Crackle quartz is a crystalline quartz that has been intentionally fractured by people. They usually heat rock crystal or slightly translucent quartz to a high temperature, then suddenly quench it in cold water. The shock of sudden cooling causes a network of tiny fractures to propagate through the quartz. The result is a transparent colored stone that sparkles when it is moved under bright light. The sparkles are produced as light enters the stone, strikes an internal fracture surface, and reflects back to the eye of the observer.