The mineral known for its use in pencils is graphite. Graphite is a form of carbon characterized by its layers of atomically bonded carbon atoms, which can slip over one another, giving it a slippery consistency. In pencils, graphite is mixed with clay to produce leads of varying hardness, depending on the desired writing style. The "H" scale (for hard leads) and "B" scale (for soft leads) on pencils refer to the ratio of graphite to clay in the mixture. Aside from its use in pencils, graphite is also utilized in lubricants and batteries due to its electrical conductivity.