The iron ore deposits are found in sedimentary rocks. They are formed by the chemical reaction of iron and oxygen mixed in the marine and fresh water. The important iron oxides in these deposits are hematite and magnetite. These are ores from where iron is extracted.
Iron ore formation
The iron ore formation started over 1.8 billion years ago when abundant iron was dissolved in the ocean water which then needed oxygen to make hematite and magnetite. The oxygen was provided when the first organism capable of photosynthesis began releasing oxygen into the waters. This oxygen combined with dissolved iron to form hematite and magnetite. These then deposited on the ocean floor abundantly which are now known as banded iron formation.
Iron is extracted from the iron ore which is then used in steel and other ironic things.