Science & TechFact
Diamond and pencil lead are made of exactly the same stuff.
Both are pure carbon. In diamond, every atom bonds tightly to four neighbours in a three-dimensional lattice, hence the hardness. In graphite, hexagonal sheets stack on top of each other and slide easily, which is why a pencil writes. Under normal conditions graphite is actually the more stable form; diamond converts only immeasurably slowly.
Useful: Lab-grown diamonds are now made in weeks from methane in a plasma reactor and are chemically identical to natural ones.
Source: en.wikipedia.org