It is hard to believe that charcoal-like graphite and sparkling diamonds are made of the same carbon, but the reason they are so different is that the way carbon is bound together is completely different.
Diamonds are formed at great depths, as deep as 100 km underground. At such depths, the temperatures are high, the pressures are high, and the forces around them are quite strong. This is the reason why the carbon is bound together so strongly to form diamonds.
It is very rare to find diamonds on the surface of the earth, as they can only be formed 100 km underground. This is why diamonds can only be found in small quantities. Diamonds are very beautiful, but there are only a few of them on the earth. This is why everyone wants them and why they are naturally expensive.