The long-lost fragment of Stonehenge, which was recovered by the person who carried out the restoration work on the monument, was returned 60 years later, giving scientists the opportunity to look inside the column of the iconic monument for the first time.
In 1958, Robert Phillips, a drilling company representative that helped rebuild Stonehenge, took a cylindrical core after it was drilled from one of Stonehenge's pillars, Stone 58. Later, when he emigrated to the United States, Phillips took the core with him.
Due to the fact that Stonehenge is under protection, the extraction of samples from the stones is no longer possible. But after the return of the core in 2018, researchers have the opportunity to conduct an unprecedented geochemical analysis of the Stonehenge pillar, the results of which they describe in a new study.
They found that the standing stones, or sarsens, towering over Stonehenge, were made from rock containing sedimentary rocks that formed when dinosaurs walked the Earth. Other grains in the rock are 1.6 billion years old.
"We took a CT scan of the stone, irradiated it with X-rays, examined it under various microscopes and analyzed its sedimentology and chemical composition," said lead author David Nash, a professor of physical geography at the University of Brighton in England.
“With the exception of thin section analysis and a couple of chemical methods, all the methods we used in the study were new to both Stonehenge and the study of sarsen stones in the UK,” Nash said in a letter to Live Science.
Stonehenge's central pillars were erected in the Neolithic era, about 2,500 years ago, according to English Heritage, a non-profit organization that manages historic sites in England.
The sarsens were erected in two concentric forms - the inner horseshoe and the outer circle, and the bluestones [small monumental stones] were placed between them in a double arc, "the website of the English Heritage organization says.
When scientists examined thin sections of sarsen rock from Stone 58 through a microscope, they were surprised to find that the stone was 99.7 percent quartz. The quartz "cement" held the fine to medium grains of quartz together and formed an "interlocking mosaic of crystals," says Nash.
This made the stone more durable, and perhaps that is why the builders chose this type of stone for their massive monument thousands of years ago.
"These cements are incredibly durable. I wonder if the builders of Stonehenge had something to say about the properties of the stone and select not only the closest, largest boulders, but also the ones that are most likely to stand the test of time," Nash said.
Older than dinosaurs
The analysis of the researchers also made it possible to find out the age of the deposits in the rock.
"The sandy deposits in which the stone formed were deposited during the Paleogene period, 66-23 million years ago, so the sarsens may not be older than this period," he explained.
However, when scientists compared the ratio of neodymium isotopes - or atoms of an 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 grains of sand were probably weathered from rocks dating back to the Mesozoic era (252-66 million years ago) when dinosaurs may have trampled them. And some grains of sand were formed 1-1.6 billion years ago.
While this analysis provided answers to some questions about Stonehenge, other unsolved mysteries remain, including the whereabouts of two more 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 say. Museum director Adrian Greene contacted an English heritage representative and reported the discovery of a piece of 58 "core in a box labeled" 3x Stonehenge Stones from "Treasure Box", the study said.
Scientists examined the Salisbury fragment along with the Phillips core and recorded its data in their study. However, "how and when he ended up in the museum is unknown," the authors write.
The location of the third core (and the rest of the cores that were in the Salisbury Museum) "is also unknown," the scientists said.
The results of the study were published on August 4 in the journal PLOS One.