What is an optical phenomenon? Plainly put, this term embodies the result of the way light interacts with the crystalline structure, inclusions, and/or internal structure of a gemstone. It is, in essence, the reflection, diffraction, absorption, and/or diffusion of that light. Without even knowing, we encounter these phenomena on a daily basis, whether in opal, moonstone, alexandrite, or cat’s eye chrysoberyl—that said, one should be careful not to confuse optical property, such as dispersion in a diamond, with optical phenomena.
This article will explore optical phenomena in gemmology, offering an explanation as to why and how it occurs, expanding this knowledge, and helping jewellers better explain the wonders of gemstones to their clients.