Scientists have ruled out Scotland’s Orcadian Basin as the source of Stonehenge’s six-tonne Altar Stone, narrowing the search for its birthplace without establishing where it came from.

Tests in the area failed to find rock matching the characteristics of the 4.9-metre sandstone slab. The finding eliminates a proposed source area, rather than overturning the broader suggestion that the stone originated in north-east Scotland.

The Altar Stone, which lies within the circle and is now mostly buried, was initially thought to have come from Wales. More recent research pointed instead towards north-east Scotland, prompting further investigation of its geological origins.

Published in the Journal of the Geological Society, the latest study combined new observations with an examination of fragments held in museum collections. Researchers analysed the stone’s structure, minerals and composition to refine the evidence against which possible source locations can be tested.

Professor Duncan Pirrie, of the University of South Wales, who led the study, described it as “the most comprehensive geological investigation of the Altar Stone ever undertaken”. He said the team was now “far better equipped to focus on the areas most likely to yield an answer.”

Professor Nick Pearce, a geochemistry expert at Aberystwyth University who worked on the earlier research, said “ruling out potential source areas is just as important as identifying new ones”.

Stonehenge was constructed in several phases between 3000 and 1600 BC, and its stones were not all obtained locally. The smaller bluestones travelled about 225km from west Wales; research suggests a few were taken directly from another stone circle.

The Altar Stone is unique among the monument’s stones. Identifying its source would provide a firmer starting point for understanding its journey to Salisbury Plain thousands of years ago. For now, the research has established where the search should no longer concentrate, rather than where that journey began.