ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, Uneven, Gems, Sixth Edition (2006)
SiO 2Ulrich Henn and Claudio C.
CaAl 2Si 2O 8Michael OâDonoghue , Gems, Sixth Edition (2006)