ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Conchoidal, Metallic, UnevenArthur Thomas, Gemstones (2009), Brittle, Conchoidal
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
Cu 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references