Tetrahedrally coordinated boron in a tourmaline: Boron-rich olenite from Stoffhutte, Koralpe, Austria

The substitution of B-[4] for Si-[4] in tourmaline has been the source of m uch discussion. A sample of olenite from Stoffhutte, Koralpe, Styria, Austr ia has been found to contain more than one B-[4] per formula unit of 31 (O, OH,F), demonstrating that significant B-[4] = Si-[4] substitution does inde ed occur in tourmaline. The composition of the structurally characterized c rystal was determined using electron microprobe and SIMS data; in combinati on with refinement of the site scattering, the chemical data yield an optim ized formula of (Y)(Na(0.400)Ca(0.294)square (0.306)) (Z)(Al(2.424)Li(0.357 )square (0.219)) (Al(5.916)square (0.084)) B-3.00 (Si4.854B1.062Al0.084)(Si gma6.00) O-27 [F-0.06(OH)(3.31)O-0.63]. The Austrian olenite crystallizes i n space group R3m, a 15.731(3), c 7.0638(9) Angstrom. The atomic arrangemen t was refined to R = 0.014 using X-ray data; <T-O> is equal to 1.609 Angstr om, reflecting substitution of the smaller boron atom for Si. Conjecture on the pattern of distribution of B-[4] can be made on the basis of X-site oc cupancy.