At first sight, this is surely a piece of contemporary sculpture, carved from white stone. But it’s completely natural, formed millions of years ago in northern France, when superhot water filtered through ancient dunes of pure sand, cementing the grains together into these fluid lines – the curve of an earlobe, blobs of Tippex, contour lines on a map, a fist of knuckles. Whatever you see in there, it’s all from natural processes, not from human endeavour.

This example was donated to the Museum to mark David Attenborough’s 90th birthday. It’s fun to watch object stopping visitors in their tracks as they pass through the museum. They’re rarely sure what they’re looking at.