New Hampshire State Gemstone
Quartz is the most common mineral found on the Earth’s surface, and the second most abundant mineral in the Earth’s crust after feldspar. Quartz composes an estimated 12 percent of the continental crust; it makes up less of the oceanic crust. Made of silicon and oxygen, quartz occurs in basically all mineral environments and is a component of many rocks and the inner layer of many geodes.
Quartz is found in an impressive range of varieties and colors, including purple, rose, black, yellow, brown, green, and orange, and can also be colorless or multicolored. The main varieties of quartz are chalcedony, agate, amethyst, citrine, rose quartz, rock crystal, smoky quartz, milky quartz, rutilated quartz, onyx, tiger’s eye, and aventurine. Smoky quartz is the translucent brown, smoky gray, or black variety.
The color is caused by the irradiation, whether natural or artificial, of rock crystal. Smoky quartz itself has several varieties, including cairngorm, a variety that comes from the Cairngorm Mountains in Scotland; morion, a very dark black opaque variety; coon tail quartz, a variety with an alternating black and gray banding; and gwindel, a cluster of nearly parallel crystals.
The varieties of quartz are classified as either macrocrystalline, meaning its crystals are large and visible to the naked eye, or cryptocrystalline, meaning it has crystals so small they are not visible by a microscope.
New Hampshire designated smoky quartz its official state gem in 1985. The mineral is common in the state.
The word "quartz" comes from the German quarz, which is of Slavic origin (Czech miners called it křemen) and means "hard."
FORMATION AND OCCURRENCE
Quartz commonly occurs with igneous rocks such as granite, sedimentary rocks such as sandstone and shale, and metamorphic rocks like schist, gneiss, and quartzite. Its resistance to weathering makes it also common in stream sediments and residual soils. Quartz occurs in hydrothermal veins along with ore minerals.
Quartz is extraordinarily common and found all over the world. Some of the more noteworthy locations for smoky quartz include the Pikes Peak area of Colorado, the Swiss Alps, and Brazil.
Early civilizations believed that quartz crystals were permanently frozen ice. Quartz’s high thermo-conductivity, which makes it feel cool to the touch, may have added to this belief. Regardless of what early people may have believed, historical records show the use of rock crystal for decoration and jewelry for at least 4,000 years. Tools and weapons were made from rock crystal long before it was used for decoration and jewelry.
For centuries in Europe and the Middle East, the diverse varieties of quartz were the most common semi-precious stones used in jewelry and carving. Valuable objects including engraved gems, cameos, and extravagant vases and vessels were carved from the stone.
Nicolas Steno, who is considered the father of geology, paved the way for modern crystallography with his studies of quartz in the 17th century. Steno discovered that no matter how distorted a quartz crystal, the long prism faces always make a perfect 60-degree angle.
Sand is composed of tiny quartz pebbles, and is the primary ingredient in manufacturing glass. Transparent rock crystal is used in the study of optics. Quartz is also used as an abrasive for sandblasting, grinding glass, and cutting soft stones. Quartz is essential in the computer industry, since silicon semiconductors are made from the mineral.
Quartz crystals are piezoelectric, which means they develop an electric charge with mechanical stress. This property was employed in phonograph pickups using quartz crystals, and for decades quartz has been used as a crystal oscillator in quartz clocks, watches, radios, and pressure gauges. In addition, quartz is important in the production of soaps and ceramics.
In the gem industry, many varieties of quartz are cut as faceted stones. One of the most popular gems, quartz is often cut as a brilliant round to maximize the color. Colorless stones can be heat-treated, irradiated, or dyed to enhance the color. Amethyst is the most popular quartz gem, and citrine is the most valuable. Rose quartz, smoky quartz, rock crystal, and aventurine are also cut into gems. The black and white combination of rock crystal and onyx was popular in art deco jewelry design.
Quartz specimens are very popular with mineral collectors. Some collectors specialize their entire collections on different types of quartz.
Quartz varieties are usually quite harmless unless broken or powdered. Broken crystals may have razor-sharp edges that can easily cut skin. Long-term exposure to finely ground amethyst powder may lead to the lung disease silicosis.
Quartz has long been thought to have mystical and magical properties. Rock crystal and smoky quartz were once used for crystal balls by fortunetellers and witches. But since large, flawless specimens of rock crystal are rare, crystal balls are now made of glass. During the late 1980s and early 1990s, metaphysical uses and applications of rock crystal resulted in an increase in its production and processing. The metaphysical market used raw crystal in jewelry, personal power devices, and healing devices. Spheres, skulls, pyramids, and other metaphysical objects were made from rock crystal. The metaphysical market has declined from its peak and now appears to have stabilized.
Smoky quartz is said to enhance endurance. It is believed to be grounding, and to improve one’s organizational skills. Some believe that a clear quartz crystal pendant will bring the wearer good luck.
SUBSTITUTES / SYNTHETICS
One of the first gems to be synthetically grown on a large scale was quartz. This industry was largely developed during World War II to supply crystals for radios. Today synthetic quartz is used extensively in the electronics industry.
Chemical Formula: SiO2
Crystal Structure: Trigonal
Hardness (Mohs): 7; lower in impure varieties
Color: clear (in pure form)
Birefringence: +0.009 (B-G interval)
Refractive Index: 1.544-1.553 - Dr +0.009 (B-G interval)
Density: 2.65 constant; variable in impure varieties
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press