Lab-grown diamonds are real diamonds made in a factory instead of a mine. They have the same carbon crystal structure, hardness and optical properties as natural diamonds, so they cannot be told apart by eye or with ordinary jeweler's tools. Producers grow them by two methods, high pressure high temperature (HPHT) and chemical vapor deposition (CVD), and gem labs identify them with spectroscopy and imaging.
Lab-grown versus simulants
A lab-grown diamond is diamond: crystalline carbon with the same structure and properties as a mined stone. A simulant only imitates diamond's appearance and is a different material. Cubic zirconia, moissanite, white sapphire and glass are simulants.
Lab-grown diamonds are also called laboratory-created, laboratory-grown, man-made or synthetic diamonds. "Synthetic" is the term gemologists have long used, and it means the stone was made by people, not that it is fake.
A short history
Scientists tried to make diamond for more than a century before anyone succeeded reliably. A team at General Electric in the United States, including Tracy Hall, produced diamond from graphite in December 1954 using a high-pressure apparatus called the belt press. GE announced the result in 1955, and its process became the basis for industrial diamond manufacture. A Swedish team at ASEA had made diamond in 1953 but did not publish at the time.
Those first stones were tiny and suitable only for abrasives. GE grew the first gem-quality crystals, about a carat in size, around 1970, but the process was too costly to compete with mined stones. Over the following decades, producers in several countries refined HPHT presses and growth methods.
CVD growth developed alongside, with research from the 1950s through the 1980s in the United States, the Soviet Union and Japan. Gem-quality CVD stones reached the jewelry market in the 2000s. By the late 2010s, both methods were producing colorless stones of a carat and larger in commercial quantities.
How HPHT growth works
HPHT reproduces the conditions in the mantle where natural diamonds form, explained on the diamond geology page. A press squeezes a growth cell to pressures around 5 to 6 gigapascals and heats it to roughly 1,300 to 1,600 degrees Celsius.
Inside the cell, a carbon source such as graphite dissolves in a molten metal solvent, usually a mix of iron, nickel or cobalt. The carbon moves through the molten metal and crystallizes on a small diamond seed. Growth takes days to weeks, depending on the size and quality wanted.
Producers use three main press designs: the belt press, the cubic press (with six anvils pressing from all sides) and the split-sphere or BARS press. HPHT crystals usually grow in a cuboctahedral shape, combining cube and octahedron faces, which differs from the octahedral shape typical of natural diamond.
Nitrogen from the air or the cell gets into most HPHT diamonds and makes them yellow. Producers add nitrogen "getters" to the cell to grow colorless stones, and add boron to grow blue ones.
How CVD growth works
CVD builds diamond from a gas at low pressure. Thin diamond seed plates sit in a vacuum chamber filled with a mix of hydrogen and a small amount of methane. Microwave energy or another source heats the gas into a plasma at several thousand degrees, breaking the molecules apart. Carbon atoms then settle onto the seed plates and bond into the diamond lattice, layer by layer.
CVD crystals grow as flat, square-sided blocks. Many come out brownish and are treated after growth with HPHT annealing or other processes to improve color. Most CVD diamonds contain almost no nitrogen and are Type IIa, a type that is rare among natural diamonds. The diamond chemistry and formation page explains diamond types.
Same properties as natural diamond
Lab-grown and natural diamonds share every property that matters for wear and appearance.
| Property | Natural and lab-grown diamond |
|---|---|
| Chemistry | Carbon |
| Crystal system | Cubic |
| Mohs hardness | 10 |
| Refractive index | 2.417 |
| Dispersion | 0.044 |
| Specific gravity | 3.52 |
Because thermal conductivity is the same, standard handheld diamond testers read lab-grown stones as diamond. Some HPHT stones contain metallic inclusions that make them weakly magnetic, which a strong magnet can detect, but that is a clue, not a test.
How labs detect lab-grown diamonds
Identifying a lab-grown diamond takes laboratory equipment. Gem labs rely on several lines of evidence:
- Growth patterns. HPHT stones grow in cube and octahedral sectors, while CVD stones grow in layers. Deep ultraviolet imaging, such as the DiamondView instrument developed by De Beers researchers, shows these patterns as fluorescence images.
- Spectroscopy. Infrared spectroscopy reveals diamond type and nitrogen behavior. Photoluminescence spectroscopy detects defects such as silicon-vacancy centers that are common in CVD stones.
- Inclusions. HPHT stones may contain metallic flux inclusions. CVD stones may show dark pinpoints of non-diamond carbon.
- Strain. Viewed between crossed polarizers, natural diamonds usually show irregular strain patterns, while many lab-grown stones show different, more regular patterns.
Screening instruments built for the trade can sort large numbers of small diamonds and refer suspect stones for full testing. The how to tell if a diamond is real guide explains why home tests cannot make this separation, and the diamond grading labs page covers who issues reports.
Grading and reports
Gem labs issue reports for lab-grown diamonds that state clearly that the stone is laboratory-grown. Many labs describe their color and clarity using the same terms as for natural stones, though reports for lab-grown diamonds have changed format over the years and differ from lab to lab. Reports also note post-growth treatments such as HPHT processing. The diamond certificates guide explains how to read a report.
Disclosure and the FTC Jewelry Guides
In the United States, the Federal Trade Commission's Guides for the Jewelry, Precious Metals, and Pewter Industries set out how sellers should describe diamonds. The FTC revised the Guides in 2018. The revised definition of diamond dropped the word "natural," which acknowledged that a lab-grown diamond has the same composition and structure as a mined one.
The Guides still require clear disclosure. Sellers must not describe a lab-grown diamond as a "diamond" without a qualifier. Acceptable qualifiers include "laboratory-grown," "laboratory-created" and "[manufacturer name]-created," and the revised Guides no longer list "synthetic" among the suggested terms. Terms that could suggest a mined origin, such as "cultured," need clear qualification. Other countries have their own rules, and trade bodies such as CIBJO publish nomenclature standards.
How pricing has changed
Lab-grown diamonds started out priced only modestly below natural stones. As production expanded through the late 2010s and 2020s, their prices fell sharply, and the gap between lab-grown and natural diamonds of similar grades widened a great deal. Because lab-grown supply is not limited by geology, resale value for lab-grown stones tends to be low. The diamond pricing page covers how diamonds are priced.
Uses beyond jewelry
Most synthetic diamond by weight goes to industry, not jewelry. Grit and small crystals are used in cutting, drilling, grinding and polishing tools, including the wheels that polish gem diamonds. CVD diamond also has uses in optics, heat spreaders for electronics and other technical fields, thanks to its hardness and thermal conductivity.
Frequently asked questions
Are lab-grown diamonds real diamonds?
Yes. They have the same chemistry, crystal structure and physical properties as mined diamonds. They are not simulants.
Can a jeweler tell a lab-grown diamond from a natural one?
Not with a loupe or a standard diamond tester. Identification needs laboratory instruments, though a laser inscription on the girdle may state the origin.
What is the difference between HPHT and CVD diamonds?
HPHT diamonds grow from molten metal under high pressure and heat. CVD diamonds grow layer by layer from carbon-rich gas at low pressure.
Do lab-grown diamonds test as diamond?
Yes. Thermal and most electrical testers identify them as diamond, since their properties are identical.