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

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

Answer: (C)

Iridescence is produced when light interacts with the layered nacre (mother-of-pearl) in ammolite. The fossilized shell has thin aragonite platelets stacked with organic material, causing light to reflect and interfere across those layers. As you change the viewing angle, different wavelengths interfere constructively, so the colors shift and shimmer—bright greens, blues, reds, and purples that seem to glow from within. This angle-dependent color change is the hallmark of iridescence.

Opalescence would be a more diffuse, milky glow that doesn’t shift with angle in the same vivid way. Fluorescence involves emitting light after being excited by UV, which isn’t the typical display for ammolite. Chatoyance creates a cat’s-eye band of light across a gemstone, which ammolite does not exhibit. So the best match for ammolite’s optical display is the shifting, rainbow-like iridescence produced by its nacreous structure.