Original paper
Synthesis and crystal structure of Ga-rich, Fe-bearing tourmaline
Vereshchagin, Oleg S.; Setkova, Tatiana V.; Rozhdestvenskaya, Ira V.; Frank-Kamenetskaya, Olga V.; Deyneko, Dina V.; Pokholok, Konstantin V.
European Journal of Mineralogy Volume 28 Number 3 (2016), p. 593 - 599
published: Sep 23, 2016
Abstract
Crystals of Ga-rich, Fe-bearing tourmaline (~25 wt% Ga2 O3, 11 wt% FeOtotal) were grown from hydrothermal solution at 100 MPa and 600°C. The crystals were grown on a seed as a newly formed, up to 200 μm thick layer and, in addition, as free, spontaneously nucleated elongated prisms, 10 to 200 μm in size. The crystal structure of the synthetic tourmaline was studied by Mössbauer spectroscopy and single-crystal X-ray diffraction (to an R -index of 0.032; a = 16.000(1), c = 7.257(1) Å). Gallium and iron cations are distributed over the Y and Z octahedral sites according to the crystal-chemical formula (Na0.95|0.05) (Ga1.34 Fe2+ 0.62Al0.44Fe3+ 0.34Ni0.26) (Al3.28Ga 1.92Fe2+ 0.41Fe3+ 0.39) (Si6O18) (BO 3)3(OH2.29O0.71) (O), suggesting that the disordered distribution previously shown for Al3+ also holds for other trivalent cations in tourmalines.
Keywords
crystal structure • tourmaline • gallium • mössbauer spectroscopy • synthesis • x-ray single-crystal analysis