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