Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Na 3(Na,K)Al 4Si 4O 16Ulrich Henn and Claudio C.
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.