“Is it real?” is the question most people ask about a laboratory-grown diamond, and it mixes two separate questions. One is what the stone is made of. The other is how it has to be described when it is sold. US rules answer both, in the Federal Trade Commission’s Guides for the Jewelry, Precious Metals, and Pewter Industries, 16 CFR Part 23. This guide sets out what those rules say. It does not compare prices, and it does not suggest which kind of stone anyone should choose.
What a diamond is, by definition
Section 23.12(a) defines a diamond as “a mineral consisting essentially of pure carbon crystallized in the isometric system”. The definition also gives the properties that follow from that structure: a hardness of 10, a specific gravity of about 3.52 and a refractive index of 2.42.
Nothing in the definition mentions where or how the crystal formed. A stone grown in a laboratory that is carbon crystallised in the isometric (cubic) system meets it, just as a mined stone does. In that physical sense the answer to the question is yes. A laboratory-grown diamond is diamond. It is not an imitation of one.
That is what separates lab-grown diamond from simulants. Cubic zirconia and moissanite look similar, but they are different materials with different properties, and the moissanite vs diamond guide sets out how they differ. A diamond’s defining figures can be compared directly: the Mohs hardness scale, the refractive index chart and the specific gravity chart each place diamond among other gems.
What the seller has to disclose
The same section limits how the word can be used. Section 23.12(b) makes it unfair or deceptive to use the unqualified word “diamond” for a product that does not meet the definition, or that lacks at least 17 polished facets arranged symmetrically. Unqualified means the word on its own, with nothing before it.
For stones grown in a laboratory, the Guides require the origin to be disclosed. Section 23.25(b) covers laboratory-grown, laboratory-created and “[manufacturer name]-created” products. A gemstone name used for such a product must be preceded, with equal prominence, by a word that clearly discloses that the product is not a mined stone. In practice that means descriptions such as “laboratory-grown diamond” or “laboratory-created diamond”.
Section 23.25(c) adds a limit in the other direction. Words such as “laboratory-grown”, “laboratory-created” and “synthetic” may be used with a natural stone’s name only for a product that has essentially the same optical, physical and chemical properties as the stone named. A simulant cannot be called a “lab-created diamond”. It is not diamond, so it has to be described as an imitation or simulant.
The word “cultured”
Section 23.12(c)(3) allows “cultured” to describe laboratory-created diamonds that have essentially the same optical, physical and chemical properties as mined diamonds. The word may not stand alone. It must be accompanied by a clear and conspicuous disclosure, such as “laboratory-created”, “laboratory-grown” or “[manufacturer name]-created”, conveying that the product is not a mined stone. So “cultured diamond” on its own is not enough under the Guides.
“Imitation”, “simulated” and “faux”
A stone that only imitates diamond has to be identified as such. Section 23.25(b) requires the word “imitation” or “simulated” to be placed immediately before the stone’s name, with equal prominence. A note to the section adds that “faux” is not an adequate disclosure that a stone is not mined.
“Real”, “genuine” and “natural”
Section 23.27 makes it unfair or deceptive to use “real”, “genuine”, “natural”, “precious”, “semi-precious” or similar words for an industry product that is manufactured or produced artificially. That is why the marketing vocabulary around lab-grown diamonds is careful. The stone is diamond, but it was produced artificially, so those particular adjectives are restricted.
“Brilliant” and “full cut”
One more rule applies to every diamond, whatever its origin. Section 23.17 restricts the unqualified terms “brilliant”, “brilliant cut” and “full cut” to round diamonds with at least 32 facets plus the table above the girdle and at least 24 facets below it. Other shapes that meet the same facet counts may use the terms only with the shape disclosed alongside, as in “emerald-shaped brilliant”.
How you tell them apart
Because laboratory-grown and mined diamonds share the defining properties, tests that measure those properties, such as a refractive index reading or a specific gravity test, give diamond readings either way. Establishing the origin needs a gemmological laboratory with specialist equipment, and a laboratory report states when a diamond has been identified as laboratory-grown. The guide to diamond grading reports explains what a report records and how to check that it belongs to the stone.
The rules above are US rules. Other countries have their own trading standards and terminology, and this guide does not cover them. Nor does it say anything about value. Weight and size are measurable, and the diamond size calculator relates carats to millimetres for any diamond. What a particular stone sells for is a market question, not a definition.