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Follow the Money: Geologist Links Pennies to Historic Copper Deposits

(Posted October 13, 2008)

Ryan Mathur, associate professor of geology offers a couple of thoughts as he teaches the Mining in the Americas course

HUNTINGDON, Pa. -- Ryan Mathur has a lot of thoughts about pennies. More specifically, the associate professor of geology at Juniata College thought it would be interesting to see if he could trace the copper used in U.S. pennies to the mine that produced the metal.

"Copper has two isotopes that give off distinct signatures depending the ratio of each isotope in the ore deposit it was taken from," explains Mathur, a coin collector and a geologist specializing in copper ore deposit research. "I was wondering if you could trace back a copper product to the mine it was taken from and I just happened to have a penny in my pocket."

Mathur tested the penny, then tested other pennies and discovered that the copper in many of the pennies minted in the 19th and early 20th century came from single sources and that an analysis of the copper would yield a very specific signature of copper isotope ratios.

Intrigued by his results, Mathur, who studied history during his undergraduate career at Juniata (he is a 1998 graduate), decided to trace the copper in historic pennies to see if he could match the penny to the copper deposits where the copper originated.

The science was simple. He admits that he broke the law by cutting apart a few cents in the name of science. He cut a sample, dissolved a portion of the penny in acid, suspended the copper in solution and used a mass spectrometer to gain a unique signature for the metal.

"I tell people I spent $500 and 50 cents on the project."
Ryan Mathur, associate professor of geology

But, before he could put in his two cents on how to trace pennies, the geologist had to research how copper was used in pennies. He found that from 1810 to 1981 95 percent pure copper was used to mint pennies. By e-mailing what he termed "5 million people," Mathur discovered that the copper used to mint pennies from 1810 to 1835 came from the same mine in Cornwall, England.

In order to link the copper in an 1810 penny, Mathur had to find one, which turned out to be easy. He bought one for $150 at a Huntingdon coin dealer. Next he had to find a sample of copper taken from the Cornwall mine. That turned out to be pretty simple as well.

It seems that Pittsburgh's Carnegie Museum of Natural History holds samples of ore deposits from all over the world. Mathur has worked with curator Marc Wilson, director of the Hillman Hall of Minerals, to classify rock samples and Wilson agreed to provide copper samples. Sure enough, the sample from the 1810 penny matched the museum's ore sample from Cornwall.

At the same time, Mathur delved into historical records to find out whether the copper used for coins in the United States came from traceable sources. He discovered that the United States bought copper from a variety of sources from 1835 to 1844. However, starting in 1845, most of the copper used in the United States came from a huge deposit known as the Keneewa Peninsula copper deposits in Michigan.

"It not only supplied the copper for pennies but it also supplied the copper for railroad tracks and telegraph wires that allowed people to move west," Mathur says. "The reliance on a single mine lasted until 1872 when we began using copper purchased from all over the world."

Mathur found original correspondence in the archives of the U.S Mint in Philadelphia from the Director of the Mint that detailed a new policy of buying copper from multiple international sources to protect the United States' domestic resources.

"Later, when we made much larger copper discoveries in Montana and Arizona, we went back to using domestic copper for about 60 to 70 percent of our pennies," Mathur explains.

Mathur also was able to trace later pennies, minted in Denver, made from copper from the massive Anaconda mine in Butte, Mont. and to other mine deposits. In all cases he was able to match the pennies to mine ore deposit samples from the Carnegie Museum of Natural History collection.

Although Mathur used pennies as his guide into the past, he points out that using distinct identifying signatures from specific ore deposits can also be applied to any object made from or containing copper that came from those sites. "For example, a Native American artifact made from copper could be traced back to the Michigan basin mine or other American mines," he explains. "If a copper artifact is found in Pennsylvania and the copper originated in Michigan or Montana, then that's an identifiable link that trade existed between those sites."

In the course of his research, Mathur followed the penny trail to the Archives of the U.S. Mint in Philadelphia, the University of Arizona to use its mass spectrometer, the Carnegie Museum and the University of Maryland. Fueled by his own curiosity, Mathur financed the project himself, paying for lab time and buying a couple of older coins. "I tell people I spent $500 and 50 cents on the project," he laughs.

He also says researchers interested in similar research can avoid dissolving the coins by analyzing copper using laser ablation, The laser is pointed at the sample and removes a micron-sized sample of the material and beams it into a mass spectrometer. The method does not destroy the ore sample or artifact, although the laboratory time is much more expensive. "The Ryan Mathur Fund only goes so far," he says.

Having satisfied his curiosity about pennies, Mathur has moved onto other research, but he will be publishing an article near the end of the year about the experiment in the Journal of Archeological Science.

Contact John Wall at wallj@juniata.edu or (814) 641-3132 for more information.