Question

The following picture represents the structure of an important component of clays that is commonly found in many soils. Explain what this picture represents? What are the main elements that may be found in the clay mineral represented in the structure. You may label the diagram, but make sure you hand in this page. What do the spheres shown above and below the lattice in the structure above represent? Give examples of the chemical species that would typically be found in soils, as represented by the spheres shown above and below the lattice. Why are these species found in association with the lattice. Explain your answer. Certain clay minerals are believed to play an important role in the protection of soil organic matter. Explain how this might occur.

Answer 1

a) The structure represents a Montmorillonitey clay mineral structure which is made up of three-layer package, one layer of Al octahedron sandwiched between two layers of SiO₄ tetrahedra

b) Clay as a mineral is a hydrous aluminium phyllosilicate. That means it has the elements Si, O, Al, and H. But they are never “pure”. There is really no such thing as “pure clay”. All clays are mixed results of weathering of rocks. So there is usually also different amounts of a few of these: Fe, K, P, Ca, Na, Mg ,Li, and others.

c) The spehers above and below the given clay structure is exchangeable ions such as Na+,K+,etc . Kaolinite is typically found in soils.Soil is formed by the weathering in a warm moist climate.The Kaolinite mineral is formed when alumina is abundant and silica is scarce, because it requires availability of alumina.

d) Soil organic matter tends to increase as the clay content increases. This increase depends on two mechanisms. First, bonds between the surface of clay particles and organic matter retard the decomposition process. Second, soils with higher clay content increase the potential for aggregate formation. Macroaggregates physically protect organic matter molecules from further mineralization caused by microbial attack.