Conchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Brittle, Metallic
Uneven, Uneven, Gems, Sixth Edition (2006)
CaBSiO 4(OH)Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Al 2O 3Michael OâDonoghue , Gems, Sixth Edition (2006)