Which term describes the visual effect of a diamond's surface sparkle?

The term that accurately describes the visual effect of a diamond's surface sparkle is brilliance. Brilliance refers to the light that is reflected from the internal and external surfaces of a diamond. It's a measure of how much white light is returned to the eye from the stone, which contributes significantly to a diamond's overall appearance. This sparkle is primarily influenced by the diamond's cut, as the angles and proportions of its facets determine how well it can reflect and refract light.

While "icing" is a term sometimes used informally to refer to the appearance or surface of a diamond, it does not have a standardized definition in gemology and is not recognized as a technical term. Fire refers to the colorful flashes of light that appear when a diamond disperses light into different colors, and dispersion is the phenomenon that causes the separation of light into its spectral colors. Therefore, though related to light interaction, these terms focus on different aspects of a diamond's optical performance and do not specifically capture the surface sparkle effect described.