The diamond is a fascinating form of pure carbon where atoms are locked into an extremely rigid crystal lattice structure. This unique atomic arrangement grants the mineral its legendary hardness and brilliance, contrasting sharply with graphite, which is made of the same element but has a much softer, layered structure. The question of how many diamonds exist on Earth yields two vastly different answers depending on whether one considers the planet’s inaccessible interior or the commercially available supply. The scarcity often associated with diamonds applies only to the tiny fraction that has been naturally delivered to the surface, where it can be discovered and mined. The great majority of the planet’s diamond inventory remains locked away in the deep Earth, representing an astronomical geological total.
The Geological Origin of Diamonds
Diamond formation requires a very specific and extreme set of physical conditions that exist only deep within the Earth’s mantle. Carbon atoms must be subjected to temperatures ranging from 900 to 1,300 degrees Celsius. Simultaneously, the pressure must be immense, typically falling between 45 and 60 kilobars, which is equivalent to 4 to 6 GigaPascals.
These conditions are met at depths of approximately 150 to 250 kilometers beneath the surface. This stability zone is most commonly found beneath ancient, stable continental interiors known as cratons. Cratons are characterized by thick lithospheric roots, which act like deep keels that extend far down into the mantle, providing a long-term, stable environment for diamond preservation.
Most natural diamonds are billions of years old, having formed and resided in this stable environment for extended periods. Carbon-bearing fluids or melts within the mantle precipitate the carbon atoms into the dense, cubic crystal structure we recognize as diamond. Without the sustained high pressure of the cratonic roots, the diamond structure would ultimately break down into the more stable form of carbon, graphite.
Estimating the Deep Earth Reserve
The vast majority of the Earth’s diamonds are not only unminable but were, until recently, only theoretically estimated. Scientists have leveraged global seismic data to create a more accurate estimate of this deep reserve. The method relies on analyzing the speed at which seismic waves travel through the Earth’s interior after earthquakes.
Researchers discovered that seismic waves move unusually fast through the deep roots of continental cratons. Standard rock compositions could not account for this observed high velocity, but diamond, being extremely stiff, transmits sound waves significantly faster than most other minerals. Modeling revealed that the fastest travel times could be explained if the cratonic roots contained a diamond content of between one and two percent by volume.
When this small percentage is multiplied by the enormous volume of all cratonic roots worldwide, the total mass is staggeringly large. Scientific studies estimate that there may be a quadrillion tons of diamond scattered within these deep mantle reservoirs. This colossal reserve sits at depths of 145 to 240 kilometers (90 to 150 miles) below the surface, far exceeding the reach of any current mining technology. The immense total serves as a reminder that the rarity of diamonds is purely a function of geological accessibility rather than planetary abundance.
Mechanisms for Bringing Diamonds to the Surface
For diamonds to become accessible, they require a rare, high-speed geological transport system from the mantle to the crust. This is achieved through a specific type of volcanic eruption that bypasses the slow, destructive processes of normal plate tectonics. The primary mechanism involves deep-source magmas that originate below the diamond stability field and rapidly ascend through the lithosphere.
These violent eruptions create narrow, carrot-shaped geological structures known as kimberlite pipes. The kimberlite magma, rich in volatile components like carbon dioxide and water, is forced upward, acting as a geological elevator for the diamonds. The ascent must be extremely rapid, measured in hours or days, to prevent the diamonds from being converted back into graphite as the pressure decreases nearer the surface.
The resulting kimberlite rock, which is the host for most mined diamonds, is formed when this deep magma cools within the pipe structure. A secondary, though less common, host rock is lamproite, which forms similar pipe structures. The diamonds themselves are accidental passengers, fragments of the deep mantle carried along by the explosive force of the eruption.
Global Accessible Reserves and Annual Supply
Contrasting sharply with the quadrillion tons of deep-earth diamonds is the measurable and economically viable reserve available for mining. This reserve is defined by diamonds concentrated enough in kimberlite and lamproite pipes to warrant the massive expense of extraction. Global estimates for these recoverable reserves currently stand at approximately 1.8 billion carats.
The annual global production of rough diamonds currently hovers around 90 to 105 million carats. This production comes primarily from a handful of major mining regions, with Russia and African nations like Botswana and Angola holding the largest known reserves.
At the current rate of extraction, the world’s known economically viable diamond reserves are estimated to sustain the market for about 20 years. This relatively short lifespan of major mines underscores the finite nature of the accessible supply. The depletion of these primary pipe deposits means that the accessible number of diamonds is a non-renewable resource that is steadily shrinking.