A reliable grading report (e.g. from GIA, HRD, AGS, or IGI) will confirm that your diamond is natural.

From Hedda T. Schupak, JCK Editor-in-Chief in JCK-Jewelers Circular Keystone -- 4/3/2005

"Detection of synthetic diamonds is no longer a concern for the jewelry industry. That was a key good-news message presented by Dr. James Shigley, director of research for the Gemological Institute of America, during GIA's GemFest Basel, part of the BaselWorld 2005 trade fair.

Synthetic diamonds first became a concern in 1970, when General Electric launched its first attempt at them, but the issue has come to the fore again in the past few years with the advent of several new producers and an article touted synthetics on the cover of Wired magazine.

But there is no known commercial production of colorless synthetics, said Shigley. Furthermore, synthetic diamonds have a unique crystal morphology due to how they're grown in a laboratory. Their growth process produces a distinct color zoning feature that gives the stones identifying characteristic. They also have a distinct graining pattern and sometimes have metallic inclusions left from the flux used in the growing process.

In addition, diamonds produced by carbon vapor deposition don't pose a threat to the market, he said. To date, all specimens GIA has seen from CVD producer Apollo were under a carat, and the process produces light brown stones, requiring further (HPHT) treatment to lighten them.

There may in the future be a joining of the two methods, whereby a CVD diamond is grown on a synthetic diamond substrate, but these stones would also be detectable, Shigley said."

Synthetic diamonds made by Gemesis are bright colours like yellow and spartan green. 

For further information see Diamonds Glossary.