Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Conchoidal, Brittle
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.
(Mn2+ ,Fe2+ ,Mg)(Fe3+ ,Mn3+ ) 2O 4Anthony et al , Handbook of mineralogy (2001)