Gems, Conchoidal, Brittle
ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Ca 3Ti4+2(Fe3+2Si)O 12Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Be 2BO 3(OH)Ulrich Henn and Claudio C.