Diamonds are the hardest natural substance, formed from pure carbon deep within the earth’s crust. They form at a depth of 90 miles and are brought to the surface by rare volcanic eruptions. Kimberlite is an indicator of their presence, but they can also be carried by glacial action. The majority of diamonds are mined in southern and central Africa, with De Beers Group owning and operating many of the mines. Diamonds are cut and polished in various locations worldwide, including New York, Antwerp, and Tel Aviv.
Diamonds are the hardest naturally formed material on Earth, renowned for their beauty, strength and durability. They have been known and accumulated by humans for thousands of years and their name comes from the Greek word for invincible.
These stones come from deep within the earth’s crust, formed there by incredible pressure and relatively manageable temperatures. They form under the continental crust, from pure carbon. This carbon can come from purely non-organic sources, organic sources, or a mixture of the two. Diamonds formed from inorganic carbon are called harzburgitic diamonds, while those formed from a certain amount of organic carbon are called eclogitic diamonds.
Diamonds form at a depth of about 90 miles (150km), over millions and millions of years. The temperature at which they form is in the range of 2,000° Fahrenheit (1,100° Celsius) – too much hotter than this and conditions are no longer suitable for their formation. Most are over a billion years old by the time they reach the Earth’s surface, with some diamonds more than three billion years old, not much younger than the Earth itself.
Stones come to the surface when magma from far below the earth’s surface begins to rise. Since they are found at such incredible depths—three to four times deeper than the depth at which a normal volcano originates—eruptions of magma deep enough to bring them to the surface are relatively rare. Once this magma cools, it forms a rock known as kimberlite – or sometimes lamproite – which can be used as an indicator of the presence of diamonds in that area.
By mining in one of these kimberlite dams, or kimberlite pipes, diamonds can be discovered. Of course, the presence of kimberlite does not necessarily guarantee that the gemstones will be present, merely that the volcanic surge originated deep enough for the diamonds to form. Often these kimberlite dikes will erode over time and the gemstones will be carried away with the sediment, to build up in basins somewhere.
While kimberlite dams are the most common place diamonds can be found, others exist as well. In some cases, glacial action can pick up diamonds and carry them many hundreds of miles, leaving them behind in their tracks or when they eventually melt away. This has led to the discovery of stones in geologically inappropriate locations, but not in sufficient quantities to make tracking glacial trails a viable hunting method.
Extremely small diamonds can also be formed under certain extraordinary conditions. Such micro diamonds are sometimes formed, for example, when meteors hit the earth’s surface. While not large enough to be particularly valuable, they serve as a reliable indicator of meteor impact craters.
For many centuries India was the world’s leading source of diamonds, but eventually these sources were mostly depleted. In the modern world, nearly half of all that is mined comes from mines in southern and central Africa. Most of these mines are owned and operated by various companies in the De Beers Group, which is responsible for more than 40% of diamonds by value worldwide and has held a virtual hold on the world market since its formation in 1860 Large-scale mines also exist in Brazil, Australia, Siberia and parts of Canada. Once mined, these diamonds travel the world to be cut and polished to create the beautiful gemstones we all know. Most of the cuts take place in some areas of the world, especially New York, Antwerp and Tel Aviv.
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