Iron(III) oxide-hydroxide

A number of species are dubbed iron(III) oxide-hydroxide. These chemicals are oxide-hydroxides of iron, and may occur in anhydrous (IronOxygen(Hydroxide)) or hydrated (IronOxygen(Hydroxide)·nH₂O) forms. The monohydrate(IronOxygen(Hydroxide)·H₂O) might otherwise be described as iron(III) hydroxide (Iron(Hydroxide)₃), and is also known as hydrated iron oxide or yellow iron oxide.

Iron(III) oxide-hydroxide occurs naturally as the minerals goethite (CAS numberCASREF|CAS=20344-49-4), akaganéite (rarely found in weathered meteorites), lepidocrocite and feroxyhyte, as well as siderogel and limonite, which is a commonly found mixture of mainly goethite, lepidocrocite, quartz and clay minerals. Goethite and lepidocrocite, both crystallizing in orthorhombic system, are the most common forms of iron(III) oxide-hydroxide and the most important mineral carriers of iron in soils. The mineral ferrihydrite, also a soil constituent, is a related compound.

Yellow iron oxide (CAS CASREF|CAS=51274-00-1) is used as a pigment, eg. Pigment Yellow 42 or C.I. 77492. Pigment Yellow 42 is Food and Drug Administration (FDA) approved for use in cosmetics and is used in some tattoo inks. Solid material color ranges from yellow through dark brown to black. Its risk and safety phrases are R36 R37 R38 S26 S36.

Iron oxide-hydroxide is used in aquarium water treatment as a phosphate binder. [http://www.reefkeeping.com/issues/2004-11/rhf/index.php]

ee also

*Iron pillar of Delhi
*bernalite

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