Oolite

Along the shores of ancient seas, small grains were pushed back and forth along the sea floor, and picked up concentric coats of deposition like the building up of a pearl. These spheres, called Oolites, were later cemented into solid rock by the building up of millions of years worth of sediments, and this is the result. Although technically not a fossil of a living plant or animal, they nonetheless were created in conditions similar to those that are responsible for fossil formation.