Conchoidal, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle, Metallic
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
PbCa 3Zn 4(SiO 4) 4Anthony 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.