Why Is Some Dirt Red in Color?

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Minerals present in soil can alter its color.
Minerals present in soil can alter its color. (Image: Crackled soil image by Trombax from Fotolia.com)

Some dirt is reddish in color. This is due to the presence of certain materials in the soil. Red soils are often forested but can be unproductive; they need careful management if used for agriculture. However, some red soils offer superior growing conditions for certain crops. (See References 1, 2, 3 & 4.)

Iron Oxide

The different colors seen in soils are produced in them by the materials they contain. In red soils, the color is often due to a compound that is made when iron and oxygen react together, such as when metal is exposed to air and rusts. Tiny flecks of this compound, known as iron oxide, coat the particles of dirt so that the soil becomes red in color. (See References 1 & 2)

Iron oxide, when present in soil, can give it a reddish hue.
Iron oxide, when present in soil, can give it a reddish hue. (Image: rust image by Wolfgang Zintl from Fotolia.com)

Ultisoils

Although you can find red dirt in places where metal has been left to rust, red soils often occur naturally in the form of ultisoils. These are very old soils, held by experts to be the final product of weathering in certain climates where there is no new soil formation. (See References 2)

Examples

Examples of red soil can be found in Georgia red clay and the Terra Rossa soil that is found in various Mediterranean climates. In China's Dongchuan province, weathering has created a striking landscape but poor agricultural soil due to the lack of other minerals. Terra Rossa, on the other hand, is noted for both its red coloration and for producing fine grapes. (See References 1, 3, & 4)

References

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