This is “coprolite”: fossil feces, dinosaur dung, petrified poop… rocks tens of millions of years old…the fossilized leavings of dinosaurs and other extinct animals. Like all petrified fossils, coprolite is made of different materials, depending on what the medium of petrification was. On the left, the agate-like material has been sliced and polished from a larger chunk. On the right, a small pyramid of spheres is made of Alabama marcasite. They are enlarged about twice life size.
Counter to what some folks might say, you can polish a turd. 🙂