Graphite, like diamond, is an allotrope of carbon. They are very similar to each other but the structure of the atom affects the chemical and physical properties. Graphite is made of layers of carbon atoms. These layers can slide over each other very easily. This means that it is very soft. It is a dull gray in appearance. Due to the delocalized electrons between the layers, it can conduct electricity very well.
Graphite can be formed from coal put under high heat and pressure. Also, graphite can be turned into diamond with enough heat and pressure. This is how synthetic (man-made) diamonds are made.