Diamonds have captivated humanity for centuries, admired for their exceptional beauty, unparalleled hardness, and rarity. Their journey, from formation deep within the Earth to discovery on the surface, is a testament to immense geological forces and vast spans of time.
Deep Earth Formation
Natural diamonds originate far beneath the Earth’s surface, typically at depths ranging from 150 to 200 kilometers (90 to 120 miles) within the upper mantle. This region provides the specific conditions necessary for carbon atoms to crystallize into the dense, stable structure of a diamond.
The environment in which diamonds form is characterized by extreme pressure and high temperatures. Pressures range from 45 to 60 kilobars (approximately 45,000 to 60,000 times atmospheric pressure at sea level). Temperatures in these depths are between 900 and 1,300 degrees Celsius (1,652°F to 2,372°F). These intense conditions coerce carbon atoms into a tightly bonded, three-dimensional crystalline lattice, giving diamonds their inherent hardness.
The carbon source for these diamonds can be primordial carbon, present since Earth’s formation, or recycled carbon from oceanic crust and carbonates subducted deep into the mantle. This transformation process is not instantaneous; natural diamonds take between 1 billion and 3.3 billion years to form, representing a significant portion of Earth’s geological history. The presence of fluid or melt compositions in the mantle, often rich in carbon, facilitates the crystallization process.
Journey to the Surface
After their formation in the deep mantle, diamonds ascend rapidly to the Earth’s surface. This journey is facilitated by deep-seated volcanic eruptions. These explosive eruptions bring diamonds from their stable environment to much shallower depths.
The primary conduits for this transport are volcanic pipes, kimberlite and lamproite. These vertical, carrot-shaped structures extend from the mantle through the Earth’s crust. The magma within these pipes rises quickly, preventing the diamonds from reverting to graphite, which would occur if their ascent were too slow.
The speed of this volcanic transport is important for preserving the diamonds’ crystalline structure. Magma can travel at rates of 20 to 30 miles per hour, bringing diamonds from high pressure and temperature conditions to the surface in a matter of hours. Kimberlite and lamproite magmas do not form diamonds themselves; they serve as the transport mechanism, carrying already-formed diamonds.
Locating Diamond Deposits
Diamonds are found in two main types of geological deposits: primary and secondary. Primary deposits are the kimberlite and lamproite pipes themselves, where diamonds are found in their original host rock. These pipes are the most economically significant source of diamonds, though only a small percentage of discovered pipes contain enough diamonds to be commercially viable.
Identifying primary deposits involves searching for specific indicator minerals found alongside diamonds in kimberlite. These minerals, such as garnets, chromite, and ilmenite, signal the potential presence of a kimberlite pipe. Geophysical surveys, including magnetic and gravity surveys, also help locate these pipes, as kimberlites have unique magnetic and density characteristics.
Secondary deposits, also known as alluvial or placer deposits, form when diamonds are eroded from their primary kimberlite or lamproite sources. Rivers, glaciers, and other natural forces transport these diamonds away. Due to their high density, diamonds accumulate in riverbeds, ancient stream channels, and coastal areas. These deposits often contain higher quality diamonds, as the erosion process naturally removes weaker, flawed stones.
Major Diamond-Producing Regions
Diamond mining occurs globally, with several countries leading in production. Russia is a prominent producer, often holding the top position in terms of carat volume, with much of its output coming from its vast Siberian regions.
Botswana is another leading producer, notable for the high value of its diamonds and the substantial role its mining industry plays in the country’s economy. Canada has emerged as a significant player, with diamond discoveries in its northern territories. Other diamond-producing nations include the Democratic Republic of Congo, Australia, and South Africa, which has a long history of diamond mining, particularly around the Kimberley region.