Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Uneven, UnevenAnthony et al, Handbook of mineralogy (2001)
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.
Pb 5Cu 2(SO 4) 3(CO 3)(OH) 6Anthony et al , Handbook of mineralogy (2001)