Every diamond is unique, but all natural diamonds have at least one thing in common: the beautiful gemstones we admire, wear, and give as gifts today are billions of years old. Here is the story of how diamonds are formed.
Natural diamonds are formed in the heart of the earth, at incredible depths as deep as 500 miles from the surface. On average, diamond formation takes place at depths between 90 and 120 miles. This far into the mantle, the pressure and heat are tremendous. Temperatures in diamond formation zones range between 1652 and 2372 degrees Fahrenheit.
Diamonds make their way to the earth’s surface via volcanic activity, but not just any eruption will do. Most mineable diamonds are borne to the surface via diamondiferous kimberlite, which can be found in cratons (stable portions of a continent) that contain ancient stones from the Archean period. New diamonds that form inside the earth’s mantle remain there until magma eventually pushes them to the surface, either in kimberlite, or in lamprophyre or lamproite rocks. Kimberlite eruptions are rare. In fact, the last one is believed to have occurred over 25 million years ago.
These days, a trip of 90 to 120 miles doesn’t take long to complete; at most, we complete journeys like these over the span of a few hours. Even a longer 500-mile trip can take just a few hours to complete by air. When you’re a diamond, it takes just a little longer to cover that distance. While no one has witnessed a kimberlite eruption, geologists have determined that the process is fairly rapid, with magma moving at a velocity between 4 and 20 meters per second, or a maximum of about 44 miles per hour.
Speed is imperative, as magma that moves too slowly can melt diamonds back into carbon. Once cooled, kimberlite and other host rocks typically remain in craters. Sometimes the force of eruption throws diamondiferous rock long distances, explaining why some diamonds are found outside kimberlite pipes and other cratons. Prior to the 20th century, most diamonds were found in surface or alluvial deposits, usually by a stroke of luck. Famous examples include the Koh-i-noor diamond, the Cullinan diamond, and Hope diamond.
These days, a trip of 90 to 120 miles doesn’t take long to complete… When you’re a diamond, it takes just a little longer to cover that distance.
There’s much more to learn. Geologists frequently uncover new facts about diamonds and how they’re formed, making it easier for mining companies to reach deposits, and paving the way for new processes for creating synthetic diamonds. Some of these factors affect value and diamond pricing, which involves not only miners and other workers, but wholesalers, manufacturers, retailers, and of course, buyers.
Unlike diamond simulants or imitations such as cubic zirconia, synthetic diamonds share physical and chemical properties with natural diamonds. But lab-grown diamonds are formed over a short time ranging from several weeks to a few months. Formation takes place in chambers with either high-pressure, high-temperature (HPHT), chemical vapor deposition (CVD), or low-pressure, high-temperature (LTHP) environments. All three methods rely on diamond crystals or plates, which serve as seeds for growth initiation.
Wherever our diamonds were formed, and however they made their way into our hands, these stones have an amazing story to tell. That story continues as diamonds are bought and sold, given as gifts, passed on as heirlooms, and cherished by those who own them through the ages.
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