Iron (III) hydroxide is the chemical compound, which is made of hydrogen, Iron, and oxygen having the chemical formula Fe(OH)3. Based on the hydration, crystal structure, and particle size and shape, the colour of the iron III hydroxides differ from dark-brown to black. Here we will study the Iron III hydroxide formula, its properties, chemical structure and uses. Ferric hydroxide formula is also Fe(OH)3.

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Iron III Hydroxide Properties

Chemical Name

Iron III Hydroxide

Other names

Ferric acid

Iron hydroxide formula or formula of ferric hydroxide


Melting Point

135 °C

Molar Mass

106.867 g/mol


4.25 g/cm³


Vivid dark orange crystals

Solubility in Water


Let us look at the other properties below.

The colour of Iron (III) oxyhydroxide ranges from yellow through dark-brown to black, based on the degree of hydration, particle shape, and size, and crystal structure.


The crystal structure of β-FeOOH (also called akaganeite) is that of BaMn8O16 or hollandite. The unit cell is tetragonal, having a=1.048 and c=0.3023 nm, and holds 8 formula units of FeOOH. Its dimensions are up to 500 × 50 × 50 nm. Often, twinning produces particles having the shape of hexagonal stars.


On heating Iron III Hydroxide, β-FeOOH decomposes and recrystallizes as α-Fe2O3 (which is called hematite).

Natural Occurrences

Anhydrous ferric hydroxide takes place in nature as the exceedingly rare mineral bernalite, Fe(OH)3·nH2O (n=0.0-0.25). Iron oxyhydroxides are also called FeOOH. They are more common and take place naturally as structurally various minerals (or polymorphs) and are denoted by the Greek letters α, β, γ, and δ.

Goethite with the chemical formula - α-FeO(OH) has been used as the ocher pigment since prehistoric times.

Feroxyhyte (δ) can be formed under the high-pressure conditions of the ocean and sea floors, being thermodynamically unstable with respect to the α-polymorph (or goethite) at the surface conditions.


Limonite, which is a mixture of different polymorphs and hydrates of ferric oxyhydroxide, is one of the three primary iron ores, having been used since 2500 BC, at least.

Yellow iron oxide, otherwise called Pigment Yellow 42, is the Food and Drug Administration - FDA approved for the usage in cosmetics and can be used in a few tattoo inks.

Also, iron oxide-hydroxide can be used in aquarium water treatment as a phosphate binder.

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The nanoparticles of iron oxide-hydroxide have been studied as possible adsorbents for the removal of lead from aquatic media.