D defs.my
Entry 2 senses Webster, 1913

Firestone

/fīr'-stōnˌ/ · Fire·stone · IPA /fˈaɪrstˌoʊn/
01 n. Iron pyrites, formerly used for striking fire; also, a flint.
  1. 1.
    Iron pyrites, formerly used for striking fire; also, a flint.
  2. 2.
    A stone which will bear the heat of a furnace without injury; -- especially applied to the sandstone at the top of the upper greensand in the south of England, used for lining kilns and furnaces.