The mineral commonly known for its use in pencils is graphite. Graphite is a form of carbon that is soft, black, and has a layered structure, allowing it to easily slide and produce marks on paper. It was first used in the 16th century when large deposits were discovered in England. The ability of graphite to leave a mark without producing dust made it ideal for pencil production. Pencils typically contain a mixture of graphite and clay, which determines the hardness or softness of the pencil lead.