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