UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Na 8Al 6Si 6O 24Cl 2Michael 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.