The mineral known for its use in pencils is graphite. Graphite is a form of carbon that is soft, opaque, and has a layered structure, making it an ideal material for pencil leads. Its properties allow for smooth writing and the ability to produce darker marks, depending on the pencil's hardness. The strength and stability of graphite enable it to be used in various applications beyond writing, including lubricants, batteries, and even as an electrical conductor. Its unique characteristics make graphite a versatile and indispensable mineral in both everyday items and advanced technologies.