Conchoidal, Metallic, UnevenArthur Thomas, Gemstones (2009), Brittle, Conchoidal
Uneven, Uneven, Gems, Sixth Edition (2006)
Cu 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Al 2O 3Michael OâDonoghue , Gems, Sixth Edition (2006)