graphite - Wiktionary
An allotrope of carbon, consisting of planes of carbon atoms arranged in hexagonal arrays with the planes stacked loosely, that is used as a dry lubricant, in "lead" pencils, and as a moderator in some nuclear reactors. 1928, Lawrence R. Bourne, chapter 4, in Well Tackled![1]: Technical terms like ferrite, perlite, graphite, and hardenite were ...