their polyhedra. deviations from electrostaticneutrality for some of An interestingaspect of the painite structureis the the anions. Table 6 presentsthe electrostaticbond strengthsums as deviations,Apx, from neutralityand TesI-r 6 Painite Electrostatic Bond Strength the relationshipof thesedeviations to those found in Sum Calculations* the Al-O bond distances.O(l) and O(2) seriously depart from local neutrality, with Apx : *0.50 and Ani-on Coordinating cations aPx AAl-O -0.50 e.s.u.respectively. Thus, the Al-O(l) average o(r) B+Ar(1)+A1(2)+Ar(3) +0.50 +0. laal distanceis 0.14A longer than the polyhedralaverage. 0(2) A1(1)+Ar(2)+Ar(3) -0.50 -0.03r The Al-O (2) averagedistance is shorter than the o(3) Zr+At(t)+A1(2)+A1(3) +0.l7 +0.004 polyhedral averagebut the differenceis not as great 0(4) Zr+A1(1)+A1(2)+Ar(3) +0.17 -0 .00r as anticipated. O(5) and 0(6), with Apx : -0.17 0 (s) Ca+A1(1)+A1(2)+A1(3) -0.17 -0.072 e.s.u.,show AAI-O between0.05 and 0.07A lessthan o (6) ca+Al(1)+A1(2)+A1(3) -0,17 -0.047 : *Apx the polyhedral average,with O(3) and O(4) (Lpx = deviations fron electrostatic neutrality (px = 2.00), AAl-o *0.17 e.s.u.)within the rangeof the averagevalue. It = deviations fron A1-{ 1.9164 averap,e. 94 P B. MOORE AND T. ARAKI large pipelike channel at 0 0 z. This is clogged by We thank Mr. PeterEmbrey for the cut plateof painite.Dr. lan M. Ca'z+which bonds to O(5) and 0(6), resulting in a Steele rewarded us with a careful electron probe analysis, the which highly compressedoctahedron. If the ideal fluoborite results of confirm the formula derived by structure analysis. It is also a pleasure to acknowledge the National ScienceFoun- framework is inspected(Fig. I ) it is seen that the dation for continued support through the NSF grant GA 40543 centerof the pipe is actually representedby a missing and through the Materials Research Laboratory grant adminis- anion position. Consequently,the pore diameter of tered to The University of Chicago. the pipe is about the same as that of an O'- anion. References Thus, cationslike Lit+, Nal+, Kr+, Mg2+,Ca2+, Sr2+, BunNueu,C. W. (1966)Computation of absorptioncorrections, and Ba2+should accommodatethemselves within the and the significanceof the end effect.Am. Mineral. Sl, 159-167. pipe. In painite, there are no other obstructions be- BusINc, W. R., K. O. MnnrrN, rNo H. A. LEvy (1962)Onrrs, a yond the Ca2+cations. In many respects,the aperture Fortran crystallographic least-squares program. U.S. Natl. in the painite framework resemblesthat in p-Alros, Tech. Inform. Seru. OnNI--rn-305. which also resultsfrom a missinganion. Like painite, Cr-enrNcnurr,G. F., M. H. Hrv, rNo C. J. P,rvNr (1957)Painite, the position may be occupiedby Ca2+,as in hibonite a new mineral from Mogok, Burma. Mineral. Mag.31,420-425. Cnonann, D. T lNo D. LrnnnvnN (1970) Los Alamos Scientific (CaAl,rO,n) , or by any of a number of alkalis,depend- Laboratory, Uniu. Cald. Rep. rr'-4403, uc-34. ing on the charge of the residualframework. -, AND J. B. M.,\NN(1968) X-ray scattering factors computed The relationshipof painite to B-AlrO3 addsinterest from numerical Hartree-Fock wave-functions.Acta Crystallogr. to its structure. An appealing feature is the one- A24,321-324. (1955) dimensionalquality of the pipe which is surrounded GoLovestxov, N. I., J. N. Brlovl, rNo N. V. BELov Crystal structure of eremeevite. Zap. Vses. Mineral. Obsches. in turn by a rigid tightly bound aluminate ( Leningrad ), 84, 405-414. framework. Such a pipe, like the sheetsof missing HADrDrAcos,C. G , L. W. FTNGER,rNo F. R. Bovo (1969)Com- anions in B-AlrOr, may provide a good medium for puter reduction of electron probe data Carnegie Inst. Wash. conduction of intermediate-sizedalkalis through a Year Book,69,294. solid crystal, even at very high temperatureswhere Hownlls, E. R , D. C. Purr-r-lps,AND D. RocERs (1950) The probability distribution of X-ray intensity. II. Experimental in- aluminosilicate structures such as the zeolites dis- vestigation on the X-ray detection of center of symmetry. Acta integrate.The existenceof a largenatural singlecrys- C rystallogr. 3, 210-21 4. tal of painite as well as its extremeresistance to acid Moonr, P. B. (1972) Wightmanite, Mg,(O)(OH),[BOs].zH,O, a and base attack ("Painite is a highly resistantmin- natural drainpipe. Nature ( Phys. Sci.), 239, 25-26. -, (1974) eral, insoluble in acids, and only slowly attacked by ANDT. Anext Pinakiolite,warwickite, and wight- manite: crystal chemistry of complex 3A wallpaper structures. fusion with sodium carbonateor with sodium pyro- Am. Mineral 59, 985-1004. sulfate"; c/Claringbull et al, 1957)suggests that the PeLecse, C., H. BsnltnN, eNo C FnoNorr- (1951) The System of structure type is not only thermochemically stable , VoL.2,7th Ed., John Wiley & Sons, New York, p. but also that the framework is that of a highly re- 330-332. (1970) fractory compound, capableof withstandingthermal Rnpr,rcseNoneN, G. N., lNo R. SrruveslN Fourier Meth- ods in Cryslallography. Wiley-lnterscience, New York, p. and chemical abuse. For these reasons,our interest 96-r19. and attention are now being drawn toward its syn- SurntsnNlN,T., nNo S. Pnntueseneruv (1970) A modifiedN(y) thesis and the synthesisof possibleanalogs such as test for centrosymmetryfor crystalscontaining heavy atoms. Z. NaNbs+B[AlrO,r] and U6+B[Alro18].The latter com- Kristallogr.131, 186-195 TextucHr, Y. (1950)The position is especially appealing since the pipelike structureoffluoborite. Acta Crystallogr. 3,208-210 channelwould be free from any obstructions.On this ZlcHenrnsrN,W. H. (1968)Experimental tests of the general note, we speculatethat the open pipe may selectively formula for the integratedintensity of a real crystalActa Crys- sieve He but not the other inert sases at hieh tallogr A24,212-214. temperature.

Acknowledgments

To sacrifice a port.ion of the only known crystal of a mineral- Manuscript receiued, May i,5, 1975; accepted and a gem at that!-is not an easyand welcometask for a curator. for publication, September 11, 1975.