ConchoidalArthur Thomas, Gemstones (2009)
Uneven, Subconchoidal, Uneven, Subconchoidal, Splintery, UnevenArthur Thomas, Gemstones (2009)
Tourmaline is a series of several different minerals with unique chemical formulas.
Al 2SiO 5Michael OâDonoghue , Gems, Sixth edition (2006) More from other references