‘Polissoir’, discovered in Valley of Stones nature reserve, was used about 5,000 years ago to hone tools such as axes

At first glance it looked like nothing more than a rugged boulder jumbled among many others on the floor of a valley in the West Country.

But a smooth, glossy dip in the stone indicated that it was something very special – a vanishingly rare “polissoir”, or polishing stone, used 5,000 years ago by Neolithic people to hone tools such as axes.