UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Uneven
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
FeS 2Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.