A fire striker is a piece of carbon steel from which sparks are struck by the sharp edge of flint, chert, or similar rock. It is a specific tool used in fire making. Before the invention of matches, percussion fire-making was often used to start fires. Before the advent of steel, a variety of iron pyrite or marcasite was used with flint and other stones to produce a high-temperature spark that could be used to create fire. When flint and steel were used, the fire steel was often kept in a metal tinderbox together with flint and tinder.

Source: Wikipedia