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A. E r t l, F. P e r t l i k, and H.-J. B e r n h a r d t

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Anzeiger Abt. I (1997) 134: 3-10 Anzeiger Mathematisch-naturwissenschaftliche Klasse Abt. I Biologische Wissenschaften und Erdwissenschaften Akademie d. Wissenschaften Wien; download unter
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Anzeiger Abt. I (1997) 134: 3-10 Anzeiger Mathematisch-naturwissenschaftliche Klasse Abt. I Biologische Wissenschaften und Erdwissenschaften Akademie d. Wissenschaften Wien; download unter Österreichische Akademie der Wissenschaften 1998 Printed in Austria Investigations on Olenite with Excess Boron from the Koralpe, Styria, Austria By A. E r t l, F. P e r t l i k, and H.-J. B e r n h a r d t (Vorgelegt in der Sitzung der math.-nat. Klasse am 18 Dezember 1997 durch das w. M. J. Zemann) Abstract Chemical analyses of tourmaline crystals from a small pegmatite body, nearby the Stoffhütte, Koralpe (Styria, Austria), exhibit a pronounced excess in boron, expressed by the simplified formula (Nao.43Cao.24Q0.33) (Al2.43Lio.33Qo.28)Alö(B03)3(Bi.23 Si4.g7 Oi8)[O0.64(OH)3 36]. A substantial substitution of silicon by boron in the tetrahedral position is in agreement with an occupation refinement in single crystal X-ray work: the average (Si, B )-0 bond length measures A. This is the first example for a substitution of silicon by boron in a natural tourmaline, that could be verified by crystallographic methods. Zusammenfassung Chemische Analysen von Turmalinkristallen aus einem geringmächtigen Pegm atitkörper, in der Nähe der Stoffhütte, Koralpe (Steierm ark, Österreich), zeigen einen ausgeprägten Überschuß an Bor, der in der vereinfachten Formel (Na0.43 Ca0.24 Qo.33)(Al2.43 Lio.33Qo.2s) A16(B 0 3)3 (Bl.23 Si4.87Oi8)[O 0.64(C)H)3.36] seinen Ausdruck findet. Ein substantieller Ersatz des Siliziums durch Bor in der Tetraederposition steht mit der Verfeinerung der Besetzungsdichte anhand von Röntgen-Einkristallda- 4 A. E r t i. et a l. Akademie d. Wissenschaften Wien; download unter ten in Übereinstimmung: die durchschnittliche (Si, B)-0-Bindungslänge beträgt A. Dies ist das erste Beispiel für den Ersatz von Silizium durch Bor in einem natürlichen Turmalin, der durch kristallographische Methoden bestätigt werden konnte. Introduction A survey on tourmalines from Austrian localities, including lattice constants, semiquantitative EDX-analyses, as well as the compilation of morphologic and genetic aspects (E rtl, 1995) drew attention upon the lattice constants of light green, blue or even colourless tourmalines from the Koralpe, Styria, Austria (cf. M o se r and P o st l in N ie d e r m a y r et al., 1986); P o st l and M o se r, 1987; P o st l, 1988). The small values of the lattice constants [ag= (1) A, cg= 7.061(1) A] and preliminary chemical analyses led to the assumption that the [9 + 1] coordinated alkaline and/ or alkaline-earth-position in the structure is unoccupied. The tentative formula AlßA l^bc ^SiöO ^O, OH)4 was proposed. But the quantitative chemical analyses of the present study show appreciable contents of sodium and calcium, hence the composition of the investigated material is close to an olenite end-member tourmaline (seetable 1). The coherency of lattice constants and chemical composition was the reason for further investigations by a detailed structure determination. The average size of these olenite crystals varies from 2 to 5 mm, some aggregates of parallel arranged crystals are up to 25 mm in length. The larger individuums are sometimes intergrown with schorl. Experimental The chemical composition of the present tourmaline was determined by atomic absorption spectroscopy for lithium, the Karl-Fischer titration techniques for H20 and electron microprobe analysis for all other elements. The following standards were used for the microprobe analyses (elements and lines in parentheses): jadeite, (Na Ka), K-glass (K Ka), topaz (F Ka), pyrore (Mg Ka, Al Ka, Si Ka), andradite (Ca Ka, Fe Ka), spessartine (Mn Ka), rutile (Ti Ka) and dravite (B Ka). The operating conditions for fluorine and boron were 6 kev accelerating voltage, 30 na beam current, all other elements were measured with a beam of 15 kev and 15 na. For both conditions a beam diameter of 8 im was used. Scans around the B Ka line using a PC2 pseudo diffracting crystal proved identical line positions and shapes for boron in both the dravite and the olenite sample. The B Ka-peak of our tourmaline was about 20% higher than that of dravite. The analyses were corrected by applying the Cameca Investigations Akademie on Olenite d. Wissenschaften with Excess Wien; Boron download from unter the Koralpe, Styria, Austria 5 PAP procedure. Special care was taken to use identical material for the microprobe analyses, the lithium- and H20-determ ination. As the measured boron content was unusually high and the silicon content was unusually low for a tourm aline, the microprobe analyses were repeated Table 1. Chemical composition o f olenite from the Koralpe (in wt. %). E.s.d. s in parentheses (Analyst: H.-J. Bernhardt) S i (19) T i (2) B2O (31) A (10) FeO 0.05 (2) MnO 0.01 (2) MgO 0.01 (1) CaO 1.47 (3) NaaO 1.46(3) 1.46 k 2o 0.02 (1) Li ( - ) F 0.11 (2) h 2o 3.25 ( - ) Total Number o f ions on the basis o f 31 (O, OH, F) Si B * B Al Al Mg Ti Li Fe Mn Na Ca K OH F Mean o f ten microprobe analyses (for Li and H20 see text) 2 Theoretical olenite, NaAljAlf^BO^^SiftOi^C^OH). (cf. S o k o lo v et al. 1986) 3 Theoretical alkali- and alkali-earth-free Al-tourm aline A ^ A l^ B O.-j^ SiftO ^ C ^O H ^ * For the excess o f ions at this position ( Si and B) see Experimental, this work. 6 A. E r t l et a l. Akademie d. Wissenschaften Wien; download unter several times. No significant changes were noticed. The totals of the analyses were slightly too high (see Table 1). Microprobe analyses of boron may be inaccurate owing to several factors (B astin and H e ijlig e r s, 1986, M cg ee and A n o v it z, 1996). Assuming that only for boron the obtained value was too high, its analytical value may be reduced to an amount to reach a sum of constituents of 100%. Even then the boron content is still too high for a normal olenite. A partial substitution of Si by B in natural tourmalines was proposed by B arton (1969) and by S e r d y u c h e n k o (1980) previously, but only on the basis of chemical analyses, and not corroborated by structure determinations. The quality of the crystal used for structure refinement was checked by film methods (Weissenberg type), using Cu-Ka radiation. A detailed compilation about data collection and structure refinement is given in Table 2. Details o f crystal data, X-ray measurements, and structure determination Crystal system trigonal Space group R3m (160) Unit - cell dimension [A] a = (2) c= (2) Volume o f unit - cell [A3] (5) T (K ) 295 (2) Z 3 Dcaic [Mg.m 3] Dmcas [Mg.m-3 ] 3.02 (4) Cut crystal chip [mm3] 0.20 x 0.50 x 0.20 Diffraktometer Stoe AED 2 Radiation M o K a (A = A) Linear absorption coefficient [mm- 1 ] 1.34 Scan mode (0 2 0 Measured reflections 7630 Independent reflections 1443 Rjnt Reflections with Fo 4 a (Fo) 1443 Range o f h k l ±h, ± k, 1 Max 2 0 value [ ] 80 Absorption correction 'I'-scan data Transmission factors 0.25 to 0.20 Refinement on F2 Number o f variables 100 R(F), 1443 data Rw(F2), 1443 data w = l/[p2(fo2)+(0.59.p)2] P=[max(Fo2,0)+ 2.Fc2]/3 Extinction coefficient (4) Max A/cr Final difference Fourier summation [e.ä3] 0.43 to Akademie d. Wissenschaften Wien; download unter Table 3. Structural parameters with e.s.d. s in parentheses.the anisotropic displacement factors are defined as exp ( 27T2E jsj Uij hi hj a* i a*j); [A X 104]. Wyck: number of positions and Wyckoff notation, sof: occupation factors Atom Wyck x y z sof u /uiso u 22 U33 U23 U13 UI2 Na 3a (2) 0.07 (2) 240 (10) Uu 205 (11) 0 0 1/2 U Ca 3a (2) 0.05 (1) 240 (10) U 205 (11) 0 0 1/2U AI (1) 9b (2) (3) (8) (1) 90(1) 98 (2) 127 (2) 20 (1) 1/2 U2, 1/2 U22 Li (1) 9b (2) (3) (8) (1) 90(1) 98 (2) 127 (2) 20 (1) 1/2 U 1/2 U27 Al (2) 18c (2) (2) (4) (3) 100(1) 112(1) 87(1) 6(1) - 8 ( 1 ) 54(1) Li (2) 18c (2) (2) (4) (3) 100(1) 112(1) 87(1) 6(1) - 8 ( 1 ) 54(1) Si 18c (2) (2) (4) (3) 96(1) 89(1) 86(1) - 7 ( 1 ) 1(1) 37(1) B (1) 18c (2) (2) (4) (3) 96(1) 89(1) 86(1) - 7 ( 1 ) 1(1) 37(1) 0 ( 1 ) 9b (3) (7) (17) (3) 92 (3) 165 (4) 13(3) 1/2 U23 1/2 U22 0 ( 2 ) 9b (4) (8) (16) (2) 197 (4) 136 (4) (3) 1/2 U2, 1/2 U22 0 ( 3 ) 9b (4) (8) (14) (2) 233 (4) 99 (3) 11 (3) V2 U23 1/2 U2, 9b (4) (9) (16) (2) 227 (4) 128 (4) -5 ( 3 ) 1/2 U 1/2 U 18c (4) (4) (10) (2) 111 (2) 101 (2) - 2 ( 2 ) 4(2) 43(2) 0 ( 6 ) 18c (4) (4) (9) (2) - 8 ( 2 ) 12(2) 42(2) 18c (4) (5) (10) (2) 116 (2) 32 (2) 1 53(2) 0,F 3a (3) (4) Un 147 (2) 0 0 1/2 U B 9b (4) (9) (19) (3) 94(4) 103 (4) 6(3) 1/2 U?3 1/2 U H 9b 0.794(1) (3) (8) (11) Investigations on Olenite with Excess Boron from the Koralpe, Styria, Austria Akademie d. Wissenschaften Wien; download unter 00 Table 4. Selected interatomic distances and some mean values [Ä ] as well as bond angles [ ], E.s.d. s in parentheses Na - 0 (1) 0,F (2); 3x (1); 3x (1); 3x 3.13; lx Al (1) 0,F 0 (1) 0 ( 3 ) 1.898(1); lx (1); 2x (1); 2x (1); lx Si - 0 (6) Al (2) 1.600(1) (1) (1) (1) 0 (6) 0 ( 7 ) 0 (6 ) 0 ( 3 ) 0 (6) (1) 1.880(1) 1.883(1) 1.892(1) (1) (1) Si Si (3) (5) (5) (5) (5) (6) A. E rtl et a l. B - 0 (1) (2); (1); lx 2x 0 (1) (5); 2x (10); lx 1.372 Investigations Akademie on Olenite d. Wissenschaften with Excess Wien; Boron download from unter the Koralpe, Styria, Austria 9 Table 2. In all calculations complex neutral scattering functions were used and the Lorentz and polarization effects were corrected in usual ways. ( Fo - 1Fc ) lists are deposited at the Institut für Mineralogie und Kristallographie der Universität Wien. The refined atomic parameters and anisotropic displacement factors are given in Table 3, selected interatomic distances and bond angles in Table 4. The sum of occupation factors for positions Al(l)/Li(l), Al(2)/Li(2), and Si/B(l) are constrained constant with multiplicity 0.5,1.0 and 1.0 respectively, for position Na/Ca they are unconditionally free variables. Discussion The combined results of chemical analyses and X-ray investigations of the tourmaline under discussion with the formula (Nao.43 Cao.24Go.33XAl2.43 I-io.33Go.28)Al6(B03)3(B1 23 Si4.8? Oi8)[C*o.64(OH)3 36] convincingly show (contrary to the preliminary note by E rtl 1995). a) that the X position is partly occupied by Na and Ca (and by traces of K) atoms, and b) that the Si position contains appreciable amounts of B. The ratio B/Si calculated from chemical analyses with ~ 0.25 differs considerably from the ratio determined by the X-ray work with ~ The reason for this discrepancy might be an analytical error in the B determination (too high values) by microprobe analyses already mentioned above. Further it seems to be worth mentioning that from diagrams where the (Si-O) bond length [A] is plotted against the Si content [apfu = atoms per formula unit] (H aw t h o rn e 1996,1997) for our experimental ((Si, B )-0) = 1.610Ä a value of ~ 5.70 Si [apfu] is deducible. Our chemical analyses as well as the least squares refinement of the occupancy (Table 3) indicate for Si [apfu] a value The reasons for this discrepancy between (Si-O) [Ä] and Si [apfu] are not clear, but our experimental values for Si [apfu] 5.25 and (Si-O) = 1.610Ä seem to be well established. Vacancies and partial Al substitution of Si-position cannot be excluded by the X-ray work. Acknowledgements The authors thank Dr. P. Schmitzer, Graz, Austria, for providing the sample as well as Prof. Dr. J. Zemann and Dr. G. Giester for many helpful discussions concerning the tourmaline structure type. 10 A. E rti Akademie. et a l.: Investigations d. Wissenschaften Wien; on download O lenite unter w ith Excess B oron References B a r t o n R. Jr., 1969: Refinement o f the crystal structure o f buergerite and the absolute orientation o f tourmalines. - Acta Cryst. B 25, B a s itn, G. F, and H kiji.igkrs, H. J. M., 1986: Quantitative electron probe microanalyses of boron in binary borides. -University o f Technology, publ. o f the Lab. forphys. Chem. 115p. E r ti. A., 1995: Elbait, Olenit, Dravit-Buergerit-Mischkristalle, Dravit, Uvit und ein neuer Al-Turmalin(?) von österreichischen Fundstellen. Mitt. Österr. Miner. Ges 140, Haw n iorn i:, F. C., 1996: Structural mechanisms for light-element variations in tourmaline. Canad. Mineral.Vol. 34, H a w tiio rn i-, F. C., 1997: The crystal chemistry of tourmaline: current status. Tourmaline 1997 International Symposion on Tourmaline. Abstracts, McGi-i;, J. J. and A n o v i t z, L. M., 1996: Microprobe Analysis ofgeological Materials. In: G riiw, Fl. S. and A n o v itz. L. M., (1996): Boron Mineralogy, Petrology and Geochem istry, Rev. in Mineralogy, 33, N ik d k r m a y r, G., M o s k r, B., P osti., W., a n d W a i.ti.r, F., 1986: N eu e M in e r a lfu n d e aus Ö ste rre ic h X X X V. C a rin th ia II, 176./96., PosTi.,W., 1988: Neue imineralfunde in der Steiermark. Mitt. Österr. Miner. Ges. 133,7 11. P osti., W., and M o s k r, B., 1987: Ein Turmalinpegmatit östlich der Stoffhütte, Koralpe, Steiermark. Mitt. Abt. Miner. Landesmuseum Joanneum, 55, S k r d y ic iik n k o, D. P., 1980: Different positions o f boron in tourmaline lattices. Dokl. Akad. Sei. USSR 254, (in Russian). SoKOLcn; P. B., G o r s k a y a, M. G., G o rd ii:n k o, V. V, P k tk o v M. G., K r k t s k r, Yu. L., F ra n k - K a m i- n ts k ii, V. A., 1986: Olenit Na! xa ly\ l6b3si60 27(0, ()H)4 a new highaluminous mineral o f the tourmaline group. Zapiski Vses. Mineralog. Obshch 115, (in Russian). Authors addresses: A. E r t i. and Prof. Dr. F. P k r tl.ik, Institut für Mineralogie und K ristallographie, Geozentrum Universität W ien, Althanstraße 14, A-1090 Wien, Austria; Dr. H-J. B e r n h a r d t, Z. Elektronen-Mikrosonde der RUB, Ruhr-Universität Bochum, D Bochum, Germany.
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