Gemstones of the world (2001)
Conchoidal, Brittle, Conchoidal, Brittle, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
SiO 2Walter Schumann , Gemstones of the world (2001)
PbSO 4Michael OâDonoghue , Gems, Sixth edition (2006) More from other references