Altogether there are sixteen known iron oxides and oxyhydroxides.

Oxides

• wüstite (FeO)
• magnetite (Fe₃O₄)
• hematite (α-Fe₂O₃), β-Fe₂O₃,
• maghemite (γ-Fe₂O₃), ε-Fe₂O₃

Hydroxides

• iron(II) hydroxide (Fe(OH)₂)
• iron(III) hydroxide (Fe(OH)₃, (bernalite)

Oxide-hydroxides

• goethite (α-FeOOH),
• akaganéite (β-FeOOH),
• lepidocrocite (γ-FeOOH),
• feroxyhyte (δ-FeOOH),
• ferrihydrite (Fe₅HO₈·4H₂O)
• high-pressure FeOOH
• schwertmannite
• green rusts

Uses

Some of these oxides are used in ceramic applications, particularly in glazing. Many metal oxides provide the colours in glazes after being fired at high temperatures.

Iron oxides yield pigments (see Iron oxide pigments) that are widely used in the cosmetic field. They are considered to be nontoxic, moisture resistant, and nonbleeding. Iron oxides graded safe for cosmetic use are produced synthetically in order to avoid the inclusion of ferrous or ferric oxides, and impurities normally found in naturally occurring iron oxides.

Magnetite (under the name Black Oxide) is used for coating steel tools . This protects them from corrosion and gives a pleasing appearance.

Properties

• Iron(II) oxide (FeO) or ferrous oxide is also known as wüstite in its mineral form. As a powder this black oxide can cause explosions as it readily ignites.

• Iron(III) oxide (Fe₂O₃) or ferric oxide is also known as hematite (alpha form) or maghemite (gamma form) in its mineral form. As an industrial chemical it is commonly called rouge. Purified, it is used as a coating in magnetic audio and computer media. In a dry or alkaline environment it can cause passivation and inhibits rust, yet it is also a major component of rust.

• Iron(II,III) oxide (Fe₃O₄) or ferrous ferric oxide is also known as magnetite or lodestone in its mineral form, a major iron ore. Magnetite forms readily when iron oxidizes underwater, and so is often found inside tanks or below the waterline of ships.

It is not difficult to extract iron from ore as compared to the similarly abundant elements aluminum and titanium.

References

1. ^ Cornell, RM; Schwertmann, U (2003). The iron oxides: structure, properties, reactions, occurrences and uses. Wiley VCH. ISBN 3-527-30274-3. 
2. ^ http://www.epi.com/black-oxide/blackoxide-faq.htm