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ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Uneven
Ca 2(Mg,Fe,Mn,Al) 2(SiO 4)(Si 2O 7)(OH) 2 · H 2OUlrich Henn and Claudio C.
Mg 3Al 6(Si,Al,B) 5O 21(OH)Walter Schumann , Gemstones of the world (2001) More from other references