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Relations Between Iron Oxides, Soil Color, and Soil Formation
Addtime: 2017/01/04 Read:4896 Font size: Large Small
Iron oxides are useful field indicators of pedogenic environments for three reasons: (i) they include several minerals, (ii) these minerals have different colors, and (iii) the type of mineral formed is influenced by the environment.
Therefore, recognizing the Fe-oxide mineral in the field by its color has a potential to yield information about pedogenesis. Hematite-containing soils (usually with associated goethite) have mostly hues between 5YR and 10R, whereas goethite-containing soils with no hematite have hues between 7.5YR and 2.5Y. Orange colors with a hue of 7.5YR and a value of ≥6 are often due to lepidocrocite. Ferrihydrite can be distinguished from goethite by its more reddish hue (5-7.5YR) and from lepidocrocite by its lower value (≤6).
These mineral-specific colors, however, also vary somewhat with concentration, crystal size, degree of cementation, and possibly isomorphous substitution. Poorly crystalline goethite, lepidocrocite, and ferrihydrite may have lower values than better crystalline specimens, and cementation also leads to lower values. Small hematite crystals are bright red (2.5YR-10R), whereas the color of larger crystals or crystal aggregates may reach into the red purple (RP) range.
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