An extremely rare and important stone artefact dating back over 5,000 years has been discovered during a community heritage project in West Dorset.

The natural stone boulder has a dished glossy surface where it was used to polish stone axe heads over 5,000 years ago. It has been discovered in the Valley of Stones National Nature Reserve in the Dorset Area of Outstanding Natural Beauty (AONB), near Bridport.

In addition to being on a Site of Special Scientific Interest (SSSI), the polishing boulder is located within an area protected as a scheduled monument.

The polishing boulder – known as a polissoir - is formed of sarsen stone, a particularly hard form of sandstone known as silcrete (a cemented mass of sand and gravel), that was used during the Neolithic period for building monuments such as Stonehenge.

Sarsen boulders are found across southern England, but out of nearly 1,000 that have been examined by experts, including Dorset's sarsens, very few are known to have been used for polishing stone tools.

This is a very rare discovery, being only the second undisturbed, polissoir found in its original position in England.

The community archaeology company Past Participate CIC was leading a survey funded by the Farming in Protected Landscapes Fund, administered by Dorset AONB, to locate sarsens in West Dorset when volunteers from the conservation group EuCAN, working with Natural England, contacted them about an area of the nearby Valley of Stones.

The area had recently been cleared of vegetation, revealing sarsens that had not been visible for decades. An examination of these sarsens led directly to the discovery of the polissoir.

Stone axes were essential tools for the early farming people of the Neolithic to clear woodland and build houses and monuments, and axes were made of various raw materials such as flint, volcanic tuff and granite.

There is evidence that many of these stone axes travelled widely in prehistoric times, whether they were traded as part of exchange systems or carried by their owners from distant sources where the stone was quarried.

For felling trees and working with timber, the stone axe heads would have been attached to a wooden handle, but this part of the tool very rarely survives.

Following the discovery of the polissoir, the immediate area around the stone has been subject to excavation and specialist analysis to see if any traces of the makers of the stone axes are still present.

The excavation is the result of a collaboration between Past Participate CIC, Historic England and Natural England, together with local volunteers who have been integral to this discovery.

Historic England has now started a programme of state-of-the-art research, which will examine the wider landscape over the next year to increase understanding of the prehistoric and historic features that remain.

Dr Anne Teather, director at Past Participate, said: "This incredible discovery represents the research value that community heritage projects can bring.

"We are grateful for the Farming in Protected Landscapes scheme for funding that stimulated these investigations into the Valley of Stones, and Historic England and local landowners for their support.

"We hope to secure further funding that will enable us to continue our work in this landscape with our committed team of volunteers."

Jim Rylatt, director of archaeology past participate, said: "Finding a polissoir was a very unexpected outcome of our sarsen survey. These stones rarely survive, but would have been extremely important to Neolithic people, as without axes they could not have cleared woodland and farming would have been impossible.

"Our investigation of the polissoir will provide important insights into the use of this landscape almost 6000 years ago."

Sasha Chapman, inspector of ancient monuments at Historic England, commented: "This is a hugely exciting and rare discovery in this little understood historic landscape, which is giving us an opportunity to explore the use of the stone, and the communities who were using it.

"Historic England has been pleased to support Past Participate who made the original discovery. Our scientists and landscape investigators are providing specialist expertise and advice to enable a better understanding and record of this unique site and its wider archaeological setting."

Rob Beard, reserve manager at Natural England, said: "We are really excited to be working with Historic England and Past Participate to find out more about how people have lived in, worked and shaped the historic landscape at the Valley of Stones for thousands of years.

"The wealth of earthworks and archaeological remains on the site have a fascinating and complex story to tell and we are really fortunate to have the experts working with us to interpret and understand more fully this special place and the people who made it."

Tom Munro, Dorset AONB manager, added: "We are delighted to have been able to support Past Participate's work in this area through the Farming in Protected Landscapes Fund which has led to this remarkable find.

"It's a reminder of the time depth of this nationally important landscape, and how human activity has shaped it for thousands of years. It's also a story about the connections between people, past and present, and the value of communities engaging with these very special landscapes."