Uneven, Splintery, Conchoidal, Uneven, Splintery, Conchoidal, UnevenWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009)
SiO 2Arthur Thomas , Gemstones (2009)
Tourmaline is a series of several different minerals with unique chemical formulas.