ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
ConchoidalArthur Thomas, Gemstones (2009)
CaZrBAl 9O 18Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Tourmaline is a series of several different minerals with unique chemical formulas.