firestone

1. Iron pyrite, formerly used for striking fire. (countable, uncountable)
2. A flint. (countable, uncountable)
3. A heat-resistant stone that will withstand intense heat of a furnace, used for lining kilns, campfire rings, fireplaces and furnaces; especially, the sandstone at the top of the upper greensand in the south of England. (countable, uncountable)

الجمع firestones