What are clay minerals?

Clay minerals are hydrous aluminium phyllosilicates that may contain varying amounts of iron, magnesium and alkali metals. These minerals are commonly found in the Earth's near-surface environments and form in soil and sedimentary deposits due to diagenetic and hydrothermal alteration of rocks.

Clay minerals form in the presence of moisture and have been used since ancient times for agriculture and manufacturing. Clay is made up of sheets of interconnected silicates that combine with a second sheet-like grouping of oxygen, hydroxyl and metallic atoms to form two-layer minerals. Clay is a soft earthy material that contains particles that have a size of less than 4 micrometers.