DURHAM, N.C. — Durham police investigators are issuing a warning about a scam involving diamond rings sold through newspaper classifieds.

A man called police on Wednesday to report that he had responded to a newspaper ad about a diamond ring earlier this month. He said he called the telephone number listed in the ad and spoke to a woman who said she would meet him in Durham on Tuesday to complete the sale.

The man told the investigators he paid the woman several thousand dollars for the ring, which was listed as a four-carat diamond. The woman told him the ring had been appraised but did not provide him with any documentation.

When the man later took the ring to a jeweler, he learned that the ring contained diamond fill and was not worth nearly what he paid for it.

Diamond fill, which is usually leaded glass, is a clarity-enhancer used to fill in cracks in a diamond.

The buyer told investigators he knew only the woman's first name and her cell phone number. He did not know where she lives or who she is.

Investigators described the suspect as a white female in her late 50s or early 60s who was driving a white Cadillac Escalade.

Investigators said buyers should get an appraisal before paying for expensive jewelry and get a contract that contains information about the seller.