ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
Be 2BO 3(OH)Ulrich Henn and Claudio C.
Na 2(Ti,Fe)Si 4(O,F) 11Ulrich Henn and Claudio C.