The writing core of a standard graphite pencil is made primarily from graphite.
Modern pencil cores usually combine graphite powder with clay and other binders. The mixture is shaped, dried, and fired before being placed inside a wooden or other protective casing. Changing the graphite-to-clay ratio produces harder or softer marks: more graphite generally makes a darker, softer core, while more clay produces a harder, lighter one.
The familiar word “lead” comes from an old misunderstanding. A large graphite deposit discovered in Borrowdale, England, in the sixteenth century was initially thought to be a form of lead. The material was therefore associated with names derived from the Latin word for lead ore, even though pencil cores have not been made of the element lead.
Graphite is also why pencil marks can be erased: loose graphite particles adhere to paper but can be lifted or rubbed away more readily than ink.