Two Quartz rocks which have piezoelectric properties. Hit them together and generate light and sparks.

Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress. The word is derived from the Greek piezein, which means to squeeze or press. The effect is reversible; piezoelectric crystals, subject to an externally applied voltage, can change shape by a small amount. The effect is of the order of nanometres, but nevertheless finds useful applications - for example fine focusing of optical assemblies, etc.

WHAT TO DO: Put a rock in each hand and hit them hard against each other in a dark room or outside in total darkness. You will see light and sparks generated by the rocks at the point of impact.

• Included are two (2) Quartz piezo electric rocks.
• Each about 1 inch in diameter