Chemical Formula: Fe2O4
Color: Black or dark gray
Importance: Magnetite is one of the main sources of iron. Iron from magnetite is used to make steel and other fabricated metals. Is also naturally magnetic, which allows it to be made into magnets.
Other Interesting Information: Magnetite is the only naturally magnetic mineral. This makes it extremely easy to identify. All you have to do is hold a magnet to it and you will know if it is magnetite immediately.
My Take: Magnetite is really cool. Certain specimens are especially magnetic and are very strong. Also, magnetite tends to pull iron particles straight out of the air, forming a little fuzz of iron on the outside of the magnetite. No other mineral can do this.
For More Information: http://www.minerals.net/mineral/magnetite.aspx