Diamonds form between 75-120 miles below the earth's surface. According to geologists the first delivery of diamonds was somewhere around 2.5 billion years ago and the most recent was 45 million years ago. The carbon that makes diamonds comes from the melting of pre-existing rocks in the Earth's upper mantle. There is an abundance of carbon atoms in the mantle. Temperature changes in the upper mantle forces the carbon atoms to go deeper where it melts and finally becomes new rock, when the temperature reduces. If other conditions like pressure and chemistry is right then the carbon atoms in the melting crystal rock bond to build diamond crystals.
There is no guarantee that these carbon atoms will turn into diamonds. If the temperature rises or the pressure drops then the diamond crystals may melt partially or totally dissolve. Even if they do form, it takes thousand of years for those diamonds to come anywhere near the surface.
It takes millions of years to make a diamond. When you own a diamond, you own something which is a legend in the making. It has not been made in a factory just the other day. A diamond comes from the bosom of the earth. More interestingly not all the diamonds mined are made into jewelry. Only one fourth of the diamonds that are mined are made into jewelry. Every 100 tons of mud produces one carat of a diamond. And this one carat is not one stone! It could be anything from 0.005 ct to 1 ct. because much of the original stone is cut away in the process of cutting, shaping and polishing the diamond.
Diamonds come in different rough shapes. The next time you look at your diamond, think about the amount of time, energy and resources have gone into making that one.