Uneven, Brittle, Metallic, Gemstones (2009)
ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Na 2[Al 2Si 3O 10] · 2H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Be 2BO 3(OH)Ulrich Henn and Claudio C.