A worker at an Oregon construction site discovered a 2,000-pound rare rock believed to have arrived in the state on a glacier 15,000 years ago.
Jacob Parker said he was working at the site of the new Lakeridge Middle School in Lake Oswego when an unusual rock excavated by the crew caught his eye.
Parker used a rock identifying app that warned him the find might be radioactive, so he called in Scott Burns, a geologist from Portland State University.
Burns said the stone wasn’t radioactive, but is an extremely rare rock known as rhyolite.
Rhyolite is created by layers of cooling lava close to the Earth’s surface. Only one other piece of rhyolite has been discovered in Oregon previously.
“Basically, this is just a very, very rare rock,” Burns told KATU-TV.
The Tualatin Heritage Center, which took the rock for display as part of its Ice Age flood exhibit, said the rock likely formed in Montana or Canada and came to Oregon as part of a glacier during the Missoula Flood about 15,000 years ago.
“We believe it’s an ice-rafted glacial erratic,” Burns said in a release on the Tualatin Heritage Center’s website.
“That is, it fell onto the glaciers up in British Columbia, Alberta, Canada or Montana and then was part of the dam that blew apart in the Missoula Floods and it floated down here and was then dropped.”