The mineral commonly used in pencils is graphite. Graphite is a form of carbon that is soft, black, and has lubricating properties, making it ideal for writing and drawing. In pencil manufacturing, graphite is mixed with clay and other materials to create a core that can be easily sharpened and produces a smooth writing experience. The hardness of the pencil lead is determined by the ratio of graphite to clay, resulting in different grades of pencil, from hard (H) to soft (B). Graphite's unique properties have made it a staple in both educational and artistic settings since its widespread use began in the late 16th century.