Hobbies And Interests
Pressure
General Patton was quoted as saying, "pressure makes diamonds." Though the diamonds he was referring to were military and metaphorical, it's very much the truth for mineral diamonds. Most natural diamonds form at tremendous depths beneath the Earth's crust, from 150 to 200km (93 to 124 miles) down where the pressure is tens of thousands of times greater than atmospheric pressure. The diamonds we find at the earth's surface and in mines have been transported upwards from where they were formed by tectonic action and ancient lava floes.
Heat
Although tremendous pressure is required in order to create diamonds from elemental carbon, heat is required as well. Diamonds are typically forged at the fiery temperatures of 900 to 1,300 Celsius (1,650 to 2,350 Fahrenheit). There is a relationship between the temperature and pressure required for a diamond to form, where greater temperature requires greater pressure. Synthetic diamonds are typically formed at higher temperatures and pressures (upwards of 2,000 Celsius) because of the third consideration: time.
Time
Not only does it take extreme temperature and pressure to create a diamond, but it also takes time. It takes time on the order of hundreds of millions to billions of years for diamonds to form naturally. Synthetic diamonds would be impractical if the process took this long, but formation occurs faster at the significantly higher temperatures and pressures used in those processes.
Access
While this is not a process strictly required for the formation of natural diamonds, it is important to have access to them. The areas in which diamonds are forged are essentially inaccessible to humans or machinery. There are natural processes that bring diamonds to the surface along with many other rocks and minerals. Tectonic plates move against one another, bringing material to the surface with their shifting and also allowing magma to carry molten minerals (including diamonds) much nearer the surface.