Gems, Sixth Edition (2006)
ConchoidalAnthony et al, Handbook of mineralogy (2001), ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle, Conchoidal
SiO2 (with a high level of nickel impurities )
CaBe 2(PO 4) 2Michael OâDonoghue , Gems, Sixth Edition (2006)