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