Illite is a type of clay mineral that is commonly found in sedimentary rocks. It is characterized by its fine particle size and is often formed from the weathering of other minerals, such as feldspar. Illite is known for its ability to retain water and nutrients, making it important for soil health and agriculture. This mineral is typically non-expanding, meaning it does not swell significantly when wet, unlike some other clay minerals like montmorillonite. Illite is often used in various industrial applications, including ceramics and drilling muds, due to its unique properties and stability.