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