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