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Definition of TOURMALINE

  • A brittle gray or black mineral that occurs as prismatic crystals in granitic and other rocks. It consists of a boron aluminosilicate and has pyroelectric and polarizing properties, and is used in electrical and optical instruments and as a gemstone
  • (French) a brittle boron aluminosilicate mineral with a glassy lustre, occurring as prismatic crystals of the trigonal system [n -S]