Soil Color and Redox Chemistry

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Sediments in Lake Red Rock, Iowa

ERN Item Type: 

  • Classroom Activities

Organization: 

Soil Science Society of America (SSSA), Earth Science Week (ESW), American Geosciences Institute (AGI)

Description: 

Are soils like M&Ms™? Yes! Typical soil colors are red, brown, yellow, or black. These colors are often not the color of the minerals in the soil but coatings of iron oxides (Fe203, FeOOH, and so on) or organic matter on particles. The minerals beneath are often quartz or feldspar, which are grey. Soil scientists can identify where the water table is even when the soil is not saturated. Consider the M&Ms™ again. What is the chance that the now-white ones will turn red again? Slim to none. Soil is the same. Once the red (rusty) colors due to iron oxides have been removed and the soil is gray, it is unlikely that the particles will become coated (turn red) again. In this activity, students record canned/jarred soil mixtures for color changes and bubbles.

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Earth Science Big Ideas: 

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