Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.
Mg 3B 7O 13ClMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references