Quartz can produce an electrical reaction. Minerals with this ability are called piezoelectric. The electrical reaction can be created by applying a charge, physical stress, or heat. Quartz is also distinguished as a gem that is capable of triboluminescence, or the ability to create light under pressure. This mystery light is not electricity in the form that we know it, but it is often mistaken as such. The most prominent scientific theory is that it is caused by the separation of chemical and electrical bonds. Diamonds are actually insulators; they do not conduct electricity.