According to Wikipedia, rust occurs when iron or its alloys corrode. Since I asked how does rust occur, and I already knew that answer, I decided to find an answer that I could call scientific.
Enter Wonderopolis, which explains it this way:
The surface of a piece of iron will begin to corrode first in the presence of oxygen and water. Given enough time, any piece of iron will change entirely into rust and disintegrate.
The process of rusting is a combustion reaction, similar to fire. Left in contact with oxygen, iron will react with the oxygen to form rust.
Thanks to Pinterest, I can show just what rust looks like.
And while I am sure that you've seen rust or have an idea of rust, I thought some of these rust-dyed fabrics would be of special interest.
And so, a few quilts...all with the beautiful colors that only rust can give. Well, fabric that is the color rust without the actual rust. Since rust causes fabrics to breakdown faster, this is an important distinction.