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ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
CuSiO 2(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)