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