How a Diamond Forms: from the Earth to the Jewellery Case

At a gemstone market in India, a gemmologist lifts a rough diamond to the light. The octahedral crystal, translucent and matte, looks nothing like the brilliance we know. Three billion years beneath the earth's surface, a violent volcanic rise, then weeks of cutting precise to the micron: this is a diamond's journey, from the mantle to your jewellery box.

This guide traces the diamond's geological formation, its extraction, its transformation, and its journey to our workshops. From carbon under pressure to the quality standards we apply, it follows every stage, from crystallisation deep in the mantle to the final setting.

The diamond forms between 150 and 200 kilometres beneath the earth's surface, in the upper mantle. At this depth, conditions reach 45 to 60 kilobars of pressure (equivalent to 45,000 to 60,000 times atmospheric pressure) and 900 to 1,300 °C. These extreme parameters allow carbon atoms to organise into a cubic crystalline structure, the densest and most stable known.

The process is slow. One to three billion years separate the initial crystallisation from the ascent to the surface. The diamonds we set today formed long before the first multicellular organisms appeared on Earth.

A common misconception: does diamond come from coal? No. Coal forms from organic matter buried at shallow depths (a few kilometres), under conditions of far lower pressure and temperature. Diamond crystallises from mantle carbon, often of primordial origin, carbon trapped during the formation of the Earth, which has never reached the surface.

The majority of diamonds crystallise in the upper mantle under high pressure, but three distinct geological environments produce natural diamonds:

• Classic mantle crystallisation (150–200 km): the primary source. Carbon dissolved in the mantle concentrates and crystallises slowly under constant pressure.
• Subduction diamonds (up to 700 km): formed when an oceanic plate plunges beneath a continental plate, carrying surface carbon to great depths. Rare, often small, and sometimes bearing unique mineral inclusions.
• Meteorite impact diamonds: the collision of an asteroid with the Earth generates a shockwave capable of transforming graphite into diamond within seconds. These diamonds, microscopic and poorly crystallised, hold no interest for jewellery, but confirm that high pressure alone is sufficient, even without elevated temperature.

A diamond formed 200 kilometres deep would never naturally reach the surface: pressure decreases on the way up, and the diamond structure becomes unstable above 150 kilometres. It requires a fast, violent lift: a kimberlite volcanic eruption.

Kimberlite rises in a matter of hours from the upper mantle to the surface, at estimated speeds of between 10 and 30 metres per second. This velocity prevents the diamond from reverting to graphite, its stable form at low pressure. A slow ascent would destroy it.

The eruption forms a vertical volcanic conduit, known as a kimberlite pipe. The magma cools at the surface, trapping diamonds within a dark, often altered rock rich in olivine and mantle minerals. Some pipes contain a few carats per tonne of rock; others contain none at all.

Kimberlite takes its name from Kimberley, in South Africa, where the first large-scale industrial diamond mines were sunk in the nineteenth century. It is an ultrabasic volcanic rock, rare by nature, which forms only beneath ancient, stable mantle zones known as cratons.

Lamproite, a related rock, plays the same role in certain regions, most notably Australia and the Argyle mine. Chemically distinct, it also carries diamonds up from the mantle. Both rocks share one defining characteristic: an ultra-rapid ascent from the diamond-bearing zone.

Diamonds are not found everywhere. Only ancient, stable geological zones, Archaean cratons, preserve the mantle conditions required for their formation and preservation.

The world's principal deposits are concentrated in southern Africa (Botswana, South Africa, Namibia), Russia (Yakutia, the Urals), Canada (the Northwest Territories), Australia (the Kimberley region and the now-closed Argyle mine), and Angola. Each region produces diamonds with distinct characteristics: colour, inclusions, and average crystal size.

The Diamonds we select for our creations come predominantly from certified mines in Botswana and Canada, two sources widely recognised for their traceability and responsible practices. Every stone undergoes gemological assessment before setting.

Our comprehensive guide details the world's major producing regions, the history of their discoveries, and the challenges of contemporary supply chains.

Once kimberlite ore has been extracted, it is crushed and washed to separate the diamonds from the surrounding rock. Diamond, being denser (3.52 g/cm³) than kimberlite, is concentrated through gravimetric processes and flotation in dense liquids.

Optical sorting follows: rough diamonds are exposed to X-rays. Under this radiation, diamond emits a characteristic blue fluorescence, detected by sensors that trigger a jet of air to isolate each stone from the flow. This automated sorting process handles several tonnes of concentrate per hour.

The recovered crystals are then classified according to their size, shape, colour, and clarity. Fewer than 20% of extracted diamonds reach gem quality. The remainder is directed toward industrial applications: cutting tools, drill bits, abrasives, and polishing.

A rough diamond is matte and translucent. Its brilliance comes entirely from the cut, which transforms light into fire and scintillation. The modern round brilliant cut, developed in the early twentieth century, maximises light return through total internal reflection: light enters through the crown, bounces off the pavilion facets, and exits toward the eye in flashes of white and spectral colour.

The cutting process begins with microscopic analysis and three-dimensional imaging of the rough stone. The cutter determines how many stones can be yielded, their crystallographic orientation, and the best approach to minimising visible inclusions. A poor decision results in weight loss with no gain in quality.

Initial cleaving divides the rough into sections. Laser sawing shapes the blanks. Bruting establishes the overall form. Then comes faceting: each facet is polished individually on a disc coated with diamond powder, the only abrasive capable of polishing a diamond.

Weight loss is considerable. A rough diamond of 1 carat yields on average 0.4 to 0.6 carats once cut. On exceptional stones, the loss can reach 60% in order to preserve a remarkable inclusion or maximise colour.

Once cut, the diamond is evaluated according to four criteria standardised by the GIA (Gemological Institute of America): Carat, Cut, Color, Clarity, the 4Cs.

• Carat (weight): a metric unit of 0.2 grams. A 1-carat diamond weighs exactly 0.2 g. Prices evolve in a non-linear fashion: a 2-carat diamond costs more than twice the price of a 1-carat diamond of equal quality.
• Cut: the quality of the cut. An excellent cut returns 90% of light toward the eye. A poor cut, even on a flawless stone, reduces brilliance by half.
• Color: a scale from D (colourless) to Z (perceptible yellow). D, E, and F diamonds are considered colourless. G, H, and I are near-colourless, impossible to distinguish once set. Beyond K, the yellow tint becomes visible.
• Clarity: the presence of internal inclusions or surface blemishes. The scale runs from FL (flawless, no inclusions visible under 10x magnification) to I3 (inclusions visible to the naked eye). VS1 and VS2 diamonds (very slightly included) offer an excellent price-to-quality ratio: clean to the eye, yet less costly than VVS grades.

The diamonds we set meet strict standards: excellent to very good cut, minimum G colour, minimum VS2 clarity. Each stone undergoes individual inspection before setting.

The final stage transforms the cut stone into a piece of jewellery. The setting secures the diamond onto its metal mount, 18K yellow gold or Platinum in our creations, ensuring both mechanical hold and optical enhancement.

The prong setting lifts the stone above the metal, maximising the entry of light through the sides and pavilion. This is the classic setting for solitaires and engagement rings. The prongs, four or six in number, hold the diamond by the girdle. Their thickness depends on the weight of the stone: the heavier the diamond, the more robust the prongs must be.

The bezel setting surrounds the stone with a collar of metal. It offers greater protection to the edges of the diamond, making it ideal for everyday wear, though it slightly reduces brilliance by blocking lateral light. We use it on certain wedding rings and on small diamond pavé arrangements.

The channel setting aligns several diamonds side by side, held in place by two parallel metal rails. This is the setting used for pavé wedding rings and our multi-stone creations. The visual continuity brings out the collective fire of the stones.

The choice of setting depends on the design, the intended use, and the size of the diamond. Our gemologists adapt the technique to each creation to guarantee lasting durability and maximum brilliance.

Beyond its exceptional physical properties, a hardness of 10 on the Mohs scale and a refractive index of 2.42, the diamond carries a universal symbolic weight.

The stone of commitment since the 15th century, it has embodied the permanence and solidity of a promise. Its resistance to wear and its rarity make it the material of choice for wedding rings and engagement rings across most Western cultures.

In traditional Indian lithotherapy (not scientifically recognized), the Diamond is associated with the planet Venus and the higher chakras. These beliefs have no gemological basis, yet they reflect the deep and longstanding connection between this stone and the notions of mental clarity and purity of intention.

We explore these symbolic and cultural dimensions in a dedicated article, drawing clear distinctions between tradition, gemology, and the history of fine jewellery.

The Diamond industry has long been associated with opaque practices and conflict zones. Since 2003, the Kimberley Process has governed the international trade of rough Diamonds to prevent stones from war zones from financing armed groups.

This system relies on certificates of origin accompanying each batch of exported rough Diamonds. More than 80 countries participate. Despite its limitations, as the process does not cover working conditions or environmental impact, it has significantly reduced the circulation of conflict Diamonds.

Our commitment: we work exclusively with suppliers certified by the Kimberley Process and prioritize Canadian and Botswanan sources, recognized for their enhanced traceability. Every Diamond we set can be traced back to its mine of origin.

Traceability standards, available certifications, and emerging alternatives, including lab-grown Diamonds, are covered in a comprehensive guide we have published to support your choices.

From mantelic crystallization under extreme pressure to the millimetric cut that reveals its fire, the Diamond travels an exceptional geological and technical journey. Three billion years, a volcanic ascent lasting just a few hours, then weeks of human craftsmanship: this process makes the Diamond the hardest and most sought-after precious stone in the world.

Our Diamond-set creations meet strict quality criteria: excellent cut, minimum G color, VS2 clarity, and rigorous traceability from mine to workshop. Each stone undergoes individual gemological inspection before setting.

To explore the world of Diamonds further, including quality criteria and gemological certifications, we have gathered all of our expertise in a comprehensive reference guide.