Ammolite Sterling Silver Stud Earrings. Tre round-shaped ammolite gemstones are set in .925 sterling silver. Ammolite is a gemstone that is formed from the fossilized shells of extinct ammonite mollusks. Ammolite is primarily composed of aragonite, the same mineral that makes up pearls and the inner shells of some mollusks. The gemstone is known for its vivid and iridescent colors, which are created by the refraction and reflection of light as it passes through the thin layers of aragonite that make up the gemstone.