Researchers studied a drill core extracted from Stone 58 in the 1950s while working to preserve Stonehenge. This pulp was kept in the US for decades until it was returned to the UK for research in 2018.
Megaliths were made from a stone called silcrete – sarsen is the slang for silicon concrete. The silicon concrete layer slowly forms a few meters below the earth’s surface due to groundwater intrusion through the sediment.
The investigation revealed the internal structure of stone 58. It showed that silicon concrete consists mainly of quartz sand grains, held together by an interlocking mosaic of quartz crystals. Quartz is especially durable: it does not crumble easily and does not erode very much, even if it has been exposed to wind and weather for centuries.
“This explains the stone’s weathering resistance and why it is an ideal material for building a monument,” said geomorphologist David Nash of the University of Brighton. Nash was responsible for the new study.
It is not clear when exactly the stone was formed. The researchers found that some grains of sand from the thin concrete layer date back to the Mesoproterozoic era, 1 billion to 1.6 billion years ago.
