ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, Uneven, Gems, Sixth Edition (2006)
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
KAlSi 3O 8Michael OâDonoghue , Gems, Sixth Edition (2006)