What many people do not realize is that iron is a pyrophoric material; in the presence of oxygen, iron catches on fire automatically! It just starts burning. “But how can this be?” you may ask. “I can hold a chunk of iron in my hand and it does not burn me”.

The answer lays in the fact that the portion of the iron object in contact with the air and your skin is not pure iron. Rather it has developed a thin coating of iron oxide, or rust, immediately upon contact with the oxygen in the air. This serves to seal off the iron inside from exposure to the air and reduces the rate of further rusting.

Iron, whether man-made objects or naturally occurring in rocks, will rust upon exposure to oxygen in the air. The act of rusting is actually an exothermic reaction called “oxidation”, which is a fancy way of saying when iron touches the oxygen in the air a reaction occurs; the iron rusts (turns into iron oxide) and gives off heat. In other words, it burns. The simplified chemical reaction can be expressed as:

Fe2 + O2 = Fe2O3 + heat

Or in English:

Iron + Oxygen = Rust + Heat