"X-ray technology has allowed researchers a glimpse at the reaches of the Yellowstone landmark’s prized stone and its importance to Indigenous people."
"YELLOWSTONE NATIONAL PARK, Wyo. — Near the north entrance, an imposing mountain of black glass rises against the blue sky.
Spanning more than five square miles, the dark, sometimes translucent mass was formed from a rhyolitic lava flow that oozed out of the magma chamber of Yellowstone Caldera beneath the park, and cooled rapidly in the bitter cold of a glacial maximum, about 180,000 years ago.
Known as Obsidian Cliff, the Yellowstone mountain is one of the country’s highest quality deposits of “the sharpest natural substance on Earth,” according to Douglas H. MacDonald, a professor of anthropology at the University of Montana and the author of “Before Yellowstone: Native American Archaeology in the National Park.”"