The Federal Trade Commission’s Guide for the Jewelry, Precious Metals and Pewter Industries

FTC writes:

23.24 Misuse of the words "real," "genuine," "natural," "precious," etc.

It is unfair or deceptive to use the word "real," "genuine," "natural," "precious," "semi-precious," or similar terms to describe any industry product that is manufactured or produced artificially.

More info @ http://www.ftc.gov/bcp/guides/jewel-gd.htm