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