Quartz

Background

caption Quartz crystals. (Source:Mineral Information Institute)

Quartz is a very common mineral in the Earth’s crust. Chemically, quartz is silica, or silicon dioxide, SiO2. It is found in most types of rocks: igneous, metamorphic and sedimentary.

Quartz is rather hard, 7 on the Moh’s hardness scale, and has a glassy (vitreous) luster. When a crystal is broken, the fracture surface is curved, like a shell. This is referred to as conchoidal fracture; glass fractures in the same way.

When crystallized in an open cavity in rocks, quartz forms easily-identifiable 6-sided (hexagonal) prismatic crystals. When formed without open spaces, deep within the earth, quartz crystallizes in small, roundish masses.

Quartz is physically and chemically resistant to weathering. When quartz-bearing rocks become weathered and eroded, the grains of resistant quartz are concentrated in the soil, in rivers, and on beaches. The white sands typically found in river beds and on beaches are usually composed mainly of quartz, with some white or pink feldspar as well.

Name

Because of its abundance and distinctive crystal shape, quartz has been recognized as a mineral for thousands of years. The name has an uncertain origin, possibly derived from the German word quarz, a word of ancient and uncertain origins.

When water-clear, quartz is known as rock crystal or mountain crystal. However, quartz can contain a number of different impurities, which create different color varieties. Purple quartz is known as amethyst; white is milky quartz; black is smoky quartz; pink is rose quartz, and yellow or orange is citrine.

As a mineral name, quartz refers to a specific chemical compound (silicon dioxide, or silica, SiO2), having a specific crystalline form (hexagonal). There are other forms of silica which are either non-crystalline, or of a different crystalline form than quartz. These other forms of silica include opal, chalcedony, flint and chert (non-crystalline), and cristobalite, tridymite, coesite, and stichovite. The latter four minerals are polymorphs of quartz, meaning that they have the same chemical composition (silica), but different crystalline forms (tetragonal or monoclinic). The various colors of chalcedony have their own names: jasper when brown, carnelian when red or reddish-brown, chrysoprase when green, agate when banded with different colors.

Sources

Quartz is found in many countries and many geologic environments. Major producers of natural quartz crystals are the United States (particularly Arkansas) and Brazil. Natural quartz is rarely used as found in nature (especially in electrical applications), except as a gemstone. Natural quartz crystals have too many chemical impurities and physical flaws. As a result, a commercial process of manufacturing pure, flawless, electronics-grade quartz was developed.

“Cultured quartz,” that is, quartz crystals grown very carefully in highly controlled laboratory conditions, is the quartz that is used in industry. About 200 metric tons of cultured quartz is produced each year.

In the production of cultured quartz crystals, a “seed crystal” is needed. A seed crystal is a small piece of carefully selected, non-electronics-grade quartz. The manufactured crystal grows on this seed crystal. Seed crystals of quartz are called lascas.

The United States is 100% dependent on imported lascas for manufactured quartz crystals. The major sources for lascas are Canada, Brazil, Germany and Madagascar. China, South Africa and Venezuela are other reported producers of quartz lascas.

Uses

caption Quartzite. (Source:Mineral Information Institute)

There are two entirely different major uses for quartz crystal. One of these is as a gemstone. The varieties known as rock crystal, amethyst, smoky quartz, rose quartz, and citrine are in demand as low-priced but attractive gemstone or display specimens. For gem applications, the quartz is usually cut and faceted for jewelry, or is carved into various shapes by hand or by laser.

Cultured quartz is used in electronic applications, where its special physical properties are valuable. Quartz is one of several minerals which are piezoelectric, meaning that when pressure is applied to quartz, a positive electrical charge is created at one end of the crystal and a negative electrical charge is created at the other. It is also strongly pyroelectric which means that temperature changes can cause the development of positive and negative charges within the crystal. These properties make quartz valuable in electronics applications. While some other minerals may have these properties, quartz is used because it is transparent, tough, and of unvarying chemical composition.

Electronics-grade manufactured quartz is used in a large number of circuits for consumer electronics products such as computers, cell phones, televisions, radios, and electronic games, to name just a few. It is also used to make frequency control devices and electronic filters that remove defined electromagnetic frequencies. In industry, quartz is also used in a variety of electronic devices.

Substitutes

Quartz is very abundant in the Earth’s crust so there is no danger of running short of easily available raw quartz for cultured quartz production. Even impure quartz can be purified and processed to create cultured quartz crystals. There is no adequate substitute for quartz in electronic applications. The only reason for insufficient quartz supplies would be if demand for cultured quartz outpaces industry’s ability to produce lascas and cultured quartz crystals.

Further Reading



Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Mineral Information Institute. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Mineral Information Institute should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

Glossary

Citation

Institute, M. (2008). Quartz. Retrieved from http://www.eoearth.org/view/article/155629

0 Comments

To add a comment, please Log In.