A team of scientists from the University of Bristol in the UK has gotten closer to solving an ancient mystery central to the country’s most famous archaeological site thanks to a “Holy Grail” core sample that has waited nearly 60 years to reveal its crystalline clues. 

Led by Professor David Nash, the researchers were able to analyze two pieces of slab with help from the British Geological Survey, London’s Natural History Museum, the Salisbury Museum, and English Heritage.

One sample was returned by the family of a man named Robert Phillips who had removed it while working on the site as a stonecutter in the late 1950s. 

“Getting access to the core drilled from Stone 58 was very much the Holy Grail for our research,” Nash said in a statement. “It is extremely rare as a scientist that you get the chance to work on samples of such national and international importance.”

The analysis of the samples revealed that the sarsen had an interwoven quartz crystal core which makes the ancient slabs nearly indestructible, according to the researchers. 

The structural analysis expands on Nash’s recent findings that pinpointed the outer stones’ origins to the West Woods section of Marlborough Downs. The area had long been held to be the source for material used to construct the site, which was put together in two phases by unknown local workmen between 4,500 and 5,000 years ago.

Only rabbits and other small animals pose a threat to Stonehenge, according to Nash. A court order has also recently halted a potentially damaging highway project near the site. Artnet has more on the discovery here.