Lab-created gemstones are materials grown in a controlled environment that share the exact same chemical, physical, and optical makeup as their natural counterparts. These manufactured stones replicate the geological processes that form gems deep within the Earth, but condense the time frame into weeks or months. By supplying the necessary raw materials and precisely controlling the environment, scientists can produce gems that are identical to those found in a mine. The difference between a stone formed in the laboratory and one formed in the earth is solely its origin.
Defining Lab-Created Gemstones
A “synthetic” or “lab-grown” gemstone possesses the identical crystal structure, chemical composition, and physical properties as the natural material it mimics. For example, a synthetic diamond is composed of pure carbon atoms arranged in the same isometric crystal lattice as a mined diamond.
This is distinctly different from a “simulant,” which only looks like a natural gem but is made of a completely different material. Common simulants include cubic zirconia and moissanite, which are often used to imitate diamond but lack the same chemical fingerprint. Synthetic gems are created from the same raw material elements found in nature, grown under conditions engineered to be conducive to crystallization.
High-Temperature Synthesis Methods
One of the earliest methods for growing synthetic gems is the Verneuil process, also known as flame fusion. This technique is primarily used to create corundum, including synthetic rubies and sapphires. It involves dropping finely powdered aluminum oxide through a high-temperature oxyhydrogen flame, which can exceed 2,000°C, melting the powder into liquid droplets.
These droplets land on a rotating seed crystal, solidifying layer by layer to form a single, carrot-shaped crystal known as a boule. The Verneuil method is fast and relatively inexpensive. However, the rapid cooling often introduces internal stresses, gas bubbles, and distinctive curved growth lines, or striae, visible under magnification.
A more refined high-temperature technique is the Czochralski pulling method, which produces exceptionally high-quality synthetic corundum, alexandrite, and garnet. This process involves melting the raw material within a high-purity crucible at temperatures near the material’s melting point. A small seed crystal is then lowered until it just touches the surface of the melt.
As the seed is slowly rotated and simultaneously pulled upward, the molten material crystallizes onto the seed, forming a large, flawless single crystal. The slow, controlled pulling rate allows for the growth of highly pure crystals that exhibit superior optical homogeneity. This method is slower and more expensive than the Verneuil process, but it yields material with fewer internal defects and a more natural crystal shape.
High-Pressure and Solution-Based Growth
For materials that naturally form under extreme subterranean conditions, like diamonds, the High-Pressure/High-Temperature (HPHT) method is used to recreate the Earth’s deep mantle environment. This process involves placing a small diamond seed crystal into a growth cell surrounded by a carbon source, such as graphite, and a metal solvent-catalyst.
The apparatus is subjected to immense pressure, around 5.5 GigaPascals, and temperatures between 1,300°C and 1,600°C. Under these conditions, the metal solvent melts and dissolves the carbon source, allowing the carbon atoms to slowly migrate and crystallize onto the cooler diamond seed. This results in a stone that is chemically and physically identical to its mined counterpart.
For gemstones that naturally form in the presence of water, such as emeralds and quartz, the Hydrothermal Growth method is employed. This process takes place within a heavy-walled steel vessel called an autoclave, designed to withstand extremely high internal pressures. Raw nutrient materials are placed in the autoclave along with a solvent, often superheated water containing a mineralizing agent.
The autoclave is heated, creating distinct temperature zones that drive convection currents. Nutrients dissolve in the hotter zone and then precipitate onto a seed crystal in the cooler zone. This method operates at lower temperatures and pressures than HPHT and is far slower, often taking several months. The result is a synthetic crystal that incorporates small amounts of water, closely mimicking the internal characteristics of natural, water-formed gems.
Comparing Lab-Grown and Natural Gems
From a scientific perspective, lab-grown synthetic gemstones and their natural equivalents are the same material, sharing identical chemical formulas, hardness, and refractive indices. The primary differentiating factor is the time scale and the conditions of their formation.
This difference in origin leaves behind unique internal signatures that trained gemologists use for identification. For instance, the rapid growth of Verneuil stones often leaves trapped gas bubbles and curved color bands, whereas natural gems display straight or angular color zoning. HPHT diamonds may contain microscopic metallic inclusions from the solvent-catalyst used in their growth.
Lab-grown stones typically exhibit higher clarity and fewer imperfections than their natural counterparts because the growth environment is pristine and controlled. Natural gemstones often contain inclusions, or internal flaws, that reflect the chaotic environment where they formed. Synthetic gems offer consumers a high-quality, chemically identical alternative at a lower cost than comparable natural stones.