Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Irregular/uneven, Brittle, Metallic
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.
Ca6(Al,Si)2(SO4)2B(OH)4(OH,O)12•26(H2O)