(CNN) - Don Lutes Jr. kept the 1943 copper penny he stumbled upon in his high school cafeteria seven decades ago in a safe behind a wall in his Massachusetts home.
All US pennies were supposed to be made of zinc-coated steel that year to conserve the copper needed for wartime essentials like shell casings and telephone wire, according to Heritage Auctions, a Dallas-based auction house. But a small number of copper pennies were created by mistake. Only a few of them exist today, making them special to coin collectors.
Lutes knew his coin was rare and held on to it. But as his health declined last year, Lutes decided to sell the coin, said Peter Karpenski, a friend and fellow coin collector.
Lutes' prized possession could fetch a pretty penny. Heritage Auctions, which is overseeing the sale, estimates the coin is worth at least $170,000.
The top bid after a two-week online auction is $130,000, according to Heritage Auctions. The online auction ends at 6 p.m. Thursday when a live auction will begin at the Florida United Numismatics convention in Orlando.
"What makes this so exciting is that it's the only time ever in history when the discovery coin for this piece has been available for sale. In other words, this was the first one that was ever found," said Sarah Miller, Director of Numismatics for Heritage Auctions' New York office.
The 1943 copper penny "is the most famous error coin," according to Heritage Auctions.
Around the end of 1942, a small number of bronze planchets -- a plain metal disk that is stamped as a coin -- got caught in the trap doors of the mobile tote bins used to feed the blanks into the Mint's coin presses, according to Heritage Auctions. Those planchets went unnoticed when the bins were refilled with zinc-coated steel planchets in 1943, Heritage Auctions said.
"They eventually became dislodged and were fed into the coin press, along with the wartime steel blanks. The few resulting copper cents were lost in the flood of millions of steel cents struck in 1943 and escaped detection by the Mint's quality control measures," according to Heritage Auctions.
Miller said 10 to 15 of the 1943 copper pennies exist today.
Lutes set his 1943 copper penny aside to study it later when he found it in a bundle of change in the Pittsfield High School cafeteria in 1947.
A US Army veteran, he would amass some 50,000 coins by the 1970s when he retired from the family manufacturing business, according to Karpenski. Lutes died in September 2018 at the age of 87, according to Miller.
The Pittsfield resident was a quiet man with a small circle of friends that included fellow members of the coin and genealogy clubs he belonged to. A widower, he volunteered for decades at Berkshire Athenaeum, Pittsfield's public library, according to Karpenski, who owns a coin store in Pittsfield.
The library named a volunteer of the year award after him, according to Karpenski.
And the library meant just as much to Lutes.
Lutes wanted the proceeds from the sale of his prized penny to go to the library, Miller said.
The-CNN-Wire ™ & © 2019 Cable News Network, Inc., a Time Warner Company. All rights reserved.