Difference between revisions of "Quartz" - New World Encyclopedia
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[[Image:QuartzUSGOV.jpg|left|thumb|Milk quartz.]] | [[Image:QuartzUSGOV.jpg|left|thumb|Milk quartz.]] | ||
| − | Given that natural quartz is often | + | Given that natural quartz is often twinned, much of the quartz used in industry is synthetically produced. Large, flawless, and untwinned crystals are produced in an autoclave via the [[hydrothermal]]* process. ([[Emerald]]s are also synthesized in this manner.) |
| − | Quartz occurs in [[Vein_(geology)|hydrothermal veins]] and [[pegmatite]]s. Well-formed crystals may reach several | + | Quartz occurs in [[Vein_(geology)|hydrothermal veins]] and [[pegmatite]]s. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. These veins may bear [[precious metals]]* such as [[gold]] or [[silver]], and form the quartz ores sought through [[mining]]. Erosion of pegmatites may reveal expansive pockets of crystals, known as "cathedrals." |
Quartz is a common constituent of [[granite]], [[sandstone]], [[limestone]], and many other [[igneous]], [[sedimentary]], and [[metamorphic rock|metamorphic]] rocks. | Quartz is a common constituent of [[granite]], [[sandstone]], [[limestone]], and many other [[igneous]], [[sedimentary]], and [[metamorphic rock|metamorphic]] rocks. | ||
| − | [[Tridymite]] and [[cristobalite]] are high temperature polymorphs of SiO<sub>2</sub> | + | [[Tridymite]]* and [[cristobalite]]* are high-temperature polymorphs of silica (SiO<sub>2</sub>), occurring in silica-rich volcanic rocks. [[Lechatelierite]]* is an [[amorphous]] silica [[glass]], which is formed by [[lightning]] strikes in quartz [[sand]]. |
==History== | ==History== | ||
| − | |||
| − | + | The name "quartz" comes from the German "Quarz," which is of Slavic origin (Czech miners called it křem). Some sources, however, trace the name to the Saxon word "Querkluftertz," meaning ''cross-vein ore''. | |
| − | + | Quartz is the most common material identified as the mystical substance "maban" in [[Australian Aboriginal mythology]]*. | |
| − | [[ | + | Roman naturalist [[Pliny the Elder]] believed quartz to be permanently frozen ice. In support of this idea, he said that quartz is found near glaciers in the Alps and that large quartz crystals were fashioned into spheres to cool the hands. He also knew of the ability of quartz to split light into a spectrum. |
| − | [[Charles Sawyer]] invented the commercial quartz crystal manufacturing process in [[Cleveland]], | + | Nicolas Steno's study of quartz paved the way for modern [[crystallography]]. He discovered that no matter how distorted a quartz crystal, the long prism faces always made a perfect 60-degree angle. |
| + | |||
| + | [[Charles Sawyer]]* invented the commercial quartz crystal manufacturing process in [[Cleveland]], [[Ohio]]. This process initiated the transition from mined to manufactured quartz. | ||
==Piezoelectricity== | ==Piezoelectricity== | ||
| − | + | ||
| + | A quartz crystal has a property known as ''piezoelectricity''—which means that when mechanical stress is put on the crystal, or when the crystal is made to vibrate, it produces electricity. One of the earliest uses for this property of quartz was in making the pickup for a [[phonograph]]*. | ||
| + | |||
| + | Today, one of the most ubiquitous piezoelectric uses of quartz is for "crystal oscillators," which are often simply called "quartzes." A quartz crystal oscillator is an [[electronic circuit]] in which the mechanical [[resonance]]* of a vibrating quartz crystal creates an electrical signal with a precise [[frequency]]*. This frequency is commonly used to keep track of time (as in [[quartz clock|quartz wristwatches]]*), to provide a stable clock signal for [[digital]]* [[integrated circuits]], and to stabilize frequencies for [[radio transmitter]]s. The crystal used therein is sometimes called a "timing crystal". | ||
| + | |||
| + | The piezoelectric principle is also used in the quartz crystal microbalance, which can make highly accurate measurements of tiny changes in mass. | ||
==See also== | ==See also== | ||
Revision as of 15:59, 1 June 2006
- For other uses, see Quartz (disambiguation).
| Quartz | |
|---|---|
| |
| General | |
| Category | Mineral |
| Chemical formula (or Composition) | Silica (silicon dioxide, SiO2) |
| Identification | |
| Color | Clear (if no impurities); also see Varieties |
| Crystal habit | 6-sided prism ending in 6-sided pyramid (typical) |
| Crystal system | Hexagonal |
| Cleavage | None |
| Fracture | Conchoidal |
| Mohs Scale hardness | 7 - lower in impure varieties |
| Luster | Vitreous/glossy |
| Refractive index | 1.544-1.553 - DR +0.009 (B-G interval) |
| Pleochroism | None |
| Streak | White |
| Specific gravity | 2.65 constant; variable in impure varieties |
| Melting point | 1650 (±75) °C |
| Boiling point | 2230 °C |
| Solubility | H2O insoluble |
| Major varieties | |
| Chalcedony | Any cryptocrystalline quartz, although generally only used for white or lightly coloured material. Otherwise more specific names are used. |
| Agate | Banded Chalcedony, translucent |
| Onyx | Agate where the bands are straight, parallel and consistent in size. |
| Jasper | Opaque chalcedony, impure |
| Aventurine | Translucent chalcedony with small inclusions (usually mica) that shimmer. |
| Tiger's eye | Fibrous quartz, exhibiting chatoyancy. |
| Rock Crystal | Clear, colourless |
| Ruby Quartz | Crimson glass-like crystal, absorbs vast amounts of solar energy |
| Amethyst | Purple, transparent |
| Citrine | Yellow to reddish orange, greenish yellow |
| Prasiolite | Mint green, transparent |
| Rose quartz | Pink, translucent, may display diasterism |
| Milk quartz, or snow quartz | White, translucent to opaque, may display diasterism |
| Smoky quartz | Brown, transparent |
| Morion | Dark-brown, opaque |
| Carnelian | Reddish orange chalcedony, translucent |
Quartz is one of the most common minerals in the Earth's continental crust. It has a hexagonal crystal structure made of trigonal crystallized silica (silicon dioxide, SiO2), with a hardness (resistance to scratching) of 7 on the Mohs scale of 1 to 10. Its density is 2.65 g/cm³. The typical shape of the crystal ("crystal habit") is a six-sided prism that ends in six-sided pyramids. The crystals, however, are often twinned, distorted, or so massive that only part of the shape is apparent from a mined specimen. Additionally, the crystals may take the form of a bed, particularly for varieties such as amethyst, in which the crystals grow up from a matrix and only one termination pyramid appears. A quartz geode consists of a hollow rock (usually with a roughly spherical shape) containing a core lined with a bed of crystals.
Varieties
Quartz is one of the world's most common crustal minerals and goes by a bewildering array of names. Some types of quartz have a "macrocrystalline" structure, in which individual crystals are visible to the unaided eye, while other types of quartz have a "microcrystalline" or "cryptocrystalline" structure, in which aggregates of crystals are visible only under high magnification. Chalcedony is a generic term for cryptocrystalline quartz. The cryptocrystalline varieties are translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline.
Although many of the varietal names historically arose from the mineral's color, current scientific naming schemes refer primarily to the mineral's microstructure. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. This does not always hold true.
Not all varieties of quartz are naturally occurring. Prasiolite, an olive colored material, is produced by heat treatment; natural prasiolite has also been obeserved in Lower Silesia in Poland. Although citrine occurs naturally, the majority is the result of heat-treated amethyst. Carnelian is widely heat-treated to deepen its color.
Given that natural quartz is often twinned, much of the quartz used in industry is synthetically produced. Large, flawless, and untwinned crystals are produced in an autoclave via the hydrothermal process. (Emeralds are also synthesized in this manner.)
Quartz occurs in hydrothermal veins and pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. These veins may bear precious metals such as gold or silver, and form the quartz ores sought through mining. Erosion of pegmatites may reveal expansive pockets of crystals, known as "cathedrals."
Quartz is a common constituent of granite, sandstone, limestone, and many other igneous, sedimentary, and metamorphic rocks.
Tridymite and cristobalite are high-temperature polymorphs of silica (SiO2), occurring in silica-rich volcanic rocks. Lechatelierite is an amorphous silica glass, which is formed by lightning strikes in quartz sand.
History
The name "quartz" comes from the German "Quarz," which is of Slavic origin (Czech miners called it křem). Some sources, however, trace the name to the Saxon word "Querkluftertz," meaning cross-vein ore.
Quartz is the most common material identified as the mystical substance "maban" in Australian Aboriginal mythology.
Roman naturalist Pliny the Elder believed quartz to be permanently frozen ice. In support of this idea, he said that quartz is found near glaciers in the Alps and that large quartz crystals were fashioned into spheres to cool the hands. He also knew of the ability of quartz to split light into a spectrum.
Nicolas Steno's study of quartz paved the way for modern crystallography. He discovered that no matter how distorted a quartz crystal, the long prism faces always made a perfect 60-degree angle.
Charles Sawyer invented the commercial quartz crystal manufacturing process in Cleveland, Ohio. This process initiated the transition from mined to manufactured quartz.
Piezoelectricity
A quartz crystal has a property known as piezoelectricity—which means that when mechanical stress is put on the crystal, or when the crystal is made to vibrate, it produces electricity. One of the earliest uses for this property of quartz was in making the pickup for a phonograph.
Today, one of the most ubiquitous piezoelectric uses of quartz is for "crystal oscillators," which are often simply called "quartzes." A quartz crystal oscillator is an electronic circuit in which the mechanical resonance of a vibrating quartz crystal creates an electrical signal with a precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters. The crystal used therein is sometimes called a "timing crystal".
The piezoelectric principle is also used in the quartz crystal microbalance, which can make highly accurate measurements of tiny changes in mass.
See also
- Fused quartz
- List of minerals
- Shocked quartz
ReferencesISBN links support NWE through referral fees
- Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0471805807
- Quartz group - Mineral Galleries
- Quartz - Mineral Galleries
- Quartz - Mineral.net
- Arkansas quartz, Rockhounding Arkansas
- Gilbert Hart Nomenclature of Silica, American Mineralogist, Volume 12, pages 383-395, 1927
- Mindat.org
- Queensland University of Technology Origin of the word quartz.
- PDF of Charles Sawyer's cultured quartz process description
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