Ah. Now we're getting to the good bit. You've read the pages on diamonds and graphite, and seen their properties and how different they are. Why? They're both made of carbon, aren't they? Yes, they're both pure carbon, but the difference lies in their crystal structure.

The crystal structure of diamond is very rigid. Each atom is joined by a strong covalent bond to four others in a tetrahedral shape. This makes a very strong, rigid mineral. Diamond has a high melting point because it needs more energy to "break" the bonds. It can't conduct electricity because its electrons are not free to move, but it conducts heat because its covalent bonds allow it to spread the heat around easily.

Graphite's atoms are bonded together in layers of hexagons. Each atom is strongly bonded to three others, while the other electron can move around a bit more. The forces of attraction between the atoms in each layer are strong, but the bonds between the layers are weak. The layers can easily slide over each other. This is why graphite is so soft. Graphite is a conductor because the fourth electron can move around.