ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
ZrSiO 4Michael OâDonoghue , Gems, Sixth Edition (2006)
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.