answered question
Pencils contain graphite & clay, plus some wax (the wax is added for lubrication).  The responses provided above are correct, but the information in the chart reproduced below might be of interest to you. [The chart is from :
Sousa MC, Buchanan JW. "Observational models of graphite pencils". Computer Graphics Forum 19.1 (2000): 27-49. P. 30. … Read more
answered
Pencils contain graphite & clay, plus some wax (the wax is added for lubrication).  The chart reproduced below is from :
Sousa MC, Buchanan JW. "Observational models of graphite pencils". Computer Graphics Forum 19.1 (2000): 27-49. P. 30. Bear in mind that value will vary somewhat between manufacturers (NB - Sousa & Buchanan neglect to … Read more