Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
KAlSi 2O 6Michael 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.