Are lab-grown diamonds considered fake?
Quick answer
No. Lab-grown diamonds are real diamonds, not simulants like cubic zirconia or moissanite. They are the same chemical composition, the same crystal structure, the same hardness and the same optical properties as mined diamonds, and the FTC formally classifies them as real diamonds. The only difference is where they were formed.
What the FTC actually said in 2018
The FTC revised its Jewelry Guides in 2018 and removed the word "natural" from the official definition of a diamond, which had previously read "a natural mineral consisting essentially of pure carbon crystallized in the isometric system." Lab-grown stones now meet the FTC's definition of a diamond. Sellers still have to disclose origin with terms like "laboratory-grown" or "lab-created"; the stone cannot be sold as just "diamond" without that qualifier.
Where the real simulants sit
Cubic zirconia and moissanite are diamond simulants, not diamonds. Cubic zirconia is zirconium dioxide, sits at Mohs 8 to 8.5 and has a different refractive index. Moissanite is silicon carbide, sits at Mohs 9.25 and shows a distinctive doubling effect through the table. Both can be separated from diamond with a basic thermal or electrical conductivity tester in seconds. Lab-grown diamond passes every one of those tests as a diamond, because it is one.
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