New Research

Mysterious Green Rocks Discovered in a Remote Cave in Spain Might Be Signs of Prehistoric People Working With Copper

The find challenges assumptions that people in the region thousands of years ago did not spend much time at high altitudes

Mary Randolph | Correspondent

May 8, 2026 1:42 p.m.

Share

Copy linkEmailSMSFacebookXRedditLinkedInBlueskyPrint

Add as preferred source

To get to Cave 338, high in the Pyrenees mountains, you must go primarily by foot. That’s exactly what a team of archaeologists did during a recent excavation—and likely exactly what people did thousands of years ago, when the area may have served as a copper processing site.

A new study published this week in Frontiers in Environmental Archaeology found hearths, jewelry, children’s bones and a green mineral that researchers think is malachite, a mineral that is a source for copper.

Previously, archaeologists thought that prehistoric peoples in that region rarely spent time at high altitudes. But this new discovery proves otherwise.

“Cova 338 forces us to rethink the role of high mountain environments in Pyrenean prehistoric societies,” says Carlos Tornero, the study’s lead author and a researcher at the Catalan Institute of Human Palaeoecology and Social Evolution, in a university statement. “For a long time, these spaces were assumed to be marginal. What we document here is recurrent occupation, with complex activities and a clear exploitation of mineral resources.”

Between the Stone Age and the Bronze Age came a transitional period when humans started working with copper. The element was useful because it is easy to shape, resists corrosion and conducts heat well. By the middle of the fourth millennium B.C.E., Mesopotamians were working with copper to create tools and weapons. And by 3,000 B.C.E., Neolithic cultures in Europe were starting to use copper. Along the way, people realized that when copper is alloyed with tin, it produces bronze.

The archaeologists found four different layers in the cave in Spain that reflect periods of human visits. The earliest layers contained just charcoal and the latest were very thin, but the two middle layers, dating from 5,500 to 3,000 years ago, held several hearths containing burned fragments of what might be malachite.

Malachite is not found naturally in the cave, so the archaeologists think prehistoric people might have hauled it up the mountain to process it, reports Kristina Killgrove in Live Science.

“Many of these fragments are thermally altered, while other materials in the cave are not, which clearly suggests that fire played an important role in their processing and that there was a deliberate intention behind it,” Julia Montes-Landa, study co-author and an archaeologist at the University of Granada in Spain, says in a statement from Frontiers. “In other words, they weren’t burned by accident.”

There’s several reasons prehistoric people may have traveled so high to produce copper, ZME Science’s Mihai Andrei reports. It’s possible the cave was more sheltered because it was so high, or that mineral extraction sites were easily accessible, though the team has not yet found a mining site close by.

From the dating of the objects found, it seems as though the cave was not a permanent settlement but that prehistoric peoples visited often for short periods of time between the fifth millennium B.C.E. and the end of the first millennium B.C.E. The presence of children’s bones also suggests the cave could have served as a burial or ritual site

“This site demonstrates that the Pyrenees were not a marginal territory for prehistoric communities, but a space fully integrated into their mobility strategies and territorial exploitation,” Tornero says in the university statement.

Archaeologists will continue to make the journey to Cave 338 and are currently working to confirm the identity of the green mineral.

Mary Randolph | Read More

Mary Randolph is a former editorial intern with Smithsonian magazine.