ConchoidalArthur Thomas, Gemstones (2009)
Uneven, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Tourmaline is a series of several different minerals with unique chemical formulas.
(Mg,Fe) 5(SiO 4) 2(F,OH) 2Ulrich Henn and Claudio C.