Uneven, Uneven, Gems, Sixth Edition (2006), Uneven, Conchoidal
Uneven, Splintery, Conchoidal, Uneven, Splintery, Conchoidal, UnevenWalter Schumann, Gemstones of the world (2001)
NaAlSi 3O 8Michael OâDonoghue , Gems, Sixth Edition (2006)
SiO 2Arthur Thomas , Gemstones (2009)