Quartz Glow Stones

These silicate rocks have special properties; they generate electricity. If you turn the lights off and knock them together, you’ll notice a green spark at the point of contact that illuminates the entire stone as it conducts the light. This is an example of the piezoelectric qualities that quartz and other crystalline substances have. When you put a piezoelectric material under mechanical stress, for example by hitting it, tiny electrical currents are created and build up within the material, sending positively and negatively charged molecules out of alignment. The sparks occur as they try to reunite. This can happen with other crystalline materials we are familiar with like sugar, some types of bone, and some ceramics. A similar light effect can be seen if you crush a sugarlump in the dark. 

The piezoelectric qualities of quartz also work in reverse; it will oscillate (vibrate) or expand and contract when exposed to different frequencies of electricity. This has been used in many interesting ways, most commonly the crystal oscillator. As it vibrates in such a precise frequency, it can be used to keep track of time as in quartz wristwatches or digital clocks in computers and mobile phones, or to provide a stable frequency for radio communications.