TETRAHEDRALLY COORDINATED BORON IN A TOURMALINE: BORON-RICH OLENITE FROM STOFFHUTTE, KORALPE, AUSTRIA

Abstract

The substitution of [4] B for [4] Si in tourmaline has been the source of much discussion.A sample of olenite from Stoffhütte, Koralpe, Styria, Austria has been found to contain more than one [4] B per formula unit of 31 (O,OH,F), demonstrating that significant [4] B = [4] Si substitution does indeed occur in tourmaline.The composition of the structurally characterized crystal was determined using electron microprobe and SIMS data; in combination with refinement of the site scattering, the chemical data yield an optimized formula of Y (Na 0.400 Ca 0.294 Ⅺ 0.306 ) Z (Al 2.424 Li 0.357 Ⅺ 0.219 ) (Al 5.916 Ⅺ 0.084 ) B 3.00 (Si 4.854 B 1.062 Al 0.084 ) ⌺6.00 O 27 [F 0.06 (OH) 3.31 O 0.63 ].The Austrian olenite crystallizes in space group R3m, a 15.731(3), c 7.0638(9) Å.The atomic arrangement was refined to R = 0.014 using X-ray data; <T-O> is equal to 1.609 Å, reflecting substitution of the smaller boron atom for Si.Conjecture on the pattern of distribution of [4] B can be made on the basis of X-site occupancy.