Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Gemstones (2009), Flexible Flexible fragments.
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.
Al 2Si 4O 10(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references