Conchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Ca 3Al 2(SiO 4) 3Arthur Thomas , Gemstones (2009)
Be 2BO 3(OH)Ulrich Henn and Claudio C.