graphite
//ˈɡræf.aɪt//
Noun
1
A soft, dark gray crystalline form of carbon used as a lubricant, in pencils, and as a moderator in nuclear reactors.
Pencil leads are made of graphite mixed with clay.
2
The material forming the core of a pencil that leaves marks when drawn across paper.
The graphite in this pencil is very soft and leaves dark marks on paper.