Firestone
Firestone (?; 110) , noun
[Anglo-Saxon fȳrstān flint; fȳr fire + stān stone.]
1.
Iron pyrites, formerly used for striking fire; also, a flint.
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