Ammolite is a fossilized shell that can display which optical property?

• A. Opalescence
• B. Luster
• C. Fluorescence
• D. Iridescence

Answer: (D)

Iridescence is the optical property that causes colors to shift with the viewing angle. Ammolite, a fossilized ammonite shell, preserves nacre—layers of thin aragonite platelets. When light hits these layered structures, reflections from multiple interfaces interfere. Depending on the angle, some wavelengths reinforce while others cancel, producing a vivid, angle-dependent rainbow. That dynamic color change is the essence of iridescence, which is why ammolite is prized for its vibrant play of color. Opalescence would be a milky, opal-like glow without strong angle-dependent shifts; luster is just the surface shine, and fluorescence is light emission after UV exposure, not the changing color with angle shown by ammolite.