Lab-grown gems are materials created in a controlled laboratory environment that share the same chemical composition, crystal structure, and optical properties as their naturally occurring equivalents. These synthetic stones are chemically identical to their mined counterparts, such as a lab-grown diamond being pure carbon. This identity distinguishes lab-grown gems from simulants, like cubic zirconia, which only imitate the appearance of a natural stone but have a different underlying chemistry. Modern gem synthesis replicates geological processes that take millions of years, condensing them into weeks or months.
Creating Diamonds Through High Pressure and Vapor Deposition
Diamond synthesis relies on two distinct processes, both beginning with a small diamond seed crystal. The High-Pressure/High-Temperature (HPHT) method directly mimics the deep-earth conditions where natural diamonds form. This technique uses massive presses to create pressures of 5–6 GPa while heating the chamber to temperatures between 1,300 and 1,600°C.
A carbon source, typically high-purity graphite, is dissolved in a molten metal flux, often an alloy containing iron, nickel, or cobalt. This molten metal acts as a solvent-catalyst, allowing carbon atoms to transition from the graphite structure to the diamond structure. The carbon then migrates through the flux toward the cooler diamond seed crystal where it precipitates and crystallizes layer by layer over several days to weeks.
The second method, Chemical Vapor Deposition (CVD), uses a vacuum chamber at much lower pressures and temperatures, usually between 900 and 1,200°C. In this process, a diamond seed plate is placed inside the chamber, which is then filled with a carbon-containing gas along with hydrogen gas. An energy source, such as a microwave beam, breaks down the gas molecules into a plasma cloud of highly reactive carbon atoms.
These individual carbon atoms deposit onto the diamond seed crystal, bonding to its structure one atom at a time. Hydrogen gas is included to prevent the formation of non-diamond carbon, like graphite, during the process. This method allows the diamond to grow outward in layers, often over three to four weeks, resulting in a square, tabular crystal shape.
Growing Colored Gemstones: Melt and Solution Methods
Colored gemstones, such as corundum (ruby and sapphire) and beryl (emerald), are often grown using methods distinct from those used for diamonds. The Flame Fusion method is the oldest and most cost-effective technique, primarily used for synthetic corundum. This process involves finely powdered raw material, such as aluminum oxide, being slowly sifted through an inverted oxyhydrogen flame, which reaches temperatures around 2,200°C.
The powder melts into tiny droplets that fall onto a rotating pedestal, gradually crystallizing to form an elongated, carrot-shaped single crystal known as a boule. Color-causing elements, like chromium for red ruby or iron and titanium for blue sapphire, are mixed into the powder before melting. This fast method allows for growth rates of up to 10 millimeters per hour, creating a large crystal in only a few hours.
For gems that decompose when heated to their melting point, solution-based methods are employed, often resulting in higher quality stones. The Flux Growth method dissolves the gem’s chemical components, such as beryllium and aluminum for emerald, in a molten salt solution called a flux. The mixture is heated and then very slowly cooled over several months, allowing the crystal to precipitate out of the solvent.
The Hydrothermal Growth method mimics the natural geological process where hot, mineral-rich water dissolves and transports chemical components. In this technique, the raw materials are placed in a pressurized steel container, called an autoclave, along with a water-based solution and a mineralizer like sodium hydroxide. The chamber is heated to high temperatures and pressures, allowing the dissolved elements to recrystallize slowly onto a seed plate.
How Lab-Grown Gems Compare to Natural Stones
Lab-grown gems share the exact same chemical makeup and crystal lattice structure as their natural counterparts. The primary difference lies in the rapid, controlled environment of the laboratory, which leaves behind specific physical evidence. These telltale signs require specialized gemological equipment for positive identification.
For example, the extreme conditions of HPHT diamond growth can sometimes trap microscopic metallic remnants from the nickel, iron, or cobalt flux within the crystal structure. CVD diamonds, grown layer by layer, may exhibit distinct growth sectors or planar layers that differ from the typical octahedral growth patterns seen in natural diamonds. These subtle structural variations are a direct consequence of the accelerated growth rate.
Colored gems grown by the Flame Fusion method often contain curved growth lines, or striae, which are visible under magnification. These curves contrast sharply with the straight, angular growth zones found in natural corundum. Solution-grown gems, like flux emeralds, may contain tiny pockets of trapped flux, while hydrothermal emeralds can show characteristic inclusions of the water-based growth solution.