Diamonds are formed deep within the Earth's mantle under high pressure and high temperature conditions. Volcanic pipes, during eruptions, quickly bring these diamonds to the surface, thus transporting them from the depths of the Earth to its crust.
Diamonds do not form on the surface, but are created at great depths, about 150 to 200 kilometers below our feet. At that depth, the pressures are enormous and the temperature rises to around 1300 degrees Celsius: just the extreme conditions needed for carbon to crystallize into diamonds. There, carbon is compressed so tightly that its atoms form incredibly strong bonds, resulting in that famous ultra-resistant and transparent structure. These precious stones remain trapped in the Earth's mantle until violent volcanic activity brings them back to the surface.
Diamonds form deep underground — about 150 to 200 kilometers below the Earth's surface — and normally remain trapped there. But sometimes the Earth offers them a quick express route to the surface through volcanic pipes, known as kimberlite pipes. They act like high-speed natural elevators: the magma, rich in gas and materials from the depths, rises quickly, capturing the diamonds along the way and bringing them intact to the surface. This ascent is ultra-rapid, taking only a few hours or days, thus preventing the diamonds from becoming unstable or transforming into graphite. Without these pipes, diamonds would remain quietly hidden beneath our feet, out of our reach.
When magma rises quickly to the surface, it cools down very rapidly. This rapid cooling is a crucial point, as it allows diamonds to be preserved without transforming into graphite, a much softer and decidedly less elegant form of carbon! If the magma took its time to cool, the diamonds would have plenty of time to revert to a more stable form at the surface, thereby losing all their value. Thanks to this rapid drop in temperature, the crystalline structures of diamonds remain intact and their beauty remains frozen in time.
During their journey to the surface, diamonds remain chemically stable because they are composed solely of pure carbon, formed under immense pressure and high temperatures in the Earth's mantle. In these conditions of rapid ascent, kimberlitic magma primarily acts as an express elevator for diamonds without affecting their chemical structure. In other words, the rapid rise limits the contact time between the diamonds and the magma, protecting these precious crystals from potential dissolution or alteration during the journey. Furthermore, diamond has an incredible chemical resistance, allowing it to maintain its crystalline structure even when passing through very hot or aggressive environments. That is why when they arrive near the surface, these precious gems remain intact, sparkling, and chemically unchanged.
Diamonds rise to the surface through volcanic rocks called kimberlites and sometimes lamproites. These rocks, originating from significant depths, ascend very rapidly during an explosive volcanic eruption, allowing diamonds to be brought back to the surface layers. These rapid ascents limit the possibility of diamonds transforming into graphite during their journey. Once at the surface, these volcanic structures form funnel-like shapes called volcanic pipes, where diamonds are naturally concentrated among other minerals. The density of diamonds causes them to remain trapped in these pipes rather than being widely dispersed around. Additionally, the gradual erosion of the superficial volcanic rocks gradually exposes the buried diamonds to depths accessible for mining.
The largest rough diamond ever discovered, the "Cullinan," came from a volcanic pipe in South Africa; it originally weighed over 3,100 carats, which is approximately 621 grams!
The volcanic rock known as kimberlite, which is the source of diamond-bearing volcanic pipes, is named after the city of Kimberley in South Africa, where it was first discovered.
The ascent speed of kimberlitic magma to the surface is so rapid that it can reach up to 70 km/h, allowing diamonds to maintain their structure without transforming into graphite.
Even though diamonds are made up solely of carbon, it is the very compact crystalline arrangement of the atoms that makes them extremely hard and resistant to abrasion; that is why they are used in the industry to cut or grind various materials.
Synthetic diamonds essentially have the same physical and chemical properties as natural diamonds. The main difference lies in their formation in a laboratory under artificially controlled conditions, as opposed to natural diamonds that form naturally in the Earth's depths and are extracted from volcanic pipes.
Magma in volcanic conduits can originate from more than 150 kilometers deep. At this depth, the temperature and pressure conditions allow for the formation and preservation of diamonds before their rapid ascent to the surface.
Even though diamonds can theoretically burn at high temperatures, their rapid ascent to the surface usually doesn't give them time to react with the surrounding magma. Their chemical structure and the quick ascent protect them from prolonged thermal impacts.
Although volcanic pipes are the main vector, some diamonds can reach the surface through slow tectonic processes, particularly through continental plate movements or subduction. However, these phenomena are still rare and generally not very prolific.
The geological prospecting of these kimberlite pipes utilizes multiple indicators: the presence of typical indicator minerals such as pyrope garnet, chromiferous spinel, or magnesian ilmenite, as well as geophysical techniques like magnetometry, satellite analysis, and finally specific drilling for final validation.
No, only certain volcanoes that originate from the Earth's mantle have the specific conditions to allow for the formation and ascent of diamonds. These are particularly volcanic pipes known as kimberlitic or lamproitic.
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