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