The sparkle of a polished or metal object. This should come from a physical object, such as jewelry, a sword, or teeth.
Sparkle, glint, and diffraction spikes all refer to similar patterns of bright lines radiating from a point. They are not clearly differentiated, and usage tends to be context-sensitive. In general:
Sparkle is considered the base case. Usually four lines at right angles radiating from a point. Associated with eyes, liquid or particulate matter (e.g. raindrops, snow, sand), or nothing (appearing mid-air). Can appear in large numbers.
Glint is associated with solid objects, especially ones which are metallic and/or sharp. Usually appear singly or in small numbers.
Diffraction spikes is the technical term for the phenomenon in general, but is used less often. Can be used for more realistic-looking effects or conversely when appearing extremely large and exaggerated. More likely than sparkle and glint to be asymmetric or to have more than four radiating lines.