ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
ZrO 2Arthur Thomas , Gemstones (2009)
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.