A nonmetallic element of the sulphur group, and analogous
   to sulphur in its compounds. It is found in small quantities with
   sulphur and some sulphur ores, and obtained in the free state as a dark
   reddish powder or crystalline mass, or as a dark metallic-looking
   substance. It exhibits under the action of light a remarkable variation
   in electric conductivity, and is used in certain electric apparatus.
   Symbol Se. Atomic weight 78.9.