ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
ZrSiO 4Michael OâDonoghue , Gems, Sixth Edition (2006)
Be 2BO 3(OH)Ulrich Henn and Claudio C.