What does the phenomenon refer to in gemology?

In gemology, the term "phenomenon" specifically refers to an unusual optical effect displayed by a gem. This can include a variety of effects that enhance the gem's visual appeal and can be due to its unique internal structure, inclusions, or the way light interacts with the material. Such optical effects can be captivating and are often a significant factor in determining the value and desirability of a gemstone. Examples of these phenomena include asterism, which produces a star-like effect, and chatoyancy, which creates a narrow band of light across the surface. Understanding these phenomena helps gemologists identify and appreciate the unique characteristics of different gemstones.