The mineral often used in pencil lead is graphite. Graphite is a form of carbon that is layered in structure, allowing it to be used effectively for writing and drawing. Its unique properties include a slippery feel, high conductivity of electricity, and resistance to heat, making it ideal for various applications beyond pencils, such as lubricants and batteries. The "lead" in pencils is actually a mixture of graphite and clay, which can be adjusted to produce different degrees of hardness. The popularity and ease of use of graphite have made it a staple in writing instruments worldwide.