The United States has never been a major diamond producer, but it has a few real diamond deposits and a long record of chance finds. The best known is Crater of Diamonds State Park in Murfreesboro, Arkansas, where anyone who pays the entry fee can search for diamonds and keep what they find. Kimberlites along the Colorado and Wyoming border supported a short-lived commercial mine at Kelsey Lake in the 1990s.
Crater of Diamonds State Park
The Arkansas deposit lies in Pike County in the southwest of the state, near the town of Murfreesboro. Geologists describe it as the eroded surface of a volcanic pipe formed roughly 100 million years ago. The rock was long classed as lamproite, the same family as Australia's Argyle host rock, and some later studies have described it as closer to kimberlite. Either way, it carried diamonds up from the mantle. The page on diamond geology explains how these pipes form.
Discovery and early mining
In 1906 a farmer named John Wesley Huddleston found two crystals on his land and had them identified as diamonds. The news set off a local rush, and the town of Murfreesboro filled with prospectors and speculators. Several companies tried to mine the deposit commercially over the following decades. None turned a lasting profit. Low ore grades, disputes between owners, legal fights and fires at processing plants were blamed at different times.
A state park
The site was run as a private tourist attraction from the 1950s, and visitors paid to search for stones. The State of Arkansas bought the land and opened it as Crater of Diamonds State Park in 1972. The park keeps a plowed search field of about 37 acres, which staff turn over periodically to bring fresh ground to the surface. Visitors can dig, sift and wash soil, and the park's rule is simple: finders keep what they find.
Thousands of diamonds have been recorded at the park since 1972, most of them small. The park staff identify finds for visitors at no charge. Arkansas diamonds tend to be white, brown or yellow, and many show smooth, rounded crystal faces from natural resorption in the magma. They are often left uncut and set in jewelry as found; see rough diamond jewelry.
Famous Arkansas diamonds
The largest diamond found in the United States came from the Arkansas deposit. The Uncle Sam, found in 1924 during commercial mining, weighed about 40.23 carats as rough. It was cut into an emerald-cut stone of about 12.42 carats.
Other well-known stones include:
- The Strawn-Wagner Diamond, found in 1990 as a 3.03-carat rough and later recut. It received one of the highest possible grades from the American Gem Society, a top color and clarity grade with an ideal cut. The AGS diamond grading report page explains AGS grading.
- The Kahn Canary, a yellow stone of about 4.25 carats found in 1977 and kept uncut.
- The Esperanza, found by a visitor in 2015 at about 8.52 carats, later cut into a modified triangular shape.
Kelsey Lake and the State Line district
A cluster of kimberlite pipes straddles the border between northern Colorado and southern Wyoming, known as the State Line district. Geologists from the U.S. Geological Survey identified kimberlites there in the 1960s and 1970s, and drilling and sampling showed that some contained diamonds.
The Kelsey Lake mine, on the Colorado side, operated in the mid-1990s. It was the first commercial diamond mine in the United States in decades. It produced some gem-quality stones, including a diamond of about 28.3 carats, among the largest found in North America at the time. The mine closed after a few years, with low grades and financing problems cited as reasons. The site was later reclaimed. The how diamonds are mined page covers the open-pit methods used at operations like Kelsey Lake.
Glacial and placer finds
Diamonds have also turned up far from any known source. Glaciers carried stones south from Canada during the ice ages and dropped them in glacial drift across the Great Lakes region. Diamonds have been found in Wisconsin, Michigan, Ohio, Indiana and Illinois this way. The Eagle Diamond, a stone of roughly 16 carats found in Wisconsin in 1876, is one of the best known. It was stolen from the American Museum of Natural History in New York in 1964 and never recovered.
Gold miners in California's Sierra Nevada and in the Appalachians of Georgia, North Carolina and Virginia found occasional diamonds in placer gravels in the 19th century. One of the larger Appalachian finds was the Dewey Diamond, about 23.75 carats, found in Virginia in 1855.
Why the United States has few diamond mines
Large diamond deposits need old cratons with deep, cool roots where diamonds can form, and then kimberlite or lamproite eruptions that bring them up. Parts of the United States sit on old crust, but no American pipe has proven rich enough to support a large mine. The country's diamond story is mostly about public digging, collector stones and history. For how the U.S. compares with countries that hold big pipes, see the page on diamond mines of the world and diamond mines of Canada.
Frequently asked questions
Can you dig for diamonds in the United States?
Yes. Crater of Diamonds State Park near Murfreesboro, Arkansas, lets visitors search for diamonds for a fee and keep what they find.
What is the largest diamond found in the United States?
The Uncle Sam, found in 1924 at the Arkansas deposit, weighed about 40.23 carats as rough. It was cut into a stone of about 12.42 carats.
Was there ever a commercial diamond mine in the United States?
Yes. Commercial attempts were made in Arkansas in the early 20th century, and the Kelsey Lake mine in Colorado operated in the 1990s. None lasted long.
Why do diamonds turn up in the Great Lakes states?
Glaciers carried diamonds south from sources in Canada during the ice ages and dropped them in glacial deposits. Their exact source pipes have not been identified.