ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Be 3Al 2Si 6O 18Ulrich Henn and Claudio C.
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.