UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
NaCa 2Al 5Si 5O 20 · 6H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.