Uneven, Uneven, Gemstones of the world (2001) More from other references
UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
Ca 10Mg 2Al 4(SiO 4) 5(Si 2O 7) 2(OH) 4Ulrich Henn and Claudio C.
(Fe,Mn) 7Si 7O 21Ulrich Henn and Claudio C.