ConchoidalArthur Thomas, Gemstones (2009)
Uneven, Conchoidal, Brittle, Metallic, ConchoidalArthur Thomas, Gemstones (2009)
Tourmaline is a series of several different minerals with unique chemical formulas.
Ca 3Cr 2(SiO 4) 3Ulrich Henn and Claudio C.