Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Uneven, Gemstones (2009), Splintery
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.
Ca 2NaHSi 3O 9Ulrich Henn and Claudio C.