Uneven, Brittle, Uneven, Brittle, Uneven
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle, Metallic
(K,Na)Ca4Si8O20(F,OH)•8(H2O)
BeAlSiO 4(OH)Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references