Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Uneven, Uneven, ConchoidalAnthony 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.
Ca 5(PO 4) 3FAnthony et al , Handbook of mineralogy (2001)