What is Iron Oxide?

Iron is a metallic element with the chemical symbol Fe, and is one of the most prolific and commonly occurring mineral substances on Earth. Scientists estimate that is found in approximately 5% of the planet’s crust, and exists in its core, too. Iron turns to iron oxide when it comes into contact with oxygen, either on its own or in combination with other elements like water. When the mineral is exposed to water and air for extended periods of time it will usually produce rust, which is a reddish-brown oxide.

Deposits of iron oxide occur in the soil, too. Experts usually believe that these were created by the precipitation of iron from seawater during the Proterozoic Eon some 1.6 billion years ago. These deposits are found in locations around the world, though the greatest concentrations tend to be in what is now the United States, India, Australia, China, Brazil, and Russia.

Iron oxidizes a couple of different ways, and the results fall across a spectrum with some being mostly iron and others mostly oxygen. The ending color and technical specifications vary accordingly. There are two primary forms, known as (II) and (III), of the oxide in nature, though different elements and compounds sometimes draw from both sources. Rust, for example, is known as iron (II, III) oxide and has the chemical structure Fe₂O₃, though the (II, III) designation is also given to magnetite, a compound with the structure Fe₃O₄; a number of other compounds can also be included in this grouping. In most cases numerical designations say more about how the elemental iron and oxygen bind together than what the substance looks like.

Color matters, too. In most cases iron with heavy (II) concentrations tends to towards deep black and charcoal in color, while those with a (III) composition fall more on the reddish brown end of the spectrum. The planet Mars, for example, is often known as the “red planet” thanks to the high concentrations of iron (III) oxide on its crust and in its soil.

Among stable, room temperature elements, there are usually only three that are naturally magnetic, namely cobalt, nickel, and iron; among these, iron is usually the most magnetic, which manufacturers often capitalize on in the production of magnets, electronic parts, audio and video cassette tapes, and bank and magnetized credit cards. In these cases a bit of powdered oxide is combined with other elements and sealants to create magnetic tapes or bands that can be used to help keep working parts charged and in place. That the oxide occurs naturally in nature helps keep costs down, too.

The cosmetics industry uses the compound to create various pigments in make-up as well. Most oxide forms are non-toxic, water repellent, and do not run or bleed, making them an ideal additive to products like mascara, liquid and powder foundation, and eye shadow. Oxides can also be found in certain types of health products such as talcum powder, facial cream, and body cream. Some sunblock products contain it as well. Its structure is often thought to help block the sun’s harmful ultraviolet rays from damaging human skin.

In the art world, iron oxide is used to create pigments such as burnt sienna and burnt umber. Colors and paints made this way tend to be permanent and long lasting. Though the precise method of coloring paints has changed somewhat over time, the basic concept has been at play since the prehistoric age; the cave paintings at Lascaux, France, are just one example of how long this compound has been used and how well paints made with iron last. Modern manufacturers rarely rely on it alone to form base colors and pigment foundations, though it is often still an important ingredient.