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