Long-lost fragment of Stonehenge gives unprecedented look inside ancient monument

A long-lost fragment from Stonehenge, recovered by the man who was conducting restoration work on the monument, has been recovered after 60 years, giving scientists a first look inside the column of the iconic monument.

In 1958 Robert Phillips, a representative of the drilling company that helped to restore Stonehenge, took the cylindrical core after it had been drilled out of one of Stonehenge’s pillars, Stone 58. Later, when he emigrated to the United States, Phillips took the core with him.

Because Stonehenge is protected, it is no longer possible to extract samples from the stones. But after the core returned in 2018, researchers had the opportunity to conduct an unprecedented geochemical analysis of the Stonehenge pillar, the results of which they described in a new study.

They found that the standing stones, or sarsens, towering over Stonehenge were made of rock containing sedimentary rocks that formed when dinosaurs walked the Earth. Other grains in the rock are up to 1.6 billion years old.

“We did computer tomography of the rock, X-rayed it, examined it under various microscopes and analyzed its sedimentology and chemical composition,” said lead author David Nash, a professor of physical geography at Brighton University in England.

“With the exception of thin section analysis and a couple of chemical methods, all of the methods we used in the study were new to both Stonehenge and the study of sarsen stones in Britain,” Nash told Live Science in an email.

Stonehenge’s central circle of pillars was erected during the Neolithic period, about 2,500 years ago, according to English Heritage, a nonprofit organization that manages historic monuments in England.

“Sarsens were erected in two concentric shapes – an inner horseshoe and an outer circle – and bluestone [small monument stones] were set in a double arc between them,” according to English Heritage’s website.

When scientists examined thin slices of sarsen rock from Stone 58 under a microscope, they were surprised to find that the stone was 99.7 percent quartz. The quartz “cement” held the small and medium-sized quartz grains together and formed “an interlocking mosaic of crystals,” Nash says.

This made the stone more durable, and may be why the builders chose this type of stone for their massive monument thousands of years ago.

“These cements are incredibly strong. I wonder if the builders of Stonehenge could have said something about the properties of the stone and chosen not only the nearest, largest boulders, but the ones most likely to stand the test of time,” Nash said.

Older than dinosaurs

The researchers’ analysis also revealed the age of sediments in the rock.

“The sandy sediments in which the rock formed were deposited during the Paleogene period, 66 to 23 million years ago, so the sarsens may not be older than that period,” he explained.

However, when scientists compared the ratio of neodymium isotopes – or atoms of the element with different numbers of neutrons in the nucleus – in the samples, they found that some of the deposits in the sarsen stone were even older.

Some of the sand grains were probably weathered from rocks dating back to the Mesozoic era (252-66 million years ago), when they may have been trampled by dinosaurs. And some of the sand grains were formed as early as 1-1.6 billion years ago.

While this analysis has answered some questions about Stonehenge, other unresolved mysteries remain, including the location of two other cores that were drilled from Stone 58 during the 1958 restoration that also disappeared.

Workers at the Salisbury Museum in England discovered part of one of these cores in their collection in 2019, researchers report. Museum director Adrian Green contacted English Heritage and reported the discovery of part of the stone 58 core “in a box labeled ‘3x Stonehenge Stones from ‘Treasure Box,'” the study said.

Scientists examined the fragment from Salisbury along with the core from Phillips and recorded its data in their study. However, “how and when it ended up in the museum is unknown,” the authors write.

The location of the third core (and the other cores that were in the Salisbury Museum) “is also unknown,” the scientists said.

The findings were published Aug. 4 in the journal PLOS One.

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