Analyzing the Architecture of Stonehenge: From Bluestones to Sarsens
While studies have traced the smaller stones near the center of Stonehenge, known as bluestones, to the Preseli Hills in Pembrokeshire, over 200 km (124 miles) away, the origin of the site's largest stones, known as sarsens, has remained a mystery.
But new research from four UK universities (Brighton, Bournemouth, Reading, and UCL) and English Heritage, the organization that cares for Stonehenge, reveals a likely source. The research team used a novel geochemical approach with X-ray fluorescence (XRF) technology to determine the location.
The results show the large sarsen stones came from a much more local area—the West Woods, Wiltshire, just 25 km (15 miles) north of the monument.
Tracing the Source of Giant Sarsen Stones Using XRF Technology
First, the researchers analyzed the 52 sarsens at the Stonehenge monument using our Olympus DELTA handheld XRF analyzers.
For those who are unfamiliar, XRF analyzers use a nondestructive technique called X-ray fluorescence to determine the elemental composition of a material without damaging it. It works like this: when you run a test, the analyzer emits X-rays that hit the sample, causing the elements in the sample to fluoresce and send X-rays back to the analyzer's X-ray detector. The analyzer then measures the energy spectrum and provides the chemistry result on the screen. All of this happens in seconds.
As fast, portable instruments, XRF analyzers enable archeologists to analyze large, heavy samples (like sarsens) without needing to bring them into the lab. As a result, researchers can get immediate, lab-quality results in the field.
The XRF results, now published in the journal Science Advances, show that 50 of the sarsens share a similar geochemistry. This meant they originated from one common source.
While Stonehenge scholars long suspected the sarsens came from nearby Marlborough Downs, an area with the largest concentration of sarsen in the UK, the scientists needed a way to confirm the source and pinpoint a more exact location. After all, the Marlborough Downs covers a wide area, and other regions with sarsens, such as Kent, Dorset, and Oxfordshire, could have supplied the stones.
The answer came to them when something unexpected happened—a missing part of Stonehenge was returned to the UK.
So, how did a piece of Stonehenge go missing in the first place? The mystery began in the 1950s.
In 1958, drilling work was completed at Stonehenge to help re-erect a fallen trilithon, a structure made of two upright sarsens covered by a sarsen lintel stone. During the process, the workers removed three one-meter-long (3 ft) drilled-out cylinders, known as cores, from one sarsen stone (Stone 58) to stabilize it with metal rods. While scientists knew analyzing the cores could potentially lead to the origin of the stones, there was one problem—all three cores had gone missing.
For 60 years, the whereabouts of the cores remained a mystery.
In 2018, that all changed. Englishman Robert Phillips, one of the restorers involved in the drilling work, returned one of the cores to the UK right before his 90th birthday, enabling researchers to perform tests on the complete yet fragmented core sample. He had been given the core as a souvenir of the conservation work and had kept it first at his UK office and later at his home in Florida.
A year later, part of the second core turned up at the Salisbury Museum. Today, the rest of the second core and the third core have yet to be found.
Solving the Stonehenge Mystery with Geochemical Fingerprinting
With the "Phillips' Core" returned, researchers could get back to work. The goal was to determine the unique geochemistry, or the geochemical fingerprint, of the sarsen core and match it to the geochemical fingerprint of sarsens across southern Britain.
Since sarsens are mostly made of silica, the geochemical fingerprint would be made of the remaining elements (the trace elements). These trace elements vary depending on the sarsen location, so finding a match would enable them to pinpoint an exact source.
With permission from English Heritage, scientists at the University of Brighton first cut three small samples from a section in the middle of the Phillips' Core. These samples were tested with two technologies, inductively coupled plasma mass spectrometry (ICP-MS) and ICP–atomic emission spectrometry (ICP-AES), to determine the trace elements and construct a geochemical fingerprint for Stone 58.
When the fingerprint was compared to equivalent ICP-MS and ICP-AES data collected from sarsen samples in 20 regions across southern England, it matched the West Woods in the southeast Marlborough Downs.
This discovery provides some additional insight into the historic monument, but it also brings up new questions:
- Why did the early inhabitants choose the West Woods area as the primary source for the Stonehenge sarsens?
- Where were the sarsens extracted from in the West Woods?
- Why were two of the 52 sarsens taken from a different source, and where did they come from?
To answer them, archaeologists will need to continue their research using advanced technologies like XRF.
To learn more about the role of Olympus XRF analyzers in this breakthrough and other discoveries, read more about the research project and explore the applications of our newest handheld XRF instrument, the Vanta analyzer.