The analytical work that matches up the samples of rock at Stonehenge with those taken from rocks in north Pembrokeshire has been done by Dr Nick Pearce, Reader in Geochemistry at the Institute of Geography and Earth Sciences at Aberystwyth University. Dr Pearce and colleagues at the Institute have pioneered a technique which uses laser to vaporise minute samples of rocks so that their chemical composition can be determined. In the case of the samples from Stonehenge and Pembrokeshire, Dr Pearce focused on the geochemistry of tiny grains of the mineral zircon that are embedded within the rocks. Measuring between 50 and 100 microns across and invisible to the naked eye, the grains of zircon were selected by looking at highly polished transparent slices of the rock samples under a microscope. Once identified, part of the zircon was vapourised by a powerful laser beam measuring just 10 microns– 100th of a millimetre- across and analysed in a mass spectrometer.

Just like matching fingerprints, the chemical composition of the zircons in both samples was indistinguishable, proving beyond reasonable doubt that the source of the rhyolites at Stonehenge is indeed a rocky outcrop at Pont Saeson on the northern side of the Preselai.The technique used by Dr Pearce in this study was developed to look at the chemical composition of tiny grains from fine layers of volcanic ash. The precise date of the eruption of Santorini around 1630BC has been the subject of much debate and this technique has been used to confirm or refute the identity of ash samples collected from around the world and thought to originate from Santorini.