The word "diamond" comes from the Greek word adamas meaning "unbreakable" or "hardest substance." Diamonds are the hardest known natural material on earth. In fact, if you happen to own a diamond, you own a piece of history—prehistory, to be exact. Naturally formed diamonds are approximately 3.3 billion years old. Most diamonds are found in rock that was solidified from volcanic magma. It is this volcanic magma that transports diamonds from the Earth's mantle to the surface.
What's the chemical composition of diamonds? Diamonds are nothing more than a bunch of covalently bonded carbon atoms, together for a good time. The electron configuration of carbon is 1s22s22p2, with 4 valence electrons. Diamonds are made up of repeating units of carbon atoms joined to four other carbon atoms though very strong covalent bonds. A rigid tetrahedral network of carbon atoms is formed where all neighboring atoms are the same distance apart.
What about graphite (the stuff we call pencil "lead")? It's made up of a bunch of carbon atoms, too. How come it's not so sparkly? If we compare the structures of diamond and graphite, we see that the carbon atoms are rearranged. That's because the atoms are bonded together in different ways.