# Stonehenge Altar Stone matches no examined UK Old Red Sandstone outcrop, geological study finds

- Published: 2026-11-12 07:17 UTC
- Section: Planet › Earth sciences
- Tags: Stonehenge Altar Stone, Altar Stone provenance, Old Red Sandstone, Orcadian Basin, detrital zircon, heavy mineral assemblage, Journal of the Geological Society, Neolithic monument
- URL: https://realtech.media/news/rt-3730051a11a2c70dd1822030_stonehenge_altar_stone/

**A multi-proxy study of the Altar Stone found that many Orcadian Basin outcrops could not be its source, so the stone's exact origin remains unknown.**

![Stonehenge Altar Stone matches no examined UK Old Red Sandstone outcrop, geological study finds](https://realtech.media/media/2026/11/4f203577cc481171.jpg)
*dailygalaxy.com*

A team led by Duncan Pirrie, emeritus professor at the University of South Wales, has published a detailed characterization of the Stonehenge Altar Stone in the Journal of the Geological Society. The six-tonne sandstone slab, about 4.9 m (16 ft) long, lies at the centre of the monument on Salisbury Plain. According to the authors, no examined outcrop area of the UK Old Red Sandstone (ORS) has the same suite of lithological and geochemical characteristics as the Altar Stone, so its exact provenance is still unknown. [1]

Stonehenge was built in several phases between around 3000 and 1600 BC. Many of its bluestones were transported about 225 km (140 miles) from West Wales. The Altar Stone differs in composition: it is a well-sorted, fine- to very fine-grained, calcite-cemented sandstone. Its purpose at the monument, and the time when it was brought to the site, are unknown. [1]

## Earlier proposals for the source

For about a century the prevailing view was that the Altar Stone came from West Wales. That interpretation was later discounted on geochemical and mineralogical data. More recently, the ages of detrital zircon, rutile and apatite grains in the stone were used to infer an origin in the Orcadian Basin of northeast Scotland. Richard Bevins, honorary professor at Aberystwyth University, said the earlier work overturned the West Wales assumption and pointed to Scotland as the most likely source. [1]

## What the new analysis showed

Direct sampling of the stone is not possible. The team therefore combined in situ analysis with the study of museum samples confidently attributed to the Altar Stone. They characterized its sedimentology, geochemistry, and detrital and diagenetic mineralogy, including clay mineralogy and the heavy mineral assemblage. [1]

The authors report that the earlier grain dating still supports a Laurentian source for the heavy minerals. However, the overall petrology, heavy mineral assemblage, clay mineralogy and geochemistry show that many ORS outcrops in the Orcadian Basin could not have been the source. [1]

Pirrie said none of the locations examined share the stone's full set of characteristics, so the search continues. Bevins said the study defines the specific geological characteristics to look for, which allows future work to be targeted. Nick Pearce, emeritus professor of geochemistry at Aberystwyth University, noted that each eliminated area narrows the search. [1]

## Sources

1. [Journal of the Geological Society](https://doi.org/10.1144/jgs2026-090)
2. [dailygalaxy.com](https://dailygalaxy.com/2026/11/altar-stone-origin-wrong-for-over-century)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-3730051a11a2c70dd1822030_stonehenge_altar_stone/