Triboluminescence is the effect where crystals are scratched or broken emit light. This can be demonstrated using wintergreen lifesavers. Simply crush a wint-o-green lifesaver with your teeth, a pair of pliers, or a hammer. In the instant that it is cracked, it will emit a flash of blue light.
When a sugar crystal is stressed, the positive and negative charges in the crystal are separated, generating high voltage. When enough charge has accumulated, the electrons jump across a fracture in the crystal, colliding with and exciting electrons in the nitrogen molecules in the air creating UV light. All sugar is triboluminescent, but the wintergreen mint (methyl salicylate) is fluorescent. Most of the light emitted by broken sugar is ultraviolet, and the fluorescent mint converts it to visible blue light.
