ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
SiO 2Walter Schumann , Gemstones of the world (2001)
Al 2(PO 4)(OH) 3Michael OâDonoghue , Gems, Sixth Edition (2006)