Canadfun Mircralogtst Vol. 16, pp. 75-80(1978) REFINEMENTOF THE CRYSTALSTRUCTURE OF HVDROBORACITE CESARE SABELLI AND ANDREA STOPPIONI Istituto di Mineralogia dell'Universitd., Via Iamarmora 4, Firenze, Italy ABsrRAcr glu (1973); this autlor s0udiedthe changes oc- cu.rring i,n the structure upon loss of water and Three-dimensional counJer-diffractometer X-ray found also that the hardness of the Turkish data aud full-matrix least-squares have been used mineral is 5-6 according to Mohs' scale' whereas to refine the crystal structure of hydroboracite, et al. (L951) reported its hardness to CaMglBgOn(OH)312.3$zO, wit! a 1L,769(2), b Palache 6.684(2), c 8.235(4)L, p 102.59(2)', Z=2 in space range between 2 and 3. group F2/c. The final R for 1428 reflections is An indexed powder pattern together with the O,042. T\e structure proposed by Rumanova & unit-cell dimensions were given by Cipriani Ashirov (1964) has been confirmed. The basic re- (1958), who also describedthe thermal behavior peat unit of the structure is the [BgOa(OH)g]L group of hydroboracite. Rumanova & Ashirov (1964) consisting of two tetrahedra and one triangle; these gave a correct solution of thti structure on the borate polyanions are polymerized into undulating basis of photographic data. chains along c. Chains of corner-shared Mg(OH)e- (IIzO)a octahedra are linked to boron-oxygen charns giving sheets parallel to (100). Chains of edge- ExPBRTIvIENTAL shared CaOn(OH)n polyhedra also run parallel to the c axis and connect the sheets to each other. The crystals of hydroboracite used in this study come from the Bigadic mine, Balikesir, Sorvrrvrenr Turkey. Indexed X-ray powder data are given in Table 1; indexing was performed, through Irs donn6es tridimensionnelles obtenues aux rayons X sur diffractomltre i compteur ont 6t6 uti- lisfus pour affiner, par la m6thode des moindres carr6s i matrice entibre, la structure de I'hydrobora- TABLE 1. X-RAI POWDEI DII'FRACItON DAIA FOI SYDROBORACIIET cite, CaMglBgOr(OH)slz.3HO: a 11.769(2), b 6.64(2), c 8.235@)4,, p 102.59(2)' Z - 2, groupe htl d""t"i dobri I h 1 d""1"1 dobrl I spatial P2/c. Le r6sidu final pour 1428 r6flexions 100 r1.486 4 2.L78 2.181 I est 0.042. La structure propos6e par Rumanova & o to 6.69 85 2.L72 2.L72 6 Ashirov (1964) est confirm6e. Dans la structure, Ie 110 5.78 100 1 2.o49 2.088 011 5.14 I -4 2.063 2.063 groupement anionique [83O4(OH)r]'?- est form6 de 4.96 6 2.O57 2.O57 polyanions lt1 4 .464 I 2,O21 2.O27 deux tdtraddres et un triangle; ces sont 210 4.36 13 I polym6ris6s suivant c en chaines ondul6es. Des oo2 4.O18 4.O2 I l:333r.ee6 300 3.829 1.974 r.974 chaines d'octaldres Mg(OHLGIzO)a i sommets com- -202 3.592 3.69 2 -3 L.964 1. 968 3. 589 1.949 muns sont reli6es i des chalnes bore-oxyglne for- r'Yqu 3.56 1 I r.951 mant ainsi des couches (100). Des cha?nes de poly- ot2 1.926 L.926 paralldles 31.0 3.32 74 1.914 1.914 16 bdres CaOa(OH)e i a€tqs communes sont 1. 845 I c et relient les couches entre elles. L L2 3.141 3.L4 -4 1.846 ''644 ' -1 t 1 3. 045 3.05 -6 I t.824 r..827 I (Iraduit par la R6daction) 20 2 3.000 3.00 1.789 1.788 I L2T 2.9 L9 2.921 -L I.770 L.769 2 3ll 2.447 0 L.722 I.722 L 4oo 2.47L 2.873 2 1.715 INrr.ooucrroN 2.838 2.437 I L.7L7 -4 I 1 2.670 2.670 0 1.671 L.67L 7 410 2.637 r.551 L.66L 2 2.624 I 4 1.654 2.530 L z As a part of the systematic investigation of -402 -7 1.650 r'o)r 3 20 2.518 2.517 2 7 the crystal structures of hydrated borate com- o13 2.487 2.486 7 3 o 1.638 2.472 pounds, a refinement of hydroboracite, CaMg- L22 2.436 L4 t .604 500 2.297 7 1.594 1.593 3 fBgOr(OH)sls'3HzO,was performed. Several oc- 222 2.232 2.228 12 t.))) o30 ? .224 2.223 4 r.554 currences of this mineral, commonly with other -5 1 I 2.2L5 1 1. 543 1. 543 1 borates such as colemanite, inyoite, inderite and -5 0 2 r.539 1.539 1 130 2.!47 2.L87 L ulexite, are described in the literature. Recently, *Pblllp" an occurrence of hydroboracite in Balikesir p*d.r dl.ffrect@ater' co isallatloB, fe fllter, l' 20 Per Dt& province, Turkey, was described by Demircio- range 5" 5 20 < 70". 75 76 THE CANADIAN MINERALOGIST TA3LE 2, CRYSTALLOCT.APNlC DATA AND OTIIDR INIORYAIlON trolled diffractometer using MoKa ra.driationand the a-20 scantechnique. A total of 1846 indepen- dent reflections in the range 3o<20(30o Folou1a unit, caMg [8304(oF)31 were r.:uro measured;a reflection was consideredto be ob- a - 11.769(2).& crvstal size: o.35xo.o9xo.05 (@) served if its intensity was greater than five stand- - b 6.684(2) i ra alfittert rro/zt ard deviations based on counting statistics. Ap- c - 3.235(4) i plication roral no. of lrol : 1846 of this procedure gave 1428 observed p - 102.59(2). reflections. Intensities were conected No. of lr.ol> 5s : 1428 for I-e. rentz-polaization effects, rrhereas absorption Spaee group P2/c Z - 2 correction was considered negligible becauseof V - 632.3 i3 p(UoKa) : 6.3 cr-1 the crystal's thinness. D obs - 2.15 gcn-3 tinaL R (ob6erved):O.042 D calc- 2.170 gcn-3 Fioal F (a11 data): O.060 STRUcrr.rRERnrtNnptBivr o -f1lj rol _ Incllvflrol The refinement of the structure was started Tenpe!atu!e fdctor fore used: using the atomic coordinates of Rumanova & u*p{-(Frrh2r prrt2+z Ashirov (1964) and giving P,ru2+ 3rr*rz Plrlrr: 82rr.DI each atom a I value obtained by averaging the B's found by these authors for different layer-lines of Weissenberg repeated cycles of cell-constant refinements, data. with tle aid of single-crystalintensities. The re- One least-squaresfull-matrix refinement oycle fined parameters,based on 6L lines, are reported with isotropic thermal parameters and two sub- in Table 2. T\e observeddensity, determined by sequent full.matrix cycles with anisotropic ther- the flotation method, is 2.159 cm{ and the calcu- mal parametersled to a residual index R:0.M8. lated value, 2,l70g cm{. Intensitieswere collected At this stage of refinement a difference Fourier with a Philips PW 1100 4-circle computer-con- synthesiswas computed in an attempt to direct- iy locate tlte six hydrogen atoms of the structure. Since the O-O distance analysis showed an un- ambiguous hydrogen-bonding system, tle resi- TABLE 3. TRACTIONA', ATOMIC COORDINATDSAND ISOTROPIC TEMPERATURET'ACTORS Atoe n ti2r !tg 0 0 0 0.75 ca 1"/2 0.47388(9) L/4 O.52 ** o (l) 0 0.1238(3) L/4 1.01 0(2)** 0.0504(2) o.2772(3) 0.5966(2) 1.37 N: o(3). 0.1667(1) 0.906r(2) 0.5359(2) o.99 0(4) 0.1910(1) o.3419(2) o.2468(2) 0.80 0(5) 0.1758(l) o.5515(2) o.4678(2) 0.89 0(6) 0.3487 (1) o.7299(2) o.6052(2) 0.80 0(7) 0.3266(1) 0.6114(2) o.3209(2) 0.87 0 (8)* 0.3544(1) 0.9672(2) 0.3936(2) 1.16 0(9)* 0.5093(1) O.7160(2) O.47t7(2) O,97 3(1) o.2251(2' O.7125(4) 0.59t2(3) O.Ot B(2) 0.3848(2) 0.7614(3) 0.4480(3) o,69 B(3) o.2325(2) 0.5039(3) 0.3436(3) o.63 H(1) 0.064 0.197 0.249 4,5 H(2) o.o92 0.370 0.554 4.5 l1(3) -0.025 0.335 0.575 4.5 E(4) o .230 0 .927 0.489 4.5 B(5) 1.069 o.298 Frc. 1. Projection of the structure down the D axis. H(6) o.446 o.L79 0.483 Half-cell rn ,r is represented. Open circles and small black circles indicate oxygen and hydrogen Bt€ ol the non-hydrogeo atoms a!e the equivalent oires atoms, respectively. after HaEilton(1959). *O to 0Et rro 10 rater Dolecule€ STRUCTURE OF }TYDROBORACITB 77 IABIB 6. ANISOTROPICTEWESATURE TAC1OR COTTTICISNTS* TABLE 5. SELECTEDIN1EPATOYIC DISTINCES AtoE ? tt Pt, F., Pr" P,t Pn Ng octahedlon B(1) tetrahcdlon us-o(1),o(1iv) z.zrg(r) i B(1)-o(3) 1.491(5) I (g) Ms 123(1) 363(22) 383(15) -26(10) 62 (8) -1.6(X4) us-o(2vi),o(2ix) 2.554(5) s(r)-o(ctit) r.aeg Me-o(3""")'0(3-) 2.o2o(6) B(r)-o(5) 1.508(8) ca 78(4) 359 (r3) 224 (9) o 64(5) 0 B(1)-o16) 1.440(4) Uean 2.098 o(1) r75(15) 605(47) 439(34) o 121(19) 0 YeaD 1.411 Ca Dolvhedron o(2, 224(13') 619(34) 750(29) 49(76') 152(15) 80 (25) !*f,fitflo."tii; z.:rr{a) o(3)-o(4'"') 2.374(\) (32) (26) -75 (15) -2LL(22) 0(3) 154(11) 584 482 132(L3) ea-o(7),o(7v) 2.425(4) o (3)-o (5) 2.446(2) 2.4o4(9) 0(4) 163(11) 5L3 (32) 297 123' -7 4 (L4) 131(r3) -48 (20) ca-o(9),o(9v) 2.424(3) o(3)-o(6) cr-o(gii),0(g"iii1 z.ea:{:) o(auii)-o(:) 2.374<4) 0 (5) 149(r1) 603(32) 35r(23) 69(15) rr6(15) 134(21) o(r,"ti)-o(o) 2.446(9) UeaD 2.461 o (6) r35 (1r) 54r (31) 298(22) -19 (14) ?i/1r\ r<a?ll o(5)-o(6) 2.4re(e) (3) -109 B triaDsle 0(7) 140(10) s7o(32) 366(23) -65 (1s) 113(12) (22) rean 2.410 E (3)-o (4) r.,312<6) (33) (24) -21 (16) 67 (13) r45(23) o(8) 262<L2) 534 433 B(3)-o(7) 1..367(4) B (2) tetr€hedron 0(9) x44(X2) 524 (3L) 496(26) -7 2 (15) 96(L3) -L24(22t B(3)-o(5) 1.314(9) B(2)-o(6) 1.46r(8) 1.5o2(9) E(r) 131(16) 408(45) 217(33) -24 (21) 36(18) 4 (30) l{ean l.