The Collaborative International Dictionary of English v.0.48:

Pyrite \Pyr"ite\, n.; pl. Pyrites. [Cf. F. pyrite. See
   Pyrites.] (Min.)
   A common mineral of a pale brass-yellow color and brilliant
   metallic luster, crystallizing in the isometric system; iron
   pyrites; iron disulphide.
   [1913 Webster]

         Hence sable coal his massy couch extends,
         And stars of gold the sparkling pyrite blends. --E.
                                                  Darwin.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pyrites \Py*ri"tes\, n. [L., fr. Gr. ?, fr. ? fire. See Pyre.]
   (Min.)
   A name given to a number of metallic minerals, sulphides of
   iron, copper, cobalt, nickel, and tin, of a white or
   yellowish color.
   [1913 Webster]

   Note: The term was originally applied to the mineral pyrite,
         or iron pyrites, in allusion to its giving sparks when
         struck with steel.
         [1913 Webster]

   Arsenical pyrites, arsenopyrite.

   Auriferous pyrites. See under Auriferous.

   Capillary pyrites, millerite.

   Common pyrites, isometric iron disulphide; pyrite.

   Hair pyrites, millerite.

   Iron pyrites. See Pyrite.

   Magnetic pyrites, pyrrhotite.

   Tin pyrites, stannite.

   White iron pyrites, orthorhombic iron disulphide;
      marcasite. This includes cockscomb pyrites (a variety of
      marcasite, named in allusion to its form), spear pyrites,
      etc.

   Yellow pyrites, or Copper pyrites, the sulphide of copper
      and iron; chalcopyrite.
      [1913 Webster] Pyritic

WordNet (r) 3.0 (2006):

pyrites
    n 1: any of various metallic-looking sulfides (of which pyrite
         is the commonest)