ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Splintery
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Na 4Al 3Si 9O 24Cl to Ca 4Al 6Si 6O 24(CO 3,SO 4)Walter Schumann , Gemstones of the world (2001) More from other references
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.