Splintery, UnevenArthur Thomas, Difficult, Fibrous
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle, Metallic
NaAlSi 2O 6Ulrich Henn and Claudio C.
BeAlSiO 4(OH)Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references