For example, a diamond may begin to glow while being rubbed. This occasionally happens to diamonds while a facet is being ground or the diamond is being sawn during the cutting process. Diamonds may fluoresce blue or red.
When you crush sugar crystals, tiny electrical fields are created, separating positive and negative charges that then create sparks while trying to reunite. WintOGreen Lifesavers work especially well for creating such sparks, because wintergreen oil (methyl salicilate) is fluourescent and converts ultraviolet light into blue light.