Never seen a gogotte before? Also known as concretions, some of the most mesmerizing examples come from the Fontainebleau region in France. 

Fontainebleau was covered in water around 30 million years ago, and when it disappeared, it left behind a layer of quartz. Silica-rich water from the environment then flowed through the layers and the silica bonded quartz like glue, turning loose sand into hard sandstone. The result is swirling mineral formations whose unique shapes were sculpted over millions of years’ worth of geological and chemical processes.

In a similar manner to how we might think a cloud looks a bit like a dog, gogottes have also become the subject of pareidolia – detecting a meaning or pattern when there is not one. In addition to their unusual formation, this has made gogottes highly sought after; France's King Louis XIV reportedly had several specimens dotted about the gardens at the Palace of Versailles.

This article first appeared in Issue 24 of our digital magazine CURIOUS. Subscribe and never miss an issue.