Brittle, Metallic, Brittle, Metallic
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle, Metallic
Ca(Mg,Al)3(Al3Si)O10(OH)2
BeAlSiO 4(OH)Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references