It is a naturally occurring allotrope of carbon, known as "black lead" or "pencil lead" in its high-purity form. The chemical formula is C and the atomic number is 6. It has a layered structure, in which carbon atoms form a hexagonal planar network structure with sp ² hybridized orbitals, and are stacked on top of each other through weak van der Waals forces. Due to its low hardness, it can leave marks on paper and is therefore used as a lead material for pencils. Graphite has good electrical and thermal conductivity, which makes it widely used in fields such as battery electrodes, electric brushes, and lubricants. Lubrication also makes it an ideal material for manufacturing mechanical parts and seals.