Clay

Origins of Clay

Weathering and Erosion of Rocks

Clay is formed from the erosion of a limited variety of environments. Some of these environments include:

1. Continental, which is the weathering and erosion on Earth's surface

2. Marine, which occurs on the floor of a body of water or within the Earth when it is near a heat source.

On the surface of the Earth, erosion by rain, wind, or animals leads to the continuous breakdown of particles. Most often, clays are formed due to chemical weathering, by low concentration carbonic acids or other solvents. These solvents leach through parent rock material and chemically break them down. Eventually, enough weathering occurs to form clays, which are less than .002mm in diameter. Some clays may form due to hydrothermal activity, where hot water circulates material over enough time to break them down to fine-grained particles.

Properties of Clay

Clay Size Relative to silt and Sand

Clays can be found in a multitude of colors based on the minerals present, including red, brown, and even white. Clays deform plastically due to their structure and water content, meaning the physical changes are permanent. They become non-plastic when exposed to high heat or are dehydrated. Depending on the discipline, clays are classified based on their particle size, water content, or plasticity, which can distinguish them from similar particles such as silt. Atterberg limits can be tested which are a measure of the shrinkage limit, plastic limit, and liquid limit.

In order to be classified as clay, the particles must meet certain criteria. The grain size must be less than .002mm, resulting in a very high surface area. Clays have the ability to bond with water from the soil due to their molecular structures. Clays are made up of various minerals which are classified as hydrous aluminum phyllosilicates. These minerals may be iron, alkali metals, alkaline earth, or other cations that may be found in the surrounding soil. The basic structure of the phyllosilicates is based on interconnected six-member rings of SiO4-4 tetrahedra that extend outward in infinite sheets. Phyllosilicates may contain additional molecules such as hydroxyl ions and cations. This results in two basic groups of sheet silicates:

1. The trioctahedral sheet silicates where each O or OH ion is surrounded by 3 divalent cations, like Mg+2 or Fe+2.

2. The dioctahedral sheet silicates where each O or OH ion is surrounded by 2 trivalent cations, usually Al+3.

These molecular structures build upon themselves, resulting in sheet minerals such as talcs and micas. These minerals can be found in parent rocks and serve as the structural basis of clays, which allow them the ability to bond with water. However, in addition to these essential minerals which allow water to bond, clays can be made up of metal oxides, quartz, and organic material. These characteristics are essential to plant and animal life in soils, and these porous spaces between clay grains facilitate the creation of microhabitats and communities that contribute to the complexity and heterogeneity of soil.

Residual Clay

Residual clay is what is left behind after the erosion processes of the parent rock material. This type of clay is most often formed from weathering on the earth's surface, which can happen in a few different ways. One way is chemical weathering through solvents. Another example is when rocks such as limestone containing insoluble impurities are weathered and left behind as clay deposits. Once this happens residual clay is formed and can then be harvested for different uses. Residual clay is considered to have low plasticity and will not stick together very easily, limiting its uses.

Sedimentary Clay

Sedimentary clay consists of minerals broken down from the original parent material through weathering and erosion. They are then transported by wind, water, ice, or any other mode of transport away from the parent rock. As these particles are being transported they are suspended in the water because they are so small. They will only be deposited when the clay particles bump into each other causing them to stick together and sink down to the bottom of the river. Due to the water-clay bonds, clays can often act as larger particles such as silt of sand and require higher forces to be moved or changed. When they get moved there are eroded further causing them to decrease in their size. This type of clay is considered to have more plasticity this means it will form a stickier soil.

Organisms That Live in Clay

Clay is not very suitable for many plants to live in, as air has a hard time getting through the soil to the roots because the soil is packed so tightly. There is also a drainage problem with clay dominant soils. Some plants that can tolerate these conditions are coniferous trees such as pine trees, spruce, balsam fir, and tamarack trees. Some deciduous trees also can grow in clay dominant soils like willows, crabapple trees, and some maples. There are also some organisms that live within the predominantly clay soil as well. Macro-fauna like earthworms and insects, and microfauna like bacteria, nematodes, and other microscopic organisms can live within clay soil. To increase the ability for animals and plants to thrive in clay-dominated soils, peat moss can be tilled in. Peat moss will increase the carbon content in the soil, thus allowing them to absorb more nutrients and thrive.

• 

  MacroFauna

• 

  Mesofauna

• 

  Microfauna

---

References

• [1] "Clay Types, Geology, Properties and Color Chart (GcCeramics) - Meeneecat." Google Sites. N.p., n.d. Web. 14 Apr. 2018.

• [2] "Earth Sciences: London's Geology." Clays and Clay Minerals. N.p., n.d. Web. 14 Apr. 2018.

• [3] "How Is Clay Formed? Is It Inorganic or Organic?" The Clay Ground Collective. N.p., n.d. Web. 14 Apr. 2018.

• [4] "Trees and Shrubs for Clay Soil." Trees and Shrubs for Clay Soil : UMN Extension. N.p., n.d. Web. 14 Apr. 2018.

• [5] Environmental Characteristics of Clays and Clay Mineral Deposits. N.p., n.d. Web. 14 Apr. 2018.

• [6] Kodama, Hideomi, and Ralph E. Grim. "Clay Mineral." Encyclopædia Britannica. Encyclopædia Britannica, Inc., 20 Feb. 2014. Web. 14 Apr. 2018.