Uneven, Conchoidal, Brittle
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle, Metallic
(Na,Ca)4-8Al6Si6(O,S)24(SO4,Cl)1-2
BeAlSiO 4(OH)Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references