Geologists have ruled out north-east Scotland as the source of Stonehenge’s six-tonne Altar Stone, according to a study published in the Journal of the Geological Society.
Archaeologists have debated the origins of the monolith at the heart of the Wiltshire monument for more than a century, initially believing it came from Wales.
The monument was constructed in several phases between 3000 and 1600 BC. An international team of scientists from the UK, Canada, Italy, and Sweden combined detailed analysis of the sandstone with rock tests in the Orcadian Basin, some 435 miles away from Stonehenge. However, the researchers failed to find a location in the region with the same chemical and mineral characteristics as the monument’s central slab.
Scientists worked from eight museum fragments confidently linked to the Altar Stone, alongside portable X-ray measurements of exposed patches at the site. The stone contains a distinctive scatter of baryte and chrome spinel, minerals that distinguish it from Old Red Sandstone across much of the Orcadian Basin.
Emeritus professor Duncan Pirrie of the University of South Wales, who led the study, stated that none of the locations examined matched the stone’s composition.
“This is the most comprehensive geological investigation of the Altar Stone ever undertaken,” Professor Pirrie said. He added that the search is not over, but that researchers are now better equipped to focus on more likely areas.
For decades, researchers assumed the Altar Stone originated in west Wales alongside the monument’s smaller bluestones, which traveled approximately 225 kilometres to Salisbury Plain. A 2024 study challenged that view by pointing to Scotland, sparking new debates about whether Neolithic people transported the heavy slab by sea or sledge. Honorary professor Richard Bevins of Aberystwyth University noted that the latest work refines the geological characteristics required for future investigations.
“In a geological detective story such as this, ruling out potential source areas is just as important as identifying new ones,” said Professor Nick Pearce, professor of geochemistry at Aberystwyth University. Every location eliminated narrows the search for the stone’s origin.
Research indicates the smaller bluestones travelled roughly 225 kilometres from west Wales to Wiltshire during the construction phases between 3000 and 1600 BC.
Because the Altar Stone itself cannot be sampled directly, researchers relied on eight museum fragments linked to the slab and portable X-ray measurements of exposed patches at the site.
With southern Britain, the Midland Valley of Scotland, and the Orcadian Basin excluded, researchers suggest the stone may have originated from elsewhere in Scotland, northern England, or Ireland.
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