A potential prehistoric artifact that looked like a humanly carved giant black rock was found in the frontyard of an Edmonton couple. Archaeologists who studied the mysterious object found that it was a 4.6-pound chunk of obsidian core. might be living on a piece of history. The only other such stone in Alberta is on display at the Royal Museum.

Through the use of X-ray spectrometry, the chemical on the rock has been matched to a volcano in southern Idaho. The rock could be the tip of a historical mystery about whether Alberta was a tool making center for the indigenous people, a claim that has never been proved before. However, the critical question remains how the artifact reached the backyard of Jennifer Yeoman.

While doing some landscaping of their yard last year, Yeoman and her husband Hector Lomack found the curious-looking object. The Edmonton couple later discovered that they got their hands on a potential prehistoric artifact. Notably, because there aren’t many volcanoes in Alberta, obsidian core—a form of volcanic glass—don’t typically occur there.

“As Hector was digging out the front, I was out here around and about, and he came to me with a big black rock, and he said: ‘What’s this?’.. It’s the oddest piece of rock I’ve ever seen in my life. It’s a sheer big piece of glass,” Global News quoted Yeoman as saying.

Following a potential discovery, archeologists have been tasked with investigating and further taking the mystery behind the blank rock to its historical inception.

“It turned out there’s only one other rock found that size in Alberta to date, and it happened to be our rock,” Yeoman told the outlet. As lava cools quickly with little crystal formation, it forms the obsidian core, which is supposedly volcanic glass that is the material used to form the mysterious black artifact.