What causes a diamond to have what most people call Sparkle. It is the combined effect of contrast among the high intensity and low intensity reflections of light to the eye from the different Facets, when the diamond moves under a light, or the lights move around a diamond.

One of the three main considerations of a diamond’s Light Performance: Scintillation, Brilliance and Fire.

I found this rotating diamond illustration on the web, years ago, which shows the effect of scintillation ::

spinningdiamond

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