Types of Soil Colloids

Phyllosilicate Clay Minerals

• Phyllosilicate clay minerals are derived from silica, and generally contain aluminum, magnesium and hydroxide. The presence of phyllosilicate clay minerals in soil is responsible for the cracks that form when soils dry out, as the phyllosilicate clay minerals shrink without water, creating the wide, loosely tetrahedral cracks. Clay minerals also help hold nutrients in the soil and help protect soils from weathering.

Oxides

• Soil colloids that are oxides are typically hydrous oxides, or simple oxides of aluminum and iron. Iron and aluminum oxides are found widely in most soils, especially in the forms of gibbsite, hematite and goethite. Oxides, like other types of colloids, are an important feature in holding nutrients in the soil in a process known as cation. Without this process, nutrients would leach down into soils and plants would not be able to access them and, thus, would not be able to grow properly.

Amorphous Minerals

• Many amorphous soil colloids, such as allophone and imogolite, are formed from deposits of volcanic ash. Amorphous minerals do not have a regularly arranged atomic structure like oxides and clay minerals, and are very receptive and fertile minerals in soil.

Organic Colloids

• Organic colloids are mostly referred to as humus, and are made from decomposed and chemically altered organic material. Humus is at a stage where its chemical composition will remain unaltered if the surrounding conditions remain the same, and as such is the final stage of organic decomposition. High humus content gives increased water retention and nutrient retention to soils.