I believe you have to rub two very specific materials together to produce sparks to make fire. One of the materials has to be flint, a kind of mineral quartz, and the other material has to contain iron (it could be some other kind of rock or steel). When we strike flint quickly across the iron-containing material, it exposes fresh un-oxidized iron and the friction induced by the action results in heating of the material above its ignition temperature. If oxygen is present (which it is in the atmosphere), then this produces sparks. These sparks can be used to ignite tinder to get a fire going.