firestone

n. [ AS. f&ymacr_;rstān flint; f&ymacr_;r fire + stān stone. ] 1. Iron pyrites, formerly used for striking fire; also, a flint. [ 1913 Webster ]

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. Ure. [ 1913 Webster ]