The earliest grain mills used large round stones to grind the grain. (sourdoughhome.com)
Most of us have seen pictures of the Mayan calendar at some point: that round stone disc carved with a dense assortment of creepy - looking faces and strange symbols. (fieryfoodscentral.com)
Sometimes, the bile ducts are full of cholesterol crystals that did not form into round stones. (healingdaily.com)