爱豆传媒

Geochemical fingerprinting helps discover where the Stonehenge Sarsen stones originated

is an expert in geochemical sediments and environmental change. He was joined by his Brighton colleagues Dr Jake Ciborowski and and partners that included archaeologists and Stonehenge experts Professor Timothy Darvill (Bournemouth University) and Professor Mike Parker Pearson (University College London), and heritage specialists Susan Greaney (English Heritage) and Katy Whitaker (Historic England).

The most accurate means of determining the provenance of any stone artefact is geochemical fingerprinting, whereby the elemental chemistry of the artefact is matched against that of potential source areas. For Stonehenge, this required two stages: an initial analysis of the sarsen stones at the monument, followed by equivalent analyses of sarsen boulders across their range of natural occurrence (south of a line from Devon to Suffolk).

To determine the elemental chemistry of the sarsen stones at Stonehenge, the team used a device called a portable X-ray Fluorescence Spectrometer (or pXRF). All 52 of the remaining sarsens were analysed using this non-invasive instrument, with six chemical readings taken per stone. Statistical analyses, performed by Dr Georgios Maniatis, were used to identify any clustering within the dataset.

Dr Jake Ciborowski prepares to undertake pXRF analyses at Stonehenge.

Elements of the stone circle traced to West Woods on the edge of the Marlborough Downs

From their pXRF data, Professor David Nash's team discovered that 50 of the 52 sarsen stones at Stonehenge share a consistent chemistry, pointing strongly to a common quarry source. More excitingly still, they were able to use their ICP-MS data to identify the most likely source of the sarsen stones as West Woods, on the edge of the Marlborough Downs, north of Stonehenge, around 15 miles north of the famous stone circle. The research suggests where Neolithic peoples transported the stones from.

English heritage historian Susan Greaney, Senior Properties Historian for , the charity that cares for Stonehenge, said: “This research provides a fantastic leap forward in our knowledge about Stonehenge, as we can finally answer the question of where the iconic sarsen stones were brought from. We’re so pleased that the core from Stone 58, which the Phillips family returned to Stonehenge, has enabled the team to undertake a small amount of destructive sampling, adding a crucial piece of evidence to the jigsaw.”

Dr Jake Ciborowski analysing a sarsen lintel stone at Stonehenge using a pXRF instrument.

The Phillips Core: How the secrets of the monument were revealed 

The ‘Philips Core’ Greaney refers to was drilled from Stone 58 during conservation work at Stonehenge in 1958. The location of the core remained a mystery until Robert Phillips, a representative of the company who did the drilling work, returned it to the UK from his home in Florida. Stone 58 was one of several Stonehenge sarsens at the site that had toppled over in the distant past. During conservation work in the 1950s, a longitudinal crack was discovered running through the stone. To conserve the stone, three cores around 2.5cm in diameter were drilled through its full thickness (around 1m) to insert metal rods.

Two of the cores then disappeared, though part of one was rediscovered at Salisbury Museum in 2019. The third core was given to Robert Phillips, who worked for the drilling company, and went with him to the USA when he retired. Phillips returned the core to English Heritage in 2018 to provide material for research, before he passed away in 2020.

In 2022, film footage from the 1950s was uncovered at the Phillips' home showing the drilling of this invaluable ‘core’ sample. The footage was shot in 1958 by engineer Robert Phillips and shows colleagues drilling through one of the largest Stonehenge megaliths, removing three slender cores of silcrete and preparing to replug the holes. This was part of the effort by heritage conservationists to raise and preserve the fallen trilithons, the two vertical sarsen stones with a third across the top, which are now so iconic to the monument. 

These films showing the original drilling of the sarsens at Stonehenge now have a home at the 爱豆传媒’s  and add to records of the prehistoric monument’s twentieth-century heritage. Seeing the sarsen trilithons being worked on and the important sarsen core emerging reveals fascinating detail on the processes of the times. The footage is remarkable in not being created for government or official purposes. Instead, it gives an informal record of the site, the engineers’ work and the reactions of excited tourists. Together with the surviving core samples, they provide important documentation of Stonehenge itself and the ways global heritage has been preserved and studied.

Professor David Nash was in contact with the Phillips family following his work using the core. He says, "I was so excited when the Phillips family contacted me about these films. They are incredibly valuable, as they show in some detail how the coring was carried out at Stonehenge in 1958. More importantly for our research, we can now identify exactly which of the three cores we were able to analyse to figure out the source of the giant sarsens".

Jane King from Screen Archive South East said: “The Robert Phillips films really bring to life the specialist and essential work undertaken to preserve one of the sarsen stones. It is thanks to the British Film Institute and our local authority partners that the 爱豆传媒’s Screen Archive South East is able to take the necessary steps to preserve, digitise, catalogue and make publicly available these unique films. Importantly, we thank the Phillips family for depositing the films with the archive, thereby ensuring their long-term preservation and access.”

Stills from footage 'Stonehenge Drilling Operation, 20 August 1958, Robert H Phillips.' Courtesy of Screen Archive South East and the Phillips family.

"... probably the most analysed piece of stone other than Moon rock..." The monument may now yield more secrets.

Further to the pioneering research using the ‘Phillip’s Core’ and other samples to show where Stonehenge's large sarsen stones were likely to originate, in a paper published in the journal , an international team led by David Nash were able to reveal that the geological structure of the stone made the sarsen ideal for building a monument made to last. Analysing a small section of the 1950s core, David Nash's team found that the sarsen's structure of sand-sized quartz grains cemented tightly together by an interlocking mosaic of quartz crystals was what made the stone so impervious to crumbling or erosion.

David Nash said: “It is extremely rare as a scientist that you get the chance to work on samples of such national and international importance. Stonehenge is part of a World Heritage Site and is subject to the strictest legal protections, so it would be highly unlikely that we would be able to access this type of material today. Getting access to the core drilled from Stone 58 was very much the Holy Grail for our research. Thanks to help from organisations such as the British Geological Survey and the Natural History Museum we have been able apply a suite of state-of-the-art techniques to it. This small sample is probably the most analysed piece of stone other than Moon rock!“ The research was given a nomination for The Current Archaeology Awards 2020, which celebrates projects covered by the magazine, highlighting those deemed to have made the most outstanding contributions to archaeology.

Where next for geological research on the Stonehenge stones? There are still many mysteries to be uncovered. “Although we now understand where most of the sarsen megaliths at Stonehenge originated, we still don’t know where two of the 52 remaining sarsens at the monument came from,” says David Nash. “These are upright Stone 26 at the northernmost point of the outer sarsen circle and lintel Stone 160 from the inner trilithon horseshoe. It is possible that these stones were once more local to Stonehenge, but at this stage we do not know. We also don’t know the exact areas of West Woods where the sarsens were extracted. Further geochemical testing of sarsens and archaeological investigations to discover extraction pits will be needed to answer these questions.” 

_______

You can listen to Dave Nash talking about his Stonehenge discovery to our Brains at the Bevy audience, along with other exciting talks, by visiting our .

Professor David Nash with the core sample drilled from Stone 58. (Image courtesy of Sam Frost, English Heritage.)