Uneven
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle, Metallic
MgB 3O 3(OH) 5 · 5H 2OMichael OâDonoghue , Gems, Sixth Edition (2006)
BeAlSiO 4(OH)Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references