Green rust is a generic name for various green crystalline chemical compounds containing iron(II) and iron(III) cations, the hydroxide () anion, and another anion such as carbonate (), chloride (), or sulfate (), in a layered double hydroxide structure. The most studied varieties are
* carbonate green rust – GR(): [()] · [·2].
* chloride green rust – GR(): [()] · [·n].
* sulfate green rust – GR(): [()] · [·2].
Other varieties reported in the literature are bromide , fluoride , iodide , nitrate , and selenate.
Green rust was first recognized as a corrosion crust on iron and steel surfaces. It occurs in nature as the mineral fougerite.