Quartz (also known as rock crystal) is the commonest gem on earth, and is found on every continent. It can take many forms. Many gems we know as other gemstones belong to the quartz family. Some of these are amethyst, citrine, Herkimer, smokey quartz, rose quartz, aventurine, prase, tiger's eye, and amatrine. The name is derived from the Greek word krustallos, meaning ice, because they thought it was ice formed by the gods. Quartz has been thought to have mystical properties. Since the Middle Ages mediums have used crystal (quartz) balls to tell the future. And early American cultures carved crystal skulls over 1,500 years ago to use in religious ceremonies.
The most common type is clear quartz, Silicon Dioxide, with a hardness of 7 on the Mohs scale. (Diamond is the hardest gemstone with a hardness of 10). It has a hexagonal structure, or is six-sided (there are some varieties that are trigonal).
Quartz exhibits characteristics of piezoelectricity, meaning it can transform mechanical energy such as pressure into electric energy and vice-versa. The word piezoelectricity means electricity resulting from pressure. You can also cause quartz to vibrate when a small amount of electricity is applied. When I worked in electronics we used tiny quartz crystals, receiving a tiny amount of electricity, to work as counters, because of their dependable vibrational qualities. Most people know about their use in watches. In the 1930's and 1940's they were used in radios (known as crystal radios) and in microphones.