Here’s some geology for a change.
At Slättemossa in the province of Småland, southern Sweden, are found ice-polished outcrops of orbicular diorite (“Napoleonite”). This rock consists of granite balls covered with hornblende and other minerals and then encased in a granite matrix. When the inland ice ground the rock down, a smooth grey surface covered in darker circles resulted. Pretty striking, as seen in the photographs by Anders Möller! Anders and Inger are badass geocachers, having found nearly 1400 caches and hidden more than 200.