At first glance this little stone could easily be dismissed – especially if you have been spoilt by all the magnificent agates from elsewhere in America. But two facts make these Wisconsin Fluorite thundereggs stand out spectacularly. The first is that, as the name suggests, they are one of the few locations that are often filled with something other than agate/quartz. The other is their age. With Oregon thundereggs dated at about 30 million years old and European stones up to 300-450 million years old, it comes as quite a shock to realise that these little fluorite thundereggs are a staggering 1.1 billion years old. That dates them right back to the Pre-Cambrian period and roughly to the time of the first multicelular life on the planet.

Such thoughts make the head spin. Just about the entire development of life, the first structures, the first ‘creatures’, the colonisation of the land, extinctions and evolution, over and over – throughout pretty much the entire history of life on this planet, these little rocks have been sitting there quietly in the ground. Suddenly it seems as though these extraordinary thundereggs should be the centrepiece of a collection, not some curious extra. This is the ur-thunderegg, at least to our imperfect perception.