Uneven, Conchoidal, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle
Uneven, Uneven, Gems, Sixth Edition (2006)
FeS 2Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Al 2O 3Michael OâDonoghue , Gems, Sixth Edition (2006)