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