Sea UrchinThis sea urchin fossil preserves the hard, calcite skeleton (test) of an echinoid, a marine invertebrate related to starfish and sand dollars. Fossils like this provide valuable insights into ancient marine environments and the evolutionary history of echinoderms, which have existed for over 450 million years. Features: Composition: The fossilized test is primarily composed of calcite, a crystalline form of calcium carbonate (CaCO), which often