A new polytype of taaffeite–a rare beryllium mineral from the granulites of central Australia

Abstract

Summary: Chemical and single crystal X-ray studies have shown the existence of a 9-layer polytype of taaffeite. The parameters of the hexagonal unit-cell are a 5·675 Å, c 41·096 Å (a_rh 14·085 Å, α 23·24°). The oxide composition of the mineral is Al₂O₃ 71·44, MgO 15·76, FeO 6·78, BeO 5·50%. It is pale olive green, with refractive indices ω = 1·739, ε = 1·735, and a specific gravity of 3·68.