Lab-grown diamonds, also known as synthetic or laboratory-created diamonds, are chemically and physically identical to natural diamonds. They are formed within a controlled environment instead of deep within the Earth, possessing the exact same carbon-atom crystal structure and optical properties as mined diamonds. Diamonds are “grown” using two primary technological methods that replicate natural conditions: High-Pressure/High-Temperature (HPHT) and Chemical Vapor Deposition (CVD).
Creating Diamonds Using High-Pressure/High-Temperature
The HPHT method is the older technique that directly mimics the extreme environment where natural diamonds form in the Earth’s mantle. This process requires massive machinery, such as cubic presses or BARS apparatuses, to generate the necessary conditions. A small diamond seed crystal, typically 0.5 to 2 millimeters in size, is placed into a central growth cell alongside the carbon source.
The carbon source is usually high-purity graphite, placed near the seed crystal. A metal solvent-catalyst, often an alloy of iron, nickel, or cobalt, is also introduced into the cell. The system is then subjected to extreme conditions, including pressure ranging from 5 to 6 GigaPascals (GPa) and temperatures between 1,300°C and 1,600°C.
Under this intense heat and pressure, the metal catalyst melts and dissolves the graphite carbon. The dissolved carbon then migrates through the molten metal to the cooler diamond seed crystal. The carbon atoms precipitate out of the solution and crystallize onto the seed, slowly building the diamond layer by layer over several weeks. This process is highly energy-intensive due to the need to maintain the pressure and temperature within the growth chamber.
Creating Diamonds Using Chemical Vapor Deposition
The CVD method represents a modern approach to diamond synthesis, relying on a chemical reaction rather than extreme physical force. This process takes place in a vacuum chamber at lower pressures and temperatures compared to HPHT. Inside the chamber, a substrate plate holds numerous small diamond seed crystals.
The chamber is heated to a temperature between 700°C and 1,200°C and then filled with a mixture of hydrocarbon gases, such as methane, and hydrogen. Microwaves or other energy sources are used to activate and break down the gas molecules, creating a plasma cloud. The energy from the plasma breaks the molecular bonds of the gases, allowing pure carbon atoms to separate and deposit.
The freed carbon atoms deposit onto the seed plate, bonding to the diamond crystals layer by layer. The presence of hydrogen is crucial as it preferentially etches away any non-diamond carbon (graphite) that attempts to form, ensuring the final crystal structure is pure diamond. This technique often produces plate-like crystals and provides greater control over the chemical environment, which influences the diamond’s final properties.
Structural Differences and Identification of Grown Diamonds
Although lab-grown diamonds are chemically identical to natural diamonds, differences in their growth environments result in distinctive structural features that allow gemologists to determine their origin. HPHT diamonds grow outward in all directions, typically exhibiting cuboctahedral crystal structures with geometric growth sectors. The HPHT process means these diamonds often contain microscopic metallic inclusions from the iron, nickel, or cobalt catalyst used.
These metallic inclusions are opaque and can cause the HPHT diamond to be weakly magnetic, a property not found in natural diamonds. HPHT diamonds frequently incorporate nitrogen from the growth environment, which can lead to a yellowish hue and a distinctive cross-shaped fluorescence pattern under short-wave UV light.
In contrast, CVD diamonds grow in a single, vertical direction, resulting in a distinct layered structure sometimes observed as parallel striations under high magnification. While CVD diamonds do not have metallic inclusions, they may contain non-diamond carbon inclusions, such as dark graphite, or exhibit a brownish tint that often requires a post-growth HPHT treatment to remove. Advanced gemological laboratories use equipment like DiamondView imaging and photoluminescence spectroscopy to analyze these unique growth patterns, fluorescence colors, and inclusion types to identify the diamond’s creation method and confirm its laboratory origin.