A piece of one of the enormous sarsen stones at Stonehenge has been returned to the ancient monument, English Heritage has announced. The prehistoric stone ‘core’ was removed during archaeological excavations in 1958 and its existence remained largely unknown for the next 60 years. The core will now join English Heritage’s collection of more than 500,000 artefacts and may help to uncover the source of the stones that form the instantly recognisable trilithons and outer circle of Stonehenge.

In 1958, archaeologists raised an entire fallen trilithon. During the works, cracks were found in one of the vertical stones and in order to reinforce it, cores were drilled through the stone and metal rods inserted. The repairs were masked by small plugs cut from sarsen fragments found during excavations and are very hard to see today.

The work was undertaken by a diamond cutting business called Van Moppes, a Basingstoke company. Three 32mm holes were drilled horizontally through the one metre thick stone. An annular drilling machine was used to bore out the holes, which resulted in three cores of approximately 25mm diameter being extracted. A watercolour illustration from the time shows the proceedings.

A Van Moppes employee, Robert Phillips, kept one of the stone cores and for a number of years, this unusual 108 cm long piece of Stonehenge took pride of place in his office. When Robert left the firm in 1976 and later emigrated to the USA, the core travelled with him, from Rochester, New York to Chicago, Illinois, to Ventura, California and finally Aventura, Florida. However on the eve of his 90th birthday, Robert expressed his desire that this prehistoric fragment be returned to the care of English Heritage, the conservation charity who look after the ancient stones. Last year, Robert’s sons, Robin and Lewis, travelled to Stonehenge and presented it to English Heritage curator, Heather Sebire.

Whether the other two Stonehenge cores survived remains unknown. English Heritage would like to hear from anyone who was involved – or whose family was involved – in the archaeological excavations at Stonehenge during the 1950s and who has more information as to the remaining cores’ whereabouts. They can get in touch by emailing stonehenge.core@english-heritage.org.uk.

This recently returned piece of Stonehenge, which looks incongruously pristine next to the weathered stone from where it came, may now help locate the original location of the sarsen stones. Stonehenge’s smaller bluestones were famously brought from the Preseli Hills in south-west Wales but the precise origin of the much larger sarsens is unknown. A British Academy and Leverhulme Trust project, led by Professor David Nash of the University of Brighton, is investigating the chemical composition of the sarsen stones at Stonehenge in order to pinpoint their source. The project team have already used a handheld portable spectrometer to investigate the chemistry of the sarsen stones at Stonehenge using x-ray fluorescence, a non-destructive technique. The core presents the team with a unique opportunity to analyse the unweathered interior of a stone.

Heather Sebire, English Heritage’s curator for Stonehenge, said: “The last thing we ever expected was to get a call from someone in America telling us they had a piece of Stonehenge. We are very grateful to the Phillips family for bringing this intriguing piece of Stonehenge back home. Studying the Stonehenge core’s ‘DNA’ could tell us more about where those enormous sarsen stones originated. The other two Stonehenge cores may still be out there somewhere and if anyone has any information, we’d love to hear from them.”