Uneven, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
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(Mg,Fe) 5(SiO 4) 2(F,OH) 2Ulrich Henn and Claudio C.
H 4Mg 3Si 2O 9Walter Schumann , Gemstones of the world (2001) More from other references