\Tour"ma*line\, n. [F. tourmaline, cf. It. turmalina,
tormalina, NL. turmalina, turmalinus; all fr. tournamal, a
name given to this stone in Ceylon.] (Min.)
A mineral occurring usually in three-sided or six-sided
prisms terminated by rhombohedral or scalenohedral planes.
Black tourmaline (schorl) is the most common variety, but
there are also other varieties, as the blue (indicolite), red
(rubellite), also green, brown, and white. The red and green
varieties when transparent are valued as jewels. [Written
also {turmaline} .]

Note: Crystals of tourmaline when heated exhibit electric
      polarity (see {Pyroelectric}, n.). Tourmaline is also
      used in the form of a polariscope called tourmaline
      tongs.