UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
Subconchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Irregular
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.
SnO 2Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references