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