How Are Diamonds Made?
Millions of years ago the ancient oceans had microorganisms that lived and died in the oceans. When the microorganisms died there bodies fell to the ocean floor. After the bodies decomposed, what was left was almost pure carbon. The crust of the earth surface is in constant motion. Movement is due to tectonic plates and the continental drift. Read more on the History of Carbon.
When one of the tectonic plates was pushed under another the bodies of the microorganism, now carbon, is also buried under tons of rock. The carbon is subject to extreme pressures by the rock pressing down upon it and by extreme heat, which is usually between 1100, and 1400 degrees Celsius. If the carbon being acted upon is pure then the diamond will be colorless which is normal for diamonds. If nitrogen or sulphur is also included in the carbon then some color may be added to the diamond.
This process preserves the unique crystal structure that makes diamonds the hardest natural material known. The arrangement of the atoms causes the diamonds to have tighter atoms than any other substance in the world. When volcanoes erupted, every once in a while, the microorganisms, which are now diamonds, are forced to the service. Conventional diamonds are mined from explosive volcanic rocks (kimberlites) that transport them from depths in excess of 100 kilometers by volcanic action.
Put pure carbon under enough heat and pressure, about 2,200 degrees Fahrenheit and 50,000 atmospheres and it will crystallize into the hardest material known. That is a very simplistic view and also very hard for man to duplicate.
Modern (man made - synthetic) methods use a very complicated process that requires the crystals to be grown using a special high growth-rate chemical vapor deposition. Then the crystals were exposed to very high pressure and temperatures to make them harder. There is then a production of a chemical reaction that yields what is called carbon rain. The carbon rain atoms arrange themselves in the same structure as the container or seed used to catch the carbon rain. As they arrange themselves into a tight composition, they turn into man-made synthetic diamonds.
Most of the man made or synthetic diamonds are yellow in color because the natural fancy color diamonds are so rare and expensive. Man-made diamonds are very difficult to distinguish from natural ones. A trained jeweler could tell the difference if he could detect the different growth patterns and the lack of inclusions. Inclusions are the tiny bits of material that are usually imbedded in a natural diamond and are considered a flaw. Synthetic diamonds have no flaws. If you are in doubt for the actual value of your diamond, you should have it appraised or have it unmounted and send it into GIA for inspection and certification.