UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.
ZrO 2Arthur Thomas , Gemstones (2009)