ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Uneven, Uneven, Gems, Sixth Edition (2006)
Perfect on {010}, good on {100}
Perfect [001] good [010] poor [110]
Be 2BO 3(OH)Ulrich Henn and Claudio C.
CaAl 2Si 2O 8Michael OâDonoghue , Gems, Sixth Edition (2006)