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UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
SiO 2Walter Schumann , Gemstones of the world (2001)
(Fe2+ ,Mg,Mn2+ ) 3(PO 4) 2 · 4H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references