The plot has thickened on the mystery of the altar stone of Stonehenge, weeks after geologists sensationally revealed that the huge neolithic rock had been transported hundreds of miles to Wiltshire from the very north of Scotland. That discovery, described as “jaw-dropping” by one of the scientists involved, established definitively that the six-tonne megalith had not been brought from Wales, as had long been believed, but came from sandstone deposits in an area encompassing the isles of Orkney and Shetland and a coastal strip on the north-east Scottish mainland. Many experts assumed that the most likely place of origin was Orkney, based on the islands’ rich neolithic culture and tradition of monument building. But a separate academic study has now found that Orkney is not, in fact, the source of the altar stone, meaning the tantalising hunt for its place of origin goes on. The new study, which was conducted separately from last month’s Australian-led paper but involved some of the same scientists, examined the chemical and mineralogical makeup of the stones in Orkney’s two great stone circles – the Stones of Stenness and the Ring of Brodgar – as well as field samples of rock deposits across Orkney’s islands. When their key markers, identified in portable X-rays, were compared with those of the altar stone they were found to be strikingly different, leading the authors to conclude that Orkney could not be its source. The report’s lead author, Richard Bevins, an honorary professor of geography and earth sciences at Aberystwyth University, said Orkney had seemed “the obvious place to look” once initial research some years ago had pointed away from Wales to an unknown location in northern Britain. Extensive evidence exists of long-distance communication between Orkney and Stonehenge around 3000BC, and a number of key innovations in technology and culture are believed to have originated in the archipelago. “Everybody and their dog would have said: ‘Let’s try Orkney first. It’s going to be Orkney,’” agreed co-author Dr Rob Ixer, an honorary senior research fellow at University College London, who, like Bevins, was involved in the Australian-led research. He added: “Life would have been far simpler had it turned out to be similar to the stones of Brodgar. “The more we learn [about Stonehenge], the weirder it gets.” Ruling out Orkney so quickly could help narrow the search in other areas of old red sandstone, said Bevins, adding that he was “optimistic” the specific source of the boulder would be identified one day. “The Orcadian basin [the area of old red sandstone from which the altar stone originated] is quite a big area, so I wouldn’t say it will be found quickly. What I would say it is, it is achievable.” Ixer said he would be “astonished if there weren’t other people shoving little probes around suitable stones” in Aberdeenshire and Caithness. Alison Sheridan, the former principal curator of prehistory at National Museums Scotland (NMS), who was not involved in the research, said the new findings were “an intriguing additional twist to the tale”. She added: “As with many things from Stonehenge, nothing is ever straightforward.” Attention had understandably turned to Orkney because of what was known of the sophisticated society that built the Ness of Brodgar, said Sheridan, who is now a research associate at NMS. “What we don’t know as much about is the social organisation of other parts of Britain at the time. There’s clearly scope that people were just as sophisticated and well connected geographically and socially [elsewhere]. “I think it would do no harm for us to reconsider what we already know about late neolithic communities in north-east Scotland.” The study is published in Journal of Archaeological Science.