Quartz is a silicon crystal usually occurring in the form of druzy, 6-sided prisms, or massive crystals and it is the second-most abundant mineral on earth. It has been most commonly used for carved art and for jewelry, though their piezoelectric abilities are also highly useful. Its clear form is often referred to as "rock crystal," and ancient philosophers once thought it was a form of supercooled ice. Though this product is the rock crystal form of quartz, quartz also comes in the forms of agate, amethyst, aventurine, carnelian, chalcedony, citrine, jasper, milky quartz, onyx, prasiolite, rose quartz, rutilated quartz, smoky quartz, and tiger's eye.
Rock crystal quartz is an invaluable component of the crystal oscillator, which is invaluable to precise timekeeping devices and solid state electronics. One of the first contexts for this use was as a phonograph pickup. Additionally, due to its triboluminescent properties, quartz crystals were collected and used by the Ute people of Colorado to generate flashes of light in night ceremonies. It is thought that quartz may be the maban stone of Aboriginal Australian lore. In Ireland, it is referred to as "sun stone," possibly because of it's ability to split light into a spectrum.
Rock crystal is, in fact, the traditional material of crystal gazing balls. According to The Book of Talismans, Amulets, and Zodiacal Gems by William Thomas and Kate Pavitt, because of the Moon's rule over the sign of Cancer and powers of intuition, rock crystal/clear quartz is thus a stone well-matched with Cancer.
Possible correspondences: abundance, Cancer, earth, electricity, ice, light, lightning, mechanics, multiform, precision, resonance, sound, sun, technology, water.