Rust is the name given to a collection of iron oxides. You'll find rust in all situations where unprotected iron or steel is exposed to the elements. Did you know rust comes in colors besides red? There is brown, orange, yellow and even green rust! Green rust is an unstable corrosion product typically produced in a low-oxygen environment, such as rebar in the chlorine-rich environment of seawater, which may result in [FeII3
, a series of iron hydroxides. Depassivation of steel to form green rust occurs when the ratio of concentration of chloride ions to hydroxide ions is greater than 1. Therefore, rebar in concrete, for example, may be protected from green rust if the alkalinity of the concrete is high enough.
There is a natural mineral which is the equivalent to green rust called fougerite. Fougerite is a blue-green to blue-gray clay mineral found in certain wooded regions of France. The iron hydroxide is believed to give rise to other related minerals.
Have you ever seen green rust? Which colors of rust have you encountered?