Two high school students found a 6,000-year-old Native American stone ax on George Washington’s estate in Virginia. 

Ohio seniors Dominic Anderson and Jared Phillips made the sensational discovery while on an archaeological dig at Mount Vernon, as they mapped a plot of land believed to be a cemetery for slaves, reports the Washington Post.

Mount Vernon officials said the ax had been fashioned out of “green stone,” probably sourced from a local river. Skilled craftsmen would’ve shaped the tool by chipping away at it to create a smooth cutting edge with a harder, heavier grinding stone. The back of the ax-head includes a groove for a wooden handle so that it could be used for chopping down trees. It was probably highly valuable, officials said.

Measuring 7 inches (17.8 cm) the discovery of the ancient tool gives important insight into the way of life of the indigenous population that settled on the land before the arrival of European colonists.

“The ax provides a window onto the lives of individuals who lived here nearly 6,000 years ago,” Mount Vernon’s archeological curator Sean Devlin said while announcing the discovery last Wednesday. “Artifacts such as this are a vital resource for helping us learn about the diverse communities who shaped this landscape throughout its long history.”

George Washington’s Mount Vernon estate. Photo: DANIEL SLIM/AFP/Getty Images.

The ax was found at Mount Vernon’s African American cemetery, which is believed to be the resting place for slaves and possibly their freed descendants. Prior to the Washington family’s occupation of the estate in 1674, experts believe the site was used as a temporary stopping place for nomadic indigenous tribes as they traveled along the Potomac River on the border of Virginia and Maryland between 6,000 and 8,000 years ago. 

The historic artifact is now part of the Mount Vernon archaeology collection.

Mount Vernon was first occupied by George Washington’s great-grandfather in the second half of the 17th century. The first president of the United States moved in after inheriting the estate from his half-brother Lawrence in 1754. Washington lived on the estate until his death in 1799—with the exception of his tenure as president, which he spent in New York from 1789 to 1790 and in Philadelphia from 1790 to 1797.

Mount Vernon itself was added to the National Register of Historic Places by the US National Park Service in 1960.