An experimental penny made of glass during World War II is about to be auctioned.

Owner Roger Burdette says the coin is the only known unbroken glass penny in existence.

During the war, copper was needed for ammunition. The U.S. Mint authorized tests that included making uncirculated pennies from other metals, plastic and rubber. The Blue Ridge Glass Co. in Tennessee made experimental pennies using tempered glass.

Burdette says the impressions on the coins weren't precise, the weight and size weren't uniform and the coins developed sharp edges that cut fingers. He says they were likely destroyed. He says only one other glass penny exists, and it is broken.

The Mint made 1943 pennies from low-grade steel covered in zinc.

Heritage Auctions in Fort Lauderdale is conducting Thursday's bidding.

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This story has been corrected to show the penny will be auctioned Thursday, not Wednesday.