3: Weathering, Clay Formation, and Soil Formation
- Page ID
- 33097
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This chapter shows how some Earth materials (minerals and rocks) are broken down (weathered) to form sediment (loose material), clays (tiny material), and soil (loose material formed in place and not transported).
- 3.1: Weathering
- The main processes of mechanical weathering include exfoliation, freeze-thaw, salt crystallization, and the effects of plant growth and results in a reduction in size. Chemical weathering takes place when minerals within rocks are not stable. Some of the important chemical weathering processes are hydrolysis of silicate minerals to form clay minerals, oxidation of iron in silicate and other minerals to form iron oxide minerals, and dissolution of calcite.
- 3.2: Products of Weathering and Erosion
- The products of weathering and erosion are the unconsolidated materials that we find around us on slopes, beneath, beside and on top of glaciers, in stream valleys, on beaches, and in deserts. The other products of erosion: clays and dissolved ions like calcium, iron, and magnesium can be washed out into the oceans to form sediments on the sea floor.
- 3.3: Clay Minerals
- Clay minerals are sheet silicates, made up of tetrahedral and octahedral layers with differing arrangements. They form from the weathering and hydrothermal alteration of other silicate minerals. Clay minerals are soft and weak, and so a mass of clay is typically malleable and can be formed into useful shapes. Clays are almost always fine grained, and they attract ions in solution, and so are important to agriculture and pollution control.
- 3.4: Soil Formation
- Soil is a mixture of fine mineral fragments (including quartz and clay minerals), organic matter, and empty spaces that may be partially filled with water. Soil formation is controlled by climate (especially temperature and humidity), the nature of the parent material, the slope (because soil can’t accumulate on steep slopes), and the amount of time available. Typical soils have layers called horizons.