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