Diamond (Industrial)

Diamond used not as a gem but as a cutting edge — most of it grown in a press rather than dug out of the ground.

Pourquoi est-ce important ?

Synthetic industrial diamond long ago overtook natural stones. It is also becoming a semiconductor for extreme power electronics.

Where it is in the Earth

Diamond is a form of carbon that crystallises under extreme pressure and temperature — conditions found naturally only deep in the Earth's mantle, at depths broadly exceeding one hundred and fifty kilometres. The carbon atoms arrange themselves into a three-dimensional lattice that is the hardest known natural substance, which is exactly why industry wants it. The pressure required to form diamond cannot be replicated near the surface; the crystals that exist in mineable deposits were created billions of years ago in ancient, stable portions of the continental crust known as cratons, where the mantle beneath is both thick and cold enough to sustain the right conditions.

The mechanism that brings diamond to the surface is a rare and violent one. A type of magma called kimberlite forms deep in the mantle and rises extremely rapidly through cylindrical conduits. Because the ascent is fast — geologically speaking — the diamonds it carries do not have time to revert to graphite, the stable form of carbon at surface pressures. When the eruption reaches the surface and the pressure drops, the magma solidifies into a carrot-shaped body of rock called a kimberlite pipe. A related rock type, lamproite, hosts some deposits by the same general process. These pipes are the primary source of natural mined diamond. Over geological time, erosion can liberate diamonds from a pipe and deposit them in river gravels or coastal sediments, forming what are called alluvial or marine placer deposits, which are also mined.

The geography of diamond deposits follows the geography of ancient cratons. Russia's Siberian craton, the Kaapvaal craton of southern Africa, and the Congo craton together account for the overwhelming majority of known reserves, which is why Russia, Botswana, Congo, Angola, and South Africa dominate the production and reserve tables shown above. The United States has no reported reserves in the dataset. Kimberlite pipes are numerous but most are too small, too deep, or too low in diamond content to be worth mining; only a small fraction of known pipes ever become operating mines.

Getting it out

The method used to extract diamonds from a kimberlite pipe depends largely on how deeply the ore body extends below the surface and how much of the upper portion has already been removed. Early in a mine's life, the top of the pipe is accessible from the open air and the ore is taken by open-pit methods: large benches are cut into the rock in a descending spiral, and the broken rock is hauled out by trucks. Jwaneng in Botswana, one of the largest diamond mines in the world by value, operates as an open pit. As the pit deepens, the economics of hauling waste rock out of an ever-larger hole eventually tip in favour of underground methods, and many older pipes — including Udachny in Russia — have transitioned or are transitioning to underground extraction, typically using block caving or similar mass-mining techniques where the ore is induced to collapse into draw points below.

Alluvial and marine deposits are mined very differently. River gravels may be worked by mechanical excavators and simple washing plants. Marine deposits off the Namibian coast are recovered by purpose-built vessels that use suction or crawler systems on the seabed. These placer operations typically involve enormous volumes of sediment for relatively modest diamond recovery, because the stones, while dense, are scattered through a large body of material.

Grade in diamond mining is expressed in carats per hundred tonnes — a carat being one-fifth of a gram. A rich kimberlite pipe might carry several carats per hundred tonnes, while a poorer one may hold less than one. Even at the richer end, this means that several tens of tonnes of rock must be moved and processed to recover a single carat of diamond. The ratio of waste rock to ore, called the strip ratio in open-pit mines, can be very high by the later stages of a pit's life, which is a significant driver of operating cost and the reason transitions to underground mining become necessary.

What pulls on it

Industrial diamond's defining property is hardness. It is used wherever a material needs to be cut, ground, drilled, or polished and where conventional abrasives — silicon carbide, aluminium oxide — wear too quickly or leave too coarse a finish. The dominant use by volume is as abrasive grit and powder bonded into grinding wheels, cutting discs, drill bits, and wire saws. Stone processing — cutting granite, marble, and concrete — consumes large quantities. So does the machining of hard metals and ceramics, and the sharpening of other cutting tools. Polycrystalline diamond compacts, known as PCD, are made by sintering diamond powder under pressure and are used as cutting inserts for oil and gas drill bits and for machining non-ferrous metals. These applications together account for the great majority of industrial diamond consumption.

A smaller but technically significant demand stream comes from electronics. Diamond has thermal conductivity higher than any other material, a wide electronic band gap (meaning it resists breakdown at high voltages), and the ability to carry current when suitably doped. CVD diamond wafers are used as heat spreaders in high-power electronics and are under active development as a semiconductor substrate for power devices that operate at voltages and temperatures that would destroy silicon or even silicon carbide. This use is currently modest in volume but has attracted substantial research attention because the performance ceiling it could offer is substantially above what silicon-based devices can reach.

Demand for industrial diamond would change most sharply if the industries it serves changed their primary processes. A sustained reduction in construction and infrastructure activity would reduce demand for stone-cutting tools. A shift away from mechanical drilling in oil and gas towards other extraction methods would reduce demand for PCD drill bits. Conversely, broader adoption of diamond semiconductors in power electronics — for electric vehicles, grid inverters, or high-frequency communications — would pull demand toward the higher-purity CVD material rather than abrasive-grade grit. These two segments of the market are largely separate in terms of product specification and supply chain.

Turning ore into product Niveau 3

Once kimberlite ore is brought to surface, it must be broken down and the diamonds separated from the surrounding rock. The first stage is comminution — size reduction — but it requires care: diamond is hard but not tough, and aggressive crushing will shatter larger stones and destroy value. Modern kimberlite processing plants use autogenous milling (where the ore breaks itself) and scrubbing in rotating drums to disaggregate the softer clay-rich matrix without subjecting diamonds to high-impact crushing. The liberated material is then screened to remove fine particles that are too small to contain gem-sized or coarser industrial stones.

Separation of diamonds from the remaining mineral mix exploits two physical properties. First, diamond is denser than most gangue (waste) minerals, allowing a gravity concentration step using dense-media separation, in which the ore is immersed in a liquid of calibrated density so that heavy particles — including diamonds — sink while lighter minerals float. Second, diamond has a distinctive response to X-rays: it fluoresces under X-ray illumination, a property used in X-ray luminescence separators that detect and eject diamond-bearing particles from the stream using air jets. Grease tables, which exploit diamond's affinity for grease rather than water, were historically important but have largely been replaced by X-ray methods. Recovered diamonds are sorted by size, shape, and quality, with gem-quality material separated from industrial-grade and from material that will be crushed deliberately into grit or powder for abrasive use.

Synthetic diamond, which now accounts for the large majority of industrial supply, is produced by two routes. High-pressure, high-temperature synthesis (HPHT) replicates the geological process in a press using a carbon source, a metal solvent-catalyst, and a seed crystal, producing the grit and small stones used in most abrasive applications. Chemical vapour deposition (CVD) grows diamond as a film or thick plate from a carbon-containing gas on a substrate, at much lower pressures than HPHT; this route yields material with properties suited to electronics and precision optics. The reported production and reserve figures in the tables above cover natural mined diamond only; synthetic output is tracked separately and is not shown in those figures.

Substitution and recycling Niveau 3

For most abrasive applications, cubic boron nitride (CBN) is the principal alternative to diamond. CBN is the second hardest known material and is produced synthetically by the same HPHT presses used for diamond synthesis. It has one practical advantage over diamond in certain applications: diamond reacts chemically with iron at elevated temperatures, which limits its use in grinding ferrous metals, whereas CBN does not. For grinding hardened steels and cast iron, CBN is therefore often preferred on technical grounds rather than cost grounds. Silicon carbide and aluminium oxide remain in wide use for less demanding abrasive tasks, where their lower cost outweighs their shorter working life compared with diamond. The performance penalty of substituting a conventional abrasive for diamond is real and measurable — in tool life, surface finish, and cycle time — so substitution tends to happen only where the cost difference is large enough to justify it.

In the electronics application, the substitutes are the materials that current power semiconductor technology is built on: silicon, silicon carbide, and gallium nitride. Each occupies a different part of the performance space. Silicon is mature and inexpensive but limited in voltage handling and operating temperature. Silicon carbide and gallium nitride have extended the performance envelope considerably and are already in commercial production at scale. Diamond would extend it further still, but CVD diamond wafers at device-relevant quality and size remain expensive and the manufacturing ecosystem is not yet established. The question is not whether diamond is technically superior in this role — it is — but whether the cost of producing the material and building the device fabrication infrastructure around it can be brought down to a level where it competes with SiC and GaN on value, not merely on peak performance.

Recycling of industrial diamond is limited in scale. Diamond grit bonded into a grinding wheel or drill bit is consumed in use — worn away particle by particle — and is not recoverable in any practical sense. PCD tool inserts can in principle be reclaimed and reprocessed when the tool body is replaced, and some specialist recyclers do recover diamond from worn PCD and from diamond-bearing scrap, but the volumes are small relative to total supply. The practical barrier is not thermodynamics but economics: synthetic diamond grit is produced at sufficient scale and low enough cost that the collection, sorting, and reprocessing of used abrasive material rarely competes on price with new synthesis.