Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
Uneven, Uneven, Management Team (2012), Conchoidal, Brittle
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references
Fe 3O 4Ulrich Henn and Claudio C.