Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references
(Fe,Mn) 7Si 7O 21Ulrich Henn and Claudio C.