Diamonds Education

How Diamonds Are Formed

You don’t have to visit a natural history museum to have an up-close and personal encounter with a geological phenomenon. In fact, if you’ve got a diamond engagement ring, diamond earrings, or a diamond bracelet, you may be wearing one right now! To fully understand the natural wonder of diamonds, let’s take a look at how they’re formed.

The word “diamond” originates from the Greek word “adamas”, meaning indestructible and invincible. Diamonds are the only gems composed entirely of carbon. The sixth most common element on earth, carbon is present in all organic molecules. With regard to diamond formation, it’s the particular arrangement of the carbon atoms that makes each stone truly unique.

Diamonds are the crystalline form of elemental carbon, with carbon atoms arranged in an isometric-hexocrahedral crystal lattice that is remarkably hard and disperses light well. In order for diamonds to form, carbon must undergo very specific conditions. The air pressure must range between 45 and 60 kilobars (60,000 times normal air pressure at sea level) and the temperature must be between 1652 and 2372 F (900-1300 C).

Diamonds are formed deep within the earth’s lithospheric mantle, located 75-120 miles beneath the earth’s surface. At these great depths, the carbon atoms in the earth’s mantle and in fossilized microorganisms are subjected to intense pressure and temperature changes. When carbon-rich rock submerges in the earth’s mantle, carbon atoms become liquefied. When the temperature dips and specific pressure and temperature conditions are met, the carbon atoms then crystallize and form diamond-bearing rock.

Once the loose diamond has formed and hardened, it can take thousands of years for geologic events to bring the crystals to the surface where they can be mined. One way diamonds are brought to the surface is via volcanic pipes, which are carrot-shaped magma channels of deep-origin volcanoes. In volcanic pipes, magma has carried deep-formed rocks and minerals to the surface where they can be mined as a primary source of diamonds. Secondary sources of diamonds include areas where water or wind has eroded the surface of volcanic pipes, such as alluvial deposits that are found along riverbeds and shorelines.

The diamond ore mining process is labor intensive, and yields a very small fraction of actual diamonds. Only 25% of the mined diamonds are considered of a high enough quality to be used in fine jewelry, with the remainder being used as abrasives or for the industrial use of diamond cutting, drilling, grinding, and polishing equipment. Today, most gem-quality diamonds are mined in Brazil, Russia, South Africa, Canada, and Australia.

Understanding how diamonds are formed results in a greater appreciation of this geological marvel. From the time carbon atoms are liquefied in the earth’s lithospheric mantle until they reach your finger or earlobe can span an astonishing 45 million years. The diamond’s longevity, brilliance, and complexity combine to make it the consummate symbol of eternal love and loyalty.