As a youngster, I recall a neighbor had several rocks that were white with large areas of darker stone I now know as flint. Were the white portions limestone? I suppose even by then I was aware if you strike flint with steel, you get sparks. The reader may find online more than one explanation of why striking steel against flint produces sparks. Frankly, not all of the explanations provided are completely accurate. The best explanation is also the one that is most logical, most reasonable.
Chip Off the Old Block
Freshly broken flint, while somewhat smooth to the eye, if examined microscopically, has a rough surface. Now flint, would you believe it, is actually harder than steel. So what is the mechanism whereby one get sparks from steel and flint?
Steel and Flint
When a piece of steel is dragged quickly across a fresh flint surface, very tiny pieces of metal are heated by the friction to a temperature above the ignition point for iron. Iron is the main component of steel. In the presence of oxygen, the steel particle burns at white heat to produce a brilliant spark and a burned out cinder!
Does this not seem reasonable to you? Then consider this. Still smaller pieces of iron do not even need friction to ignite them in oxygen. Such iron is said to be pyrophoric. The video embedded below, affords visual proof that the above explanation is not only reasonable, but true as well.
Note: You might also enjoy Differences Between Fluorescence, Phosphorescence, Incandescence
- Northern Illinois University: Flint and Steel Firebuilding
- Ragweed Forge: Firemaking with Flint and Steel
- Microscopic Observations, by Robert Hooke (1780)