Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Subconchoidal, Uneven, Conchoidal, Uneven
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.
Mn2+ Al(PO 4)(OH) 2H 2OMichael OâDonoghue , Gems, Sixth Edition (2006)