Ammonites are prized for their beautiful fossilised shells, which display stunning iridescence and intricate, chambered structures. Their shells can be stone-like, opalised or composed of aragonite, a crystalline form of calcium carbonate. 
 
Sea Urchin Fossils (Echinoderms) first appeared around 540 million years ago. They are found as fossils in rocks of all ages and are still common in oceans across the world.