Diamond is composed of carbon atoms arranged in a crystalline structure, making it the hardest naturally occurring substance on Earth. The journey a diamond takes, from its formation deep within the planet or its creation in a laboratory, to its eventual appearance in the market is complex. Understanding the sourcing of diamonds involves exploring both the ancient geological processes that create natural stones and the modern technological advancements that offer an alternative supply.
The Geological Origins of Natural Diamonds
Natural diamonds originate under conditions of extreme heat and pressure far beneath the Earth’s surface, in a zone known as the diamond stability field. These conditions are typically met in the upper mantle, at depths ranging from 150 to 250 kilometers below ancient continental landmasses called cratons. Temperatures hover between 900°C and 1,400°C, combined with pressures of approximately 50 to 80 kilobars, allowing carbon atoms to bond into the signature diamond crystal structure.
The diamonds remain stable in the mantle for billions of years until a rare geological event brings them closer to the surface. They are transported rapidly by deep-source volcanic eruptions that create vertical, carrot-shaped columns of rock known as kimberlite and, more rarely, lamproite pipes. The rapid ascent prevents the diamonds from turning back into graphite, preserving them within the igneous host rock.
Methods of Physical Extraction
The extraction of natural diamonds is categorized based on whether the stones are recovered directly from their host rock or from secondary deposits. Primary source mining targets the kimberlite and lamproite pipes directly, using methods like open-pit or underground mining. Open-pit operations involve removing layers of rock and soil above the pipe before blasting the ore inside the exposed pit. As the pipes descend, underground mining takes over, often employing block caving where ore is blasted from upper tunnels and collected in lower tunnels for transport to the surface.
Secondary source mining focuses on diamonds that have been naturally weathered and transported away from the primary pipes by water. Alluvial mining recovers diamonds from riverbeds, beaches, or ancient gravel deposits. A specialized form is marine mining, which uses powerful crawlers on ships to vacuum diamond-bearing gravel from the seabed, sometimes hundreds of meters offshore.
Once the ore or gravel is collected, it undergoes a recovery process to isolate the diamonds. The material is first crushed and scrubbed to reduce its size and remove waste. It is then subjected to dense media separation (DMS), where it is mixed with a heavy liquid slurry that causes the denser diamonds to sink while the lighter rock floats. Final recovery stages often employ X-ray sorting, which uses the natural fluorescence of diamonds under X-rays to trigger an air blast that separates the stone from other heavy minerals.
Alternative Sourcing: Synthesized Diamonds
In addition to mining, a growing number of diamonds are sourced from laboratories, where they are grown using two primary methods that replicate the natural formation process. One technique is High-Pressure/High-Temperature (HPHT) synthesis, which mimics the conditions deep inside the Earth. This process begins with a small diamond seed crystal placed in a growth cell alongside a carbon source, typically graphite, and a metal solvent-catalyst. The cell is subjected to extreme conditions, generally 5–6 GPa of pressure and temperatures between 1,300°C and 1,600°C. The carbon dissolves into the molten metal catalyst and precipitates onto the seed crystal, forming a new diamond layer over a period of days or weeks.
The second major method is Chemical Vapor Deposition (CVD), which operates under lower pressure and temperature. A diamond seed is placed in a vacuum chamber, which is then filled with a carbon-containing gas, commonly methane, and hydrogen. The chamber is heated to temperatures around 600°C to 1000°C, and the gases are ionized into a plasma. The carbon atoms separate from the gas and deposit onto the seed, crystallizing into a diamond structure. Both the HPHT and CVD processes create diamonds that are chemically, physically, and optically identical to their natural counterparts, differing only in their origin.
Ensuring Responsible Supply Chains
The sourcing of diamonds is governed by global initiatives designed to ensure the stones entering the market are ethically sourced. The most significant framework is the Kimberley Process Certification Scheme (KPCS), established in 2003 by the United Nations, governments, and the diamond industry.
The KPCS was created to address “conflict diamonds,” defined narrowly as rough diamonds used by rebel movements to finance wars against legitimate governments. The certification scheme requires that every shipment of rough diamonds traded between participating countries must be sealed in tamper-proof containers and accompanied by a government-validated Kimberley Process Certificate. This certificate attests that the diamonds are conflict-free, offering a baseline assurance of ethical origin.
The system works by restricting trade only among participating member countries, of which there are over 80, representing almost all global rough diamond production. This regulatory framework creates a transparent and verifiable chain of custody from the mine site to the point of export. By mandating this documentation, the KPCS ensures that diamonds are tracked as they move through the supply chain, preventing illicit stones from entering the legitimate market.