Gems, Sixth Edition (2006)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
SiO2 (with a high level of nickel impurities )
MgAlBO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references