Internet auction site eBay has tightened its rules on how sellers can describe diamonds and diamond simulants like cubic zirconia. These changes follow numerous examples of sellers listing synthetic diamonds that were actually cubic zirconias or other imitations—a violation of the Federal Trade Commission’s Guides for the Jewelry Industry.

Under the new rules:

• The word diamond can be used only to describe a “natural mineral consisting essentially of pure carbon, crystallized in the isometric system,” the company says.

• Synthetic diamonds have to bear qualifiers like synthetic, man-made, lab-grown, or (name of company)-created.

• Cubic zirconia stones can use the word diamond only if the word is immediately preceded or followed by the words simulated or imitation, spelled out in full. The same goes for all other diamond imitations. Sellers also must provide details of the item’s composition in the item description.

“As a matter of law, [these requirements] have always been the case, and we have brought this to eBay’s attention many times,” says Cecilia Gardner, executive director of Jewelers Vigilance Committee. Gardner notes that her group is producing a booklet to help consumers distinguish between synthetic diamonds and nondiamond simulants.