By virtue of this high spin d5 electronic configuration, these ions are paramagnetic and are weak chromophores.

The actual identity of the iron species is often vague, but many applications do not demand high purity materials.

It is produced on a large scale by treating sulfuric acid, a hot solution of ferrous sulfate, and an oxidizing agent.

Typical oxidizing agents include chlorine, nitric acid, and hydrogen peroxide.

All the mentioned natural hydrates are unstable connected with the weathering (aerobic oxidation) of Fe-bearing primary minerals (mainly pyrite and marcasite).