What is the term for the sparkle that occurs in a diamond when the gem, light source, or observer move?

The term for the sparkle that occurs in a diamond when there is movement of the gem, light source, or observer is referred to as scintillation. Scintillation describes the flashes of light that can be seen when a diamond is moved or when an observer shifts their angle of view. This phenomenon results from the diamond's facet structure reflecting light in various directions, creating a dynamic interplay of brightness and sparkle as the light catches different facets.

The other terms have distinct meanings: fire relates to the color flashes produced when light disperses through the diamond, brilliance describes the overall white light return of a diamond, and dispersion specifically refers to the separation of light into its spectral colors. Understanding these differences helps clarify why scintillation is the correct answer in the context of movement triggering sparkle in a diamond.