UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
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(Fe2+ ,Mg,Mn2+ ) 3(PO 4) 2 · 4H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Mn2+9(SiO 4) 4(OH,F) 2Anthony et al , Handbook of mineralogy (2001)