Illite is a type of clay mineral that is commonly found in sedimentary rocks. It is part of the mica group and is characterized by its fine-grained structure and ability to retain water. Illite forms from the weathering of other minerals and is often associated with shale and mudstone. This mineral is important in various fields, including geology and agriculture. In geology, illite helps scientists understand the history of sedimentary environments. In agriculture, it improves soil structure and water retention, making it beneficial for plant growth.