Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Conchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.
(Cs,Na)(AlSi 2O 6) · 0.5H 2OWalter Schumann , Gemstones of the world (2001) More from other references