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