The Crystal Structure of Tincalconite'

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 relations 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 obtained 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. A con- a broad maximum suitable synthesisunambig- sistent set was employed for increasingto 150 the where a later Fourier difference H positions were deter- reflections with > O.7 that had known phases. uously located this atom. lEl distances' The R6r"L, RD**, a, ?trd t citeriz were employed mined by inspectionof interatomic the H atomswere (Kennardet al,1971'),where Isotropic temperaturefactors of and inclusion of hydrogen atoms and -lrol""'"1 fixed at 3 A' r\Ka'rcD --Illrol Ow(7) reducedthe R valueto 0'08' Refinementwas E tat using anisotropic thermal parametersfor - continued E tat (1 ro) all atoms except Ow(7) and the hydrogen atoms' D_ r\Drew - S high value of the Ow(7) temperature factor /- lEhl The The final 1- 17 A'?) can be explainedstructurally. R index for 337 observedreflections is 0'06 (or 0'07 for 398 includingthe non-observedones)' The final positional and thermal parametersare listed in Table I : cos(sr* ,pr-r) ; lE*l lEo-*l 2. H positionsare shownin Table 3. The atomic scat- factors used were those given by Cromer and a : E lEnl lEo_nlsin (eo* po_*) tering Waber(1965). a : lEol(A" + Br),,,

During the calculationsa phasewas consideredas TesI.e 3. Fractional Atomic Coordinates for the Hydrogen (X determinedif a ) 8. The best R6..1" &rrd Rp'u* Atoms lCF) values of 0.28 and 0.25 respectivelyoccurred in one of eight attempts.The map obtainedfrom the properly Atom phased .E values confirmed the positions of the Na 1 4015 uto*t located by the Pattersonsolution and showed --1H 1581 411 atom, Ow(7) all of the atoms, except one oxygen --2T{ 2383 2367 2859 and the hydrogen atoms. The atomic parameters 2484 1766 and the individual isotropic temperaturefactors were H. 684 full matrix least-squares 1151 refined using a modified "4H 425 2743 program onrls (Busing et al, 1962). The R - fi 515 8217 9747 E ltnt lF,ll/ElF.l valtteafter this refinement was0.10. 526 GIACOVAZZO, MENCHETTI, AND SCORDARI

Description of the Structure Tnsrr 4. Na-O Bond Lengths (A) with Their Standard Deviations in Parenthesesand Their Multiplicities in Braces The structure is illustrated in Figure 1; for clarity, this picture is a simplification its of overall three- Na(1)-0H(4) lxzl 2.ail(7) Na(2)-oH(4) lx6l 2.4t9(6) dimensional character. The complete arrangement -0w(6) {x2} 2.453(7) Na(l)-ow(6){xl} 2.318(B) of the atoms in tincalconite can be obtained easily -oH(5) {x2} 2,442(8) -0w(T) {x3} 2.518(18) when projecting the structure on (010) of the C- centered orthohexagonal cell. Each of the three crystallographicallyindependent sodium atoms is with two Na(3) polyhedra through the two remain- coordinated by six oxygen atoms (including OH, ing water oxygensOw(6). H,',O). Interatomic distancesand bond angles are The Na(2) atom is surroundedby six hydroxyls given respectivelyin Tables 4 and 5. OH(4) with the cation-anion distance2.42 A; the The oxygen atoms around Na(1) form a nearly shape of this polyhedron is a slightly distorted octa- regular octahedron.This Na(l) octahedron shares hedral arrangement. two hydroxyl corners OH(5) with two adjacent The Na(3) atom is surroundedby six water oxy- BO,r(OH) triangles and two hydroxyl corners gen atoms, This polyhedron shares a face, built up OH(4) with two adjacent BO,,(OH) tetrahedra. by three Ow(7) water oxygens,with an equivalent It shares one edge, OH(4)-OH(4'), with the Na(3') polyhedron and three corners Ow(6) with Na(2) polyhedron. This edge is 3.25 A, the short- three Na(l) octahedra. This connection is rather est one in the Na(1) octahedron,while the oppo- unusual but already known (Corazza et al, 1967). site edge OH(5)-OH(5') is the longestone (4.07 The Na(3)-Na(3') distanceis very long, 3.90 A, A). Finally the Na(l) octahedron shares corners compared with the distances for regular Na-oca- thedra sharing one face, 2.80 A. Moreover it is longer than those reported in the literature, 3.30 A (Frevel, 1940; Miller, 1936; Grund and Preisinger, 1950), and 3.15 A (Corazzaet al, 1967). The in- creaseddistance and the irregularity of the Na-poly- 2a+bj hedron are attributed to the electrostatic repulsion betweenthe Na(3)-Na(3') cations and particularly to the stress of the "Na-chains" (Fig. 1). The Ow(7)-Na(3)-Ow(7') angle is 66.3o, whilst Ow(6)-Na(3)-Ow(6') is 106.8". The Ow(7)- Ow(7') and Ow(6)-Ow(6') distancesare respec- tively 2.75 and 3.75 A. These results are in good agreementwith the con- clusionsof Cuthbert and Petch ( I 963b ) .

Tesl-r 5. O-Na-OBond Angles(.) with Their Standard Deviationsin Parentheses

O-Na-o Angle O-Na-o Angle

ow(6)-Na(1)-oH(5) 94.0(J) oH(4)-Na(2)-oH(4') 85.5j(2) -oH(5') 89,J(j) -oH(4") 84.r7(2) -oH(4) 81.6(2) -oH(4"! 106,95(3) -0H(4') 92.2(2) on(fv)-rv'(z)-on(cv) r el. jl(+) oH(5)-Na(1)-0H(5' ) 113.5(4) 0w(6)-r,ra(l)-ow(6') 106.82(3) -oH(4) 164.2(3) -ow(7') 102,60(l) 0H(a)-ra(1)-0u(5) 82.6(2) -ow(7) 79.81(2) -0H(4') 81.8 (l ) 0w(7')-Na(l)-0w(7) Frc. 1. Projectionof tincalconitestructure on (010) of the 66.3j(z) 0w(6'FNa( 17 -0w(6) orthohexagonalcell. Dotted Iines indicate some of the 1)-0w(6,') 4.5(4) 121.90(3) hydrogenbonds. ow(7)-Na(3)-0w(6) 179.92(4) CRYSTAL STRUCTURE OF TINCALCONITE 527

Ftc.4. Projectionof Na-octahedrain tincalconite on (001)'

tancesand bond anglesare in good agreementwith those given for the [B+Or(OH)+]-'?borax polyion (Table6). HYdrogenBonds No attemptto locatehydrogen atoms directly was hkl FIc. 2. [B*O,(OH),]-'polyanion in tincalconite' madebecause of the low numberof independent reflections.However, from an inspection of the anion-aniondistances we found someO-O distances In tincalconite the same boron-oxygen polyion less than 3.20 A for oxygensnot belongingto the occurs as in borax, and it is crossed by a two-fold samepolyhedron (Table 7)' axis in both structures. The polyion is formed by On the basis of O-O distance,the location of two symmetrical BO''1(OH) triangles and two sym- hydrogen atoms confirms Christ's rule that in the metrical BOB(OH) tetrahedra to give a compact group with composition [B*O;(OH)+1-: 1Fig. 2). Within the borate polyion, each of the BOI(OH) c triangles shares O(3) and O(2) oxygens with the bl BO3(OH) tetrahedra, which are in turn connected to each other by the sharing of O( 1). Interatomic dis-

c af

FIc. 3. The structure of borax projected on (010). Some of Na-octahedra in borax on (100) of the hydrogen bonds are shown by dotted lines (Mori- Frc. 5. Projection (Morimoto,1956)' moto. 1956). GIACOVAZZO, MENCHETTI, AND SCORDARI

TenrB 5' Comparison of B-O Distances and Angles in TesrE, 7. O-O Distancesless than 3.20 A for Oxygens not Borax and Tincalconite Belonging to the Same Polyhedron in Tincalconite

Borax Ttncafconite N. Morrnoto (1956) Thls study oH(4)-0(3) 2.834(e)i ow(T)-oH(5) 2.965Q1)8 Distances(A) (i) Atons Atons nistances oH(5)-o(1) 2.665(9) ow(6)-0(2) 2.758(1o) ^F rhdldcrol or angles(o) 0w(6)-0(z) 2.845e)

B-0 Dlstances -3o

B(1)-o(1) 1.47 B(1)-o(1) 1.460(12) example, the reaction boru" tincalconite is -o(2) 1.46 -0(2) 1.468(12) -0(l) 1.54 -0(l) 1.507(13) easy and reversible,but trr".uJolversion borax- -oH(4) 1.46 -0H( 1.454(1j) 4) tincalconite into kernite is difficult. These authors B(2)-o(2 ) 1.36 B(2)-o(2) 1.358(14) -o'(3) 1.32 -0(l ) 1.130('t5) state that this difficulty is related to a considerable -oH( -0H( 5) 1 .40 5) 1.j86(13) activation energy for the conversion of borax- O-B-0 Angfes tincalconite into kernite, perhaps because kernite o(1)-B(1 )-o(2) 111.2 o('r)-B(t)-o(2) 109.3(7) 0(1)-B(1)-0(3) 108.6 -0(l) ioB.t(9) does not contain the same polyion [BnOu(OH)n]-' -0H( 4) 110.2 -0H( 4) 1't1.917) as borax and tincalconite, but instead has infinite 0(2)-B(1)-0(l) 108.5 o (2)-B( 1 107.1(7) '111.5 )-o(l ) _oH(4) -0H(4) 110.5(9) chains of composition[BnOu(OH)"1-'", as was later o(3)-B(1)-oH(4) 106., o(l)_B(1 )_oH(4) 11o.7 (7 ) confirmed experimentally(Cialdi et al, 1967;Giese, (2 o(2)-B )-0"(3 ) 125.3 0(2)-B(2)-o(l) 122.9(10) 1966). -0H(5) 117.0 -0H(5) 120.1(10) 0,'(3)-B(2)-0H(5) 118.7 o(3)-B(2)-oH(5) 11 6.2(1O) In the light of structural results, the general ar- rangementof atoms in borax, tincalconite, and kernite can be compared.The borax structure,space polyions of hydrated borates those oxygens not group C 2lc, is built up by chainsalong the c direc- sharedby two borons alwaysattach a proton to form tion. One set of chains is composedof Na.6HzO a hydroxyl group. So the hydrogen atoms were lo- polyhedra sharing edgeswith each other in the rc cated at 1 A from the oxygen atoms surrounding plane (Fig. 3). The other set of chains is formed Na-polyhedra,along the vectorsO-O reportedbelow by hydrogen-bondingbetween the discrete [BaO5 (Table7). (OH)ul-' polyions which are located betweenthe Na polyhedraand connectedto them by hydrogen Comparisonof Tincalconite,Borax, and bonds. Kernite Structures In tincalconiteand in borax,it is possibleto iden- tify similar structural units, but because of the Christ and Garrels(1959) in their paperon sodium lesser water content packing borate hydrates explain the apparently anomalous and closer of tincalconite, the following (Figs. behavior found for the NarBnOr-HrOsystem. For differences are noted 1,3,4, 5). 1) The "Na-chains"in tincalconiteare distorted comparedto borax. The interaxialdistance between two "Na-Na chains"in tincalconiteis 6.97 A (Fig. 1), whereasin boraxit is 11.36A(Fig. 3 ).

Tenr"e 8, Charge Balance of Oxygen Atoms in Tincalconite (Ionic Structure)

Aton Ba Bo tCa(t) Na(2) Na(l) -H... ..H- Tota}

0(1)... 2x3/ 4 2x1/4 2.0O o(2)... 3/4 2x1/4 2.25 0(l)... 3/4 1/+ 2.oo 0H(4).. 3/4 1/6 1/6 3/4 1.83 0H(5).. 1/6 3/4 1/+ 2.'t6 ow(5).. 1/6 1/6 zx3/4 1.83 Frc. 6. Boron-oxygen chain running along the bisector of 0w(7).. 2x1/6 2x3/4 1.83 monoclinic angle in kernite (Cialidi el al.,1967). CRYSTAL STRUCTURE oF TIN1ALC}NITE 529

2) Tincalconite shows a rotation of Na(3) poly- which are in turn linked to boron-oxygen chains' hedra, forcing them to share one face. As mentioned Finally, although differences between borax and above, the working conditions were close to the tin- tincalconite exist, both are quite different from ker- calconite-boraxconversion, (6AVo R.H., 20-25'C). nite because of the polymerization of the [B+O'r The high thermal parameter of Ow(7) must result (OH)nl-' polyions and the "islands" of sodium-oxy- from the instability of face-sharing between two gen coordination. These features are the most im- Na(3) polyhedra. The transformation of tincalco- portant ones that explain the easy and reversible nite to borax can be considered as starting from the equilibrium of borax ? tincalconite and the more a break of such face-sharingconnections. difficult transformation of borax-tincalconite 3) In tincalconite, hydroxyl groups are shared kernite. between [B4O5(OH)4]-'z polyions and Na polyhedra. Four OH groups belonging to the polyion are Acknowledgment shared by four Na-polyhedra belonging to four dif- We wish to thank Dr. Joan R. Clark, U.S. Geological ferent "Na chains" to build up the three-dimensional Survey, for her interest in this work and for helpful sug- structure, gestions. Under the assumption of an entirely ionic structure, the charge balance of oxygen atoms in borax References can be compared with that of oxygen atoms in BRAv, P. J., J. P. Eowlnos, J' G. O'Kr:rnr, V. F. Ros, resonance tincalconite, as shown in Tables 8 and 9. Distributing eNo I. Terouzun (1961) Nuclear magnetic studies of Bo in crystalline borates. J. Chem. Phys' 35, each hydrogen contribution as 3/4 ta the linked 435. oxygen atom and I/4 to the unlinked one, the bal- BusrNc, W. R., K. O. MenrrN, AND H' A. Lrw (1962) ance comparation between borax and tincalconite is oRFLs,a Fortran crystallograpbicleast-squares program' satisfactory. tl.S. Nat. Tech. Infor. ,Seru.ORNL-T-305. On the basis of the crystal structure determination Cnnrs:r, C. L. (1960) Crystal chemistry and systematic (Giese, 1966; Cialdi et al, 1967), kernite is very classificationof hydrated borate minerals. Amer. Mineral different from borax and tincalconite. Indeed kernite 45,334-340. polyions is built up of boron-oxygen chains which can be con- lNo J. R. Crlnr (1957) The nature of the in some borate minerals. GeoI' Soc. Amer. BulL 68' 1708. sidered as the polymeization reaction of borax poly- .lNo R. M. Gemus (19'59) Relations among so- ions (Fig.6), dium borate hydrates at the Kramer deposit' Boron, California. Amer. l. Sci. 251, 516-528- n [BaO5(OH)n1-'?: [BnOu(OH)"f*-'"* nH"O Cr.rror, G., E. Con,rzz.l,,eNn C. S.lsrnr (1967) La struttura Kernite has two crystallographically independent so- cristallina della Kernite, Na,B,O"(OH)"'3H,O. Acc. Naz. dium atoms Na(1) and Na(2). Na(l) is sur- dei Lincei Fasc. 2, Serie VIII, Yol. 42. rounded by three water molecules and two oxygen Conltzzt, E., C. SesEnr, eNo G. GrusrppETrr (1967) The Acta atoms. Na(2) is surrounded by three oxygen atoms, crystal structure of lecontite, NaNH.SOI'2H"O' Crystallogr. 22, 683-687. one hydroxyl atom and one water molecule. Four D. T., .rNo J. T. Weern (1965) Scatteringfactors such Na polvhedra are connected to form "islands" Cnousn, computed from relativistic Dirac-Slater wave functions. Acta Crystallogr. 81' 104-109. Tesr,e 9. Charge Balance of Oxygen Atoms in Borax (Ionic Curunent, J. D., .lNo H. E. Percn (1963a) N.M.R' studies Structure) of hydrated sodium tetraborateminerals' I' Boron-Oxygen polyion in borax and tincalconite. I' Chem. Phys. 38, Atom BABo Na(t) ta(e) -it...... H- Totaf 1912-19'19. AND- (1963b) N.M.R. studiesof hydrated 0(1)... 2x3/ 4 2x1/4 2.O sodium tetraborate minerals. II. Na sites in borax and o(2)... 1 t/q 3/4 2-o tincalconite. l. Chem. Phys. 39, 1.247-1252. 0(3)... 1 3/4 2x1/+ 2.25 Fnrvr,r-, L. K. (1940) The crystal structure of sodium sul- 0H(4).. 3/4 3/4 2x1/4 2.oo fate. III. l. Chem. Phys.8,290. nHi/F\ 1 3/4 2x1/4 2.25 GTESE,RossMeN F., Jn. (1966) Crystal structure of kernite, o(6)... 1/5 1/6 2x3/4 1.83 Na,B*O.(OH ),' 3H,O. Science,154, 1453-1454. o(7)... 1/6 1/6 2x3/4 1.83 o(8)... 1/6 2x3/+ t/q 1.92 Grnsn, Rossvrer*F., Jn. (1968) A refinementof the crystal 0(e)... 1/6 2x3/4 1/4 1.92 structureof borax, NarBoO'(OH)n'8H"o. Can. Mineral. 9, part 4, 573. 530 GIACOVAZZO, MENCHETTI, AND SCORDARI

GnuNo, A., exo A. PnrsrNcrn (1950) Uber die Kris- MIlr-rn, J. J. (1936) The crystal structure of anhydrous tallstruktur des Natriumthioantimonats,Na"SbS,.9H,O sodium cromate, Na,CrO,. Z. Kristallogr. 94, 13l-136. Schlippe'schesSalz). Acta Crystallogr. 3, 363-366, MINnrn, W. (1935) Uber den Bau eininger Hydrate von H,rvrlroN, W. C, (1959) On the isotropic temperaturefac- Natriumdiborat. Z. Kristallogr. 92, 301-309. tor equivalent to a given anisotropic temperature factor. MontIvtoro, N. ( 1956) The crystal structure of borax. Acta Crystallogr. 12, 609-610. Struct. Rep. 20, 376-380. INvERs,G. A. (1948) Estructurede la tincalconita(Moha- Persr, A., ANDD. L. Sewypn (1948) Tincalconite crystals vita) Na"B*O,.5H,O. Estudios Geologicos,Istituto Lucas from Searles Lake, S. Bernardino County, California. Malada.7,27-40. Amer. Mineral. 33, 472481. Kenle, J., lNo L L. K,rnrs (1966) The symbolic addition Perlcne, C., H. BrnvlN, eNo C. FnoNoEr (1951) Dana's procedure for phase determination for centrosymmetric Systemol Mineralogy. Vol. II, John Wiley and Sons,Inc. and noncentrosymmetric crystals. Acta Crystallogr. 21, Psrcn, H. E., K. S. PerrrrNcroN, lNl J. D. CurHstnr 849-859. (1952) On Christ's postulated boron-oxygen polyions in KrNNeno, O., D. L. Weurren, J. C. Coppole, W. D. S. some hydrated borates of unknown crystal structures. MoTHERwELL,D. G. WATSoN,eup A. C. LensoN (1971) Amer. Mirteral. 47, 4Ol-404, The crystal and molecular structure of cis-trans-ciscy_ clodeca-2,4,8-triene-1,6-dione. Acta Crystaltogr.27, 1116- Manuscript receiued,September 5, 1972; acceptedfor 1123, publication, December 14, 1972.