Conchoidal, Brittle, Conchoidal, UnevenArthur Thomas, Gemstones (2009), Brittle, Conchoidal
UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
CaSO 4Michael OâDonoghue , Gems, Sixth edition (2006) More from other references
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.