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The Altar Stone lies flat on the ground, sunk into the lawn below the collapsed upright of the Great Trilithon and its lintel. Image credit: Nick Pearce, Aberystwyth University.
The Altar Stone, an approximately 4.9-m piece weighing an approximated 6 heaps, lies primarily buried below 2 fallen sarsen stones at the center of the monolith.
For years it was believed to have actually originated from West Wales, like the majority of the smaller sized bluestones. In 2020, geologists revealed this was incorrect.
In 2024, a group led by Curtin University scientist Anthony Clarke, utilizing the ages of small mineral grains in pieces of the stone, concluded it originated from the Orcadian Basin of northeastern Scotland, a journey of some 700 km or more.
According to Professor Pirrie and co-authors, the photo is far less settled.
They do not challenge the earlier dating work, which indicates a Laurentian origin, indicating ancient crust connected with the Scottish Highlands, for the heavy minerals in the stone. Age information alone, they argue, are not enough.
“This is the most detailed geological examination of the Altar Stone ever carried out,” Professor Pirrie stated.
“By integrating a large range of analytical strategies, we have actually constructed the clearest photo yet of the stone’s structure and evaluated the leading theories about its origins.”
“So far, none of the places taken a look at have the very same set of qualities as the Altar Stone.”
“That informs us the search is not over, however we are now far much better geared up to concentrate on the locations probably to yield a response.”
Due To The Fact That the Altar Stone itself can not be tested, the scientists worked from 8 museum pieces with confidence connected to it, in addition to portable X-ray measurements of the 3 little spots of the stone that are exposed at Stonehenge.
The stone includes an unique scatter of baryte, a barium mineral that seals the sandstone’s grains, which offers the stone uncommonly high barium readings.
It likewise holds chrome spinel, a heavy mineral that is limited in Old Red Sandstone from much of the Orcadian Basin, consisting of Orkney, Caithness, the Moray Firth and Shetland.
The stone’s mixed-layer illite/smectite clay has about 20% expandable layers, an indication it has actually not been deeply buried or heated up. Rocks in Caithness and Orkney reveal worths listed below 10%, which would omit those locations.
The stone likewise consists of tosudite, an uncommon clay mineral, and reveals no indication of the low-grade metamorphism discovered in the Southern Uplands of Scotland, which rules the area out.
The stone’s ripple-laminated structure follows deposition by streaming water, which its calcite cement formed throughout burial instead of near the surface area.
Other prospects, West Wales and the broader Anglo-Welsh Basin, were omitted previously.
The Midland Valley of Scotland is eliminated by its abundance of rock pieces.
Carboniferous sandstones from southern and main Britain are a poorer isotopic match than the Old Red Sandstone, although the Old Red Sandstone’s isotope record is insufficient since strontium information are missing out on.
“For practically a century, the dominating view was that the Altar Stone originated from west Wales,” stated Aberystwyth University’s Professor Richard Bevins.
“Our previous research study reversed that presumption and pointed rather to Scotland as the most likely source.”
“This newest research study substantially fine-tunes the search by determining the particular geological attributes we require to search for, enabling future examinations to be targeted better.”
“With each brand-new piece of proof, we move more detailed to fixing among Stonehenge’s most long-lasting secrets.”
“In a geological investigator story such as this, dismissing prospective source locations is simply as crucial as determining brand-new ones,” included Professor Nick Pearce, likewise from Aberystwyth University.
“Every place got rid of narrows the search and brings us closer to finding where the Altar Stone came from.”
“The stone is special amongst those at Stonehenge, and tracing its source would offer important brand-new insights into its exceptional journey to Salisbury Plain countless years earlier.”
The research study was released today in the Journal of the Geological Society
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Duncan Pirrie et al2026. Searching for the origin of the Stonehenge Altar Stone: brand-new sedimentological, petrographical, mineralogical, geochemical and isotopic restrictions. Journal of the Geological Society 183; doi: 10.1144/ jgs2026-090
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