A California jeweler was arrested on suspicion of passing off approximately $240,000 worth cubic zirconium stones as real diamonds to nearly two dozen customers over a five-year period, according to San Jose police and media reports.

Gerald Dan Mokma, 60, of Santa Clara, was arrested Sept. 18 on a warrant for grand theft, according to a statement by the San Jose Police Department. 

Twenty victims have been identified, police told the San Jose Mercury News. In addition, according to a San Jose Police statement, police are urging people who may have bought fake diamonds at Mokma’s Willow Estates Jewelry of San Jose to have their gems appraised then contact fraud investigators.

Police said in its statement that it began investigating the jeweler in February after a local television news station aired a story about customers of Willow Estates Jewelry who were defrauded by Mokma, discovering they purchased synthetic diamonds instead of a genuine diamond.

Police said none of the customers interviewed by the news station had filed a police report of the alleged misrepresentations. Detectives served search warrants at Mokma’s residence where evidence obtained indicated additional victims.

The Mercury News also reports that an alleged robbery at the store turned out to be faked, according to Santa Clara County Superior Court documents.

Police told the newspaper that Mokma has been selling the phony gems for more than five years, although nobody had filed a police report.

JCK