American Mineralogist, Volume 58,pases 523-530, 1973 TheCrystal Structure of Tincalconite' Clnurro Gtncovtzzo, Strvto MeNcFIBrrr2, ANDFrnNeNpo Sconnlnr Istttuto di Mineralogia, Uniuersitd di Bari, Italia Abstract -+ - Tincalconite is trigonal, spacegroup R32, with hexagonalunit cell a = 7l'09 0.03, c 21.07 -+ 0.04 A and Z - g. The crystal structurewas determinedfor a syntheticcrystal by in- terpretation of a three-dimensionalsharpened Patterson synthesisand by use of the tangent method of Karle and Karle. The R index for 337 observedreflections is 0'06, and 0'07 for 398 including the non-observedones. The structure consists of discrete polyions [B,O"(OH),f':, contained in the cavities of a Na-polyhedra framework. The polyions are the same as in borax, and some structural rela- tions between tincalconite, borax, and kernite can be emphasized.The framework of Na- polyhedra is the result of three dimensional sharing of faces, edges.and corners. Introduction or an irregular arrangement.On the basis of the crystal structureproposed Tincalconite is a hydrated sodium tetraborate, above considerationsthe unlikelY. NazB+O;(OH)4'3HrO.Except for only a few oc- by Invers(1948) looked currences,natural tincalconiteis known only as a ExPerimental fine-grainedpowder (Pabst and Sawyer, 1'948), whereasartificial crystals have an octahedron-like No known natural crystals are suitable for the structural habit. Hence most propertiesof tincalconitehave study. Synthetic crystals of Na,B'O"(OH)''3H*O were borax at nearly beendetermined on syntheticcrystals (Palache et aI, easily grown from aqueous solutions of A suitable tincalconite crystal was chosenand coated 1951). Tincalconiteis closely related to borax, 80'C. with cellulose acetate to prevent, as much as possible, re- NazB+O;(OH)4'8H2O.The reversibleequilibrium hydration and conversion into borax. ? relationshipsamong tincalconite borax and the The lattice parameters were determined from the /rk0 and tincalconite,borax, and kernitewere fully explained Okl Weissenberg photographs calibrated by superimposing by Christand Garrels (1959). At normalconditions single-crystal quartz reflections. The Laue-symmetry group of relativehumidity and temperature(i.e., 60 per- determined from hkl Weissenbergphotographs is 3z' The space X-ray data are the following: cent relative humidity, 2O-25"C), tincalconiteand groups consistentwith the borax rapidly and reversiblyconvert to one another R3m:'R32;R3m (Christand Garrels, 1959). (Cuthbert and Petch, 1963a) and the The first consistentresults for the chemicalformula The Nun spectrum of the Patterson synthesis showed space group of tincalconite were inspection and the crystallographic data R32 to be the most probable. - given by Christ and Clark (1957) and Petch et al The cell dimensionsare ah = 11.09(3),cr 21.07(4) A; (1962) and later confirmed and extended in many the numbers in parenthesesrefer to the estimated standard other works (Christ and Garrels, 1959;Btay et al, deviations in terms of the last decimal place cited. Thus density 196l; Cuthbertand Petch,1963a, 1963b). According 11.09(3) indicates art esd of 0.03A. The calculated g/cm', which compares to the specific gravity of studies, the correct chemical formula is is 1.94 to these observedby Pabstand Sawyer (1948). (on 1.88 NarBnOu(OH)n'3HrOinstead of NarBnO''5HrO A total of 398 independentreflections were collected, 61 the assumptionthat tincalconite contains the same of which were below the observationallimit. The intensities polyionas borax). The spacegroup is not R3 (Minder, were measured by means of a microdensitometer from 1935)but R32 and the sodium atoms lie on special equiinclination integrated Weissenberg photographs taken (/ from 0 to 13) with Ni-filtered Cu positionssurrounded by anions in either a regular around the c axis radiation. The intensities were then corrected for Lorentz t Paper presentedat the V Congressof the "Associazione and polarization factors. The crystal used for the exposures Italiana di Cristallografia," Bari. October, 1971. had an irregular shape. No allowance was made for ex- 2Present address: Istituto di Mineralogia dell' Universiti tinction or absorption corrections;however, the latter effect di Firenze, Italia. is almost negligible becauseof the crystal's low absorption 523 524 GIACOVAZZO,MENCHETTI, AND SCORDARI coefficientp (- 24 cm-1 for CuKa) and small size malized,structure amplitudes (Table 1) were then (R-'" - = 0'02,R-"* 0'05mm)' calculatedwith scaleand temperaturefactors as ob- tained bv wilson's method, and the structure was structure Determinationand Refinemernt solved by application of the tangent formula (Karle A three-dimensionalFourier synthesisphased on and Karle, 1966). positionsobtained for the Na atomsfrom the partial In the attempt to obtain phasesfor 109 reflections resolutionof the Patterson synthesisdid not show with lEl > t, ttre reflections (461), (093) and unambiguouslythe remaining atomic positions.Nor- (330) were selected,with the first as the origin-de- Tesre l. Measured and Calculated Structure Factors hkFoFo hkFoF" hkFoFo hkFoFo aars rtxt l|'$ ttar a7$s tcttttt rFaa atn ,ao0 tl.Ft axla )nar ,ran sr.,s trtrt f{a) ,a6aa axra rri atgr ol?x alot aaats 2r, trt 1g- 7rA6 ,r9 606 fltr 77rtr! rr.t6 raraa aartl caqc trt[t .xt ,au arztl! 6Crt 72laa anfi t!rat aar2t 2UX It. lo 7 tt,rt r16tq ,.L, trt6a to t. la l2 ant o9tr aJtt? rao.la ?t9tt rll!a )yt, to tt tt a!t!? erTra 2ar{ rr!!t laar orst ,6a7 aiata ,ru ot2rd llt2l 2 rr to a!!t olataa c{4 eat6 a,|r otrtte Irtlt Floa ttt€tit 567q ratl& ' ? rt rdtl fttrv Itril at6!t a lra rrl a I it, lla 427a, 70s l!0, aattrl 1ia6 ic{a it. ra t aFrta aarn eEtl !aat ,sttta ,21 { ,a2aa atru tann oatal aaa27 )arr ttrt9 to0 otato rnu !lttrt a.tto t.tr9 an!! ao16lQ I f. l3 rt at1t3 1a7r alnr I a.ica rt9t9 rol!4 aatTtt t 2tt19 .J'J' ,7a?! atltla I o.!at 7t619 !alt tllJrti r J.arl 24at tstol ,afc ,2a2t tna! ,trrt? 0tta .Efr aaii r Io itt ot9 ttta a*it! a tat ty trrr Itrx att?!! falal 5Sat aao ?o6Q ajg rr?aa tatr Ttltr? ,r7u ax* Ftat? 70ttto !I27 29{ ttttl la.tta Ilto tatel arait ,IJtT ayt, o. tl tt c ttt lg to 0. ta It JXt titltt, l. ir t! ,ato a{rt r. 12 l2 aatft )&r? ptt, otDtt tata! ltta 7a6a5 !qa1 oaraJ o to. to io r.ts 57rn !rtr? ralQttt a9a, 9aat r. Il ltar{ ,tlat 1Ar7 tltat !ra2, au9 l.l !ilItt ottra ,oL6t ltaJt r.at !!tl5 toa2n 7a7?! rttD a!tt7 aa?D 227a2 stt! tttv ,art t rtt Iu ato4 at!9 tttcrn 0&4 t&tr ?. la o la? te latg laatal aop !atn t!. t tl !?oQ trtt! 50y clart lo.atr ,'ll7 9xtl !f$ aaiaa rarz, artttT raTaj au'' artto at, ttatt alrtra a torul4 L tr 72rp I tt tt? a ta, t4 aatg ltrs 5&tt ?NN ,a.il1, l l! r29 ogtQ rDtt atr{ 12 I rrfr( aay, Jaaaa aTttt! tJt l2aat tt( i 7aF !!?tt a0c 'lr{a!?rrtr? l2t 125 atll! atro l!t zrt! l{t !o7tB !tltta ,, @taa ttaia ,,, !nx jta tt.tc g, lttr Itax roatl tt at trtt rroJott tra !.r! a9r It tl trara t ttatt J' J' !xa a ttt, tt6t rat oltt I ,D& a tat i! n) tto I arra ,tat? 6I r&a, Grrl t lsq at a, tta I aro axn rl tt rtt, n FOtJ 7tcc, oa2a E{ arrtt !.! ts ltl ?raF arntr oo tta o lLfl t!r{ 476 ,T' a aaalt latt6 T' Itta a t i6 tt! otttt [! e!& a Ittla !!?x r7 rl ttI I lsL aatJl rtt allta afltt tl.a o ftttl ?[t? fats a!att utat a$!a c - ttt nal It!!t ?ratt o ail !lta ta6 la.' c I ,, ,rtn lst ttx c tl TO ltt' )ttl ttt!s jax t o $a tr! , tta tr I t Ilt r.tl aoa ts6 I E ttl aatt trt' aat I t llt! rtt r|'ttt rla t I ax tan al''' , a a, CRYSTAL STRUCTU RE OF TINCAI'CONITE 525 Parameters(Xltr)*' Tlsls 2. Fractional Atomic Coordinates (Xltr), Anisotropic Thermal (1959) and Equivalent Isotropic Thermal Parameters according to Hamilton br bzz ol3 oi, o, ori Btt x r z r I 7Q) 19 1(3) 1 1.38 Na(1) 0 6695(5) 50 t8(6) 40(4) 12(5) 14 0 0 1.41 Na(2) o o50 29(7) 29 21(4) 38 0 0 3.08 Na(3) 0 o 928(5) 75(6) 75 4(r) 22('to) z6) 1(5) o,94 B1 926(11) 2676(12) 38zD(7) zz(11) 43(12) tz(t) 19(1o) 4(5) 4(6) 1.18 B2 2385(12) 585('t2) 2882(9) 36(12) 24('t2) 2 -5(4) -3 u.oo o(1) o 5134(8) o 4(9) 13(7) 7(4) (?) 1 1o(3) o(6) 7(3) 1.31 o(2 ) 325(7) 2911(7) 2526(4) 31 4(7) 19(7) 6(4) 15G) 3(4) 2(3) 1.13 o(3) 21290) 421(t) 35ol( 5) 43(8) 6(3) 21(5) 4(3) 2(l) 0. 9l oH(+) 1281(7) 1g4z(7) 4290(4) 39(?) 17(7) 17(4) 86(11) lo(6) 21(4) 3.27 on(5) 25to(12) 1?94(8) 2577(5) 1?o( 1 5) 54(9) 44(8) -9(4) -4(4) 1.89 ow(6) 885(8) z2\e) 1il9(4) 75(9) 56(10) 5(l) o'(7) o 8620(28) o xTheestinatedStandarddeviatronsaregiveninparentheses.Thetemperaturefactors ' refer to the expresslot, e*p1-br.,h2 +brrkz+brarz+2(btrhk+brrkl+b',rhr)') synthesisshowed only fining one. The generatedphases were then refined A three-dimensionalFourier for Ow(7), a position by cyclic applicationof the tangent formula.