Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001)
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references
(Zn,Mn2+ ,Fe2+ )(Fe3+ ,Mn3+ ) 2O 4Anthony et al , Handbook of mineralogy (2001)