ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Be 2BO 3(OH)Ulrich Henn and Claudio C.
Na 3(Na,K)Al 4Si 4O 16Ulrich Henn and Claudio C.