Diamonds are formed by temperatures reaching 2,200 degrees Fahrenheit and pressure up to 725,000 pounds per square inch acting on a carbon-bearing ore within the Earth’s upper mantle over billions of years.
Over 100 miles below the surface of the Earth, diamonds are formed in diamond stability zones. These zones are in the upper mantle of the Earth and the special conditions of high temperatures and pressure are crucial in diamond formation. These conditions are not found across the globe. Instead, they’re thought to occur in the mantle found beneath continental plates’ stable interiors.
How Does the Temperature-Pressure Environment Work?
The high temperatures and pressures needed to form diamonds act on the carbon-bearing ore and arrange the carbon atoms into a diamond lattice, which is a crystal structure. With each compression of carbon atoms, the structure grows until it eventually forms a diamond stone. Another key ingredient in this process is time. A lot of it. The majority of diamonds that have been discovered so far actually began forming between one and a few billion years ago.
Diamonds Found Near the Earth’s Surface
Diamonds are formed so far beneath the Earth’s surface that it’s impossible to drill for them, yet they’re readily found in some deposits near the Earth’s surface.
Deep below the Earth’s surface, pressure is released by the occurrence of powerful volcanic eruptions, carrying molten ore to the surface. The eruptions cause magma to travel quickly through the mantle via Kimberlite pipes, which are cracks in the Earth. When these pipes run through diamond stability zones, the magma undoubtedly passes through, tearing rock away and transporting it to the surface. These chunks of rock are known as xenoliths.
It’s within xenoliths that rough diamonds are usually found. They tend to be embedded in magma as it cools after an eruption. It’s these xenoliths that diamond miners look for, using numerous techniques to extract the diamonds from within them.
Mining for Diamonds
Commercial diamond deposits are those in areas where xenoliths are known to exist from Kimberlite pipes as well as places where Kimberlite areas have been worn down by natural erosion from glaciers, streams or rivers and the diamond deposits have been flushed out. These are called alluvial deposits.
There are three main types of mining used to achieve the highest yields of xenoliths. These are seabed mining, underground mining and open pit mining.
When the xenoliths have been mined, the diamonds have to be pulled from them. The rocks are crushed and milled before the procedure of Dense Medium Separation takes place. Once the ore most likely to have diamonds within it has been separated, a grease belt is used to pull the rough diamonds out.
From Rough Diamonds to Sparkling Gems
The majority of diamonds mined aren’t actually considered to be of gem quality so are separated and used for industrial purposes. Those that are of high quality and a high grade are cut and shaped, transforming the dull surface into a beautiful, sparkling one that’s recognizable as the precious gem used for coveted jewelry.