Almost everyone has seen a movie character start a fire using a piece of flint, but you may wonder how this is possible. Flint is a hard stone that can produce sparks when it is struck against a metal, such as steel. The sharp edge of the flint breaks off a small splinter of steel, which is heated significantly by the friction from the strike of the flint. As this splinter of hot steel reacts with oxygen in the air, a spark is produced. The sparks generated in this way can then ignite a piece of dry wood, paper, or other fuel.