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Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom are linked in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of Silicon dioxide. Quartz is, therefore, classified structurally as a framework silicate mineral and compositionally as an oxide mineral. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.
Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral. The transformation from α-quartz to β-quartz takes place abruptly at . Since the transformation is accompanied by a significant change in volume, it can easily induce microfracturing of ceramics or rocks passing through this temperature threshold.
There are many different varieties of quartz, several of which are classified as . Since antiquity, varieties of quartz have been the most commonly used minerals in the making of Jewellery and hardstone carvings, especially in Europe and Asia.
Quartz is the mineral defining the value of 7 on the Mohs scale of hardness, a qualitative Scratch hardness method for determining the hardness of a material to abrasion.
The Ancient Greece referred to quartz as κρύσταλλος () derived from the Ancient Greek κρύος () meaning "icy cold", because some (including Theophrastus) understood the mineral to be a form of Supercooling ice. Today, the term Crystal is sometimes used as an alternative name for transparent coarsely crystalline quartz. (2025). 9780195106916, Oxford University Press. ISBN 9780195106916
In the 17th century, Nicolas Steno's study of quartz paved the way for modern crystallography. He discovered that regardless of a quartz crystal's size or shape, its long prism faces always joined at a perfect 60° angle, thus discovering the law of constancy of interfacial angles.Nicolaus Steno (Latinized name of Niels Steensen) with John Garrett Winter, trans., The Prodromus of Nicolaus Steno's Dissertation Concerning a Solid Body Enclosed by Process of Nature Within a Solid (New York, New York: Macmillan Co., 1916). On page 272 , Steno states his law of constancy of interfacial angles: "Figures 5 and 6 belong to the class of those which I could present in countless numbers to prove that in the plane of the axis both the number and the length of the sides are changed in various ways without changing the angles; … "
Well-formed crystals typically form as a druse (a layer of crystals lining a void), of which quartz are particularly fine examples. (1964). 9780442276249, Van Nostrand. ISBN 9780442276249 The crystals are attached at one end to the enclosing rock, and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, for instance, within gypsum.
α-quartz crystallizes in the trigonal crystal system, space group P3121 or P3221 (space group 152 or 154 resp.) depending on the chirality. Above , α-quartz in P3121 becomes the more symmetric hexagonal P6422 (space group 181), and α-quartz in P3221 goes to space group P6222 (no. 180).Crystal Data, Determinative Tables, ACA Monograph No. 5, American Crystallographic Association, 1963
These space groups are truly chiral (they each belong to the 11 enantiomorphous pairs). Both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks (SiO4 tetrahedra in the present case). The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, without a change in the way they are linked. However, there is a significant change in volume during this transition, and this can result in significant microfracturing in ceramics during firing, in ornamental stone after a fire and in rocks of the Earth's crust exposed to high temperatures, thereby damaging materials containing quartz and degrading their physical and mechanical properties.
The most important microstructure difference between types of quartz is that of macrocrystalline quartz (individual crystals visible to the unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification). The cryptocrystalline varieties are either translucent or mostly opaque, while the macrocrystalline varieties tend to be more transparent. Chalcedony is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Agate is a variety of chalcedony that is fibrous and distinctly banded with either concentric or horizontal bands. While most agates are translucent, onyx is a variety of agate that is more opaque, featuring monochromatic bands that are typically black and white. Carnelian or sard is a red-orange, translucent variety of chalcedony. Jasper is an opaque chert or impure chalcedony.
| + Varieties of quartz | |
| Transparent | Macrocrystalline |
| Transparent | Macrocrystalline |
| Transparent | Macrocrystalline |
| Transparent | Macrocrystalline |
| Translucent to opaque | Cryptocrystalline |
| Translucent | Cryptocrystalline |
| Translucent to opaque | Macrocrystalline |
| Semi-translucent to translucent | Cryptocrystalline |
| Semi-translucent to opaque | Cryptocrystalline |
| Opaque | Cryptocrystalline or Microcrystalline |
| Translucent to opaque | Macrocrystalline |
| Translucent to opaque | Macrocrystalline |
| Opaque | Cryptocrystalline |
| Transparent | Macrocrystalline |
| Transparent to translucent | Macrocrystalline |
| Translucent | Macrocrystalline |
Natural citrine is rare; most commercial citrine is heat-treated amethyst or smoky quartz. Amethyst loses its natural violet color when heated to above 200-300°C and turns a color that resembles natural citrine, but is often more brownish. Unlike natural citrine, the color of heat-treated amethyst comes from trace amounts of the iron oxide minerals hematite and goethite. Clear quartz with natural iron inclusions or limonite staining may also resemble citrine, but it is not true citrine. Like amethyst, heat-treated amethyst often exhibits color zoning, or uneven color distribution throughout the crystal. In geodes and clusters, the color is usually deepest near the tips. This does not occur in natural citrine.
It is nearly impossible to differentiate between cut citrine and yellow topaz visually, but they differ in hardness. Brazil is the leading producer of citrine, with much of its production coming from the state of Rio Grande do Sul. The name is derived from the Latin word citrina which means "yellow" and is also the origin of the word "citron". Citrine . Mindat.org (2013-03-01). Retrieved 2013-03-07. Citrine has been referred to as the "merchant's stone" or "money stone", due to a superstition that it would bring prosperity.
Citrine was first appreciated as a golden-yellow gemstone in Greece between 300 and 150 BC, during the Hellenistic Age. Yellow quartz was used prior to that to decorate jewelry and tools but it was not highly sought after.
Additionally, there is a rare type of pink quartz (also frequently called crystalline rose quartz) with color that is thought to be caused by trace amounts of phosphate or aluminium. The color in crystals is apparently photosensitive and subject to fading. The first crystals were found in a pegmatite found near Rumford, Maine, US, and in Minas Gerais, Brazil. The crystals found are more transparent and euhedral, due to the impurities of phosphate and aluminium that formed crystalline rose quartz, unlike the iron and microscopic dumortierite fibers that formed rose quartz.
While the majority of quartz crystallizes from molten magma, quartz also chemically precipitates from hot hydrothermal veins as gangue, sometimes with ore minerals like gold, silver and copper. Large crystals of quartz are found in magmatic . Well-formed crystals may reach several meters in length and mass hundreds of kilograms.
The largest documented single crystal of quartz was found near Itapore, Goyaz, Brazil; it measured approximately and weighed over .
Prasiolite, an olive colored material, is produced by heat treatment; natural prasiolite has also been observed in Lower Silesia in Poland. Although citrine occurs naturally, the majority is the result of heat-treating amethyst or smoky quartz. Carnelian has been heat-treated to deepen its color since prehistoric times.
Because natural quartz is often crystal twinning, synthetic quartz is produced for use in industry. Large, flawless, single crystals are synthesized in an autoclave via the hydrothermal process.
Like other crystals, quartz may be coated with metal vapors to give it an attractive sheen.Robert Webster, Michael O'Donoghue (2006). 9780750658560, Butterworth-Heinemann. . ISBN 9780750658560
While jade has been since earliest times the most prized semi-precious stone for carving in East Asia and Pre-Columbian America, in Europe and the Middle East the different varieties of quartz were the most commonly used for the various types of Jewellery and hardstone carving, including and cameo gems, rock crystal vases, and extravagant vessels. The tradition continued to produce objects that were very highly valued until the mid-19th century, when it largely fell from fashion except in jewelry. Cameo technique exploits the bands of color in onyx and other varieties.
Efforts to synthesize quartz began in the mid-nineteenth century as scientists attempted to create minerals under laboratory conditions that mimicked the conditions in which the minerals formed in nature: German geologist Karl Emil von Schafhäutl (1803–1890) was the first person to synthesize quartz when in 1845 he created microscopic quartz crystals in a Pressure cooking. From page 578: 5) Bildeten sich aus Wasser, in welchen ich im Papinianischen Topfe frisch gefällte Kieselsäure aufgelöst hatte, beym Verdampfen schon nach 8 Tagen Krystalle, die zwar mikroscopisch, aber sehr wohl erkenntlich aus sechseitigen Prismen mit derselben gewöhnlichen Pyramide bestanden. ( 5) There formed from water in which I had dissolved freshly precipitated silicic acid in a Papin pot i.e.,, after just 8 days of evaporating, crystals, which albeit were microscopic but consisted of very easily recognizable six-sided prisms with their usual pyramids.) However, the quality and size of the crystals that were produced by these early efforts were poor.Byrappa, K. and Yoshimura, Masahiro (2001) Handbook of Hydrothermal Technology. Norwich, New York: Noyes Publications. . Chapter 2: History of Hydrothermal Technology.
Elemental impurity incorporation strongly influences the ability to process and utilize quartz. Naturally occurring quartz crystals of extremely high purity, necessary for the crucibles and other equipment used for growing silicon wafers in the semiconductor industry, are expensive and rare. These high-purity quartz are defined as containing less than 50 ppm of impurity elements. A major mining location for high purity quartz is the Spruce Pine Mining District in Spruce Pine, North Carolina, United States. Quartz may also be found in Caldoveiro Peak, in Asturias, Spain.
By the 1930s, the electronics industry had become dependent on quartz crystals. The only source of suitable crystals was Brazil; however, World War II disrupted the supplies from Brazil, so nations attempted to synthesize quartz on a commercial scale. German mineralogist Richard Nacken (1884–1971) achieved some success during the 1930s and 1940s.Nacken, R. (1950) "Hydrothermal Synthese als Grundlage für Züchtung von Quarz-Kristallen" (Hydrothermal synthesis as a basis for the production of quartz crystals), Chemiker Zeitung, 74 : 745–749. After the war, many laboratories attempted to grow large quartz crystals. In the United States, the U.S. Army Signal Corps contracted with Bell Labs and with the Brush Development Company of Cleveland, Ohio to synthesize crystals following Nacken's lead. (Prior to World War II, Brush Development produced piezoelectric crystals for record players.) By 1948, Brush Development had grown crystals that were 1.5 inches (3.8 cm) in diameter, the largest at that time. "Record crystal", Popular Science, 154 (2) : 148 (February 1949).Brush Development's team of scientists included: Danforth R. Hale, Andrew R. Sobek, and Charles Baldwin Sawyer (1895–1964). The company's U.S. patents included:
By the 1950s, hydrothermal synthesis techniques were producing synthetic quartz crystals on an industrial scale, and today virtually all the quartz crystal used in the modern electronics industry is synthetic.
An early use of the piezoelectricity of quartz crystals was in phonograph pickups. One of the most common piezoelectric uses of quartz today is as a crystal oscillator. The quartz oscillator or resonator was first developed by Walter Guyton Cady in 1921. George Washington Pierce designed and patented quartz crystal oscillators in 1923.Pierce, George W. "Electrical system", , filed: 25 February 1924; issued: 18 October 1938. The quartz clock is a familiar device using the mineral. Warren Marrison created the first quartz oscillator clock based on the work of Cady and Pierce in 1927. The resonant frequency of a quartz crystal oscillator is changed by mechanically loading it, and this principle is used for very accurate measurements of very small mass changes in the quartz crystal microbalance and in thin-film thickness monitors. (NB. This was partially presented at Physikertagung in Heidelberg in October 1957.)
Almost all the industrial demand for quartz crystal (used primarily in electronics) is met with synthetic quartz produced by the hydrothermal process. However, synthetic crystals are less prized for use as gemstones. The popularity of crystal healing has increased the demand for natural quartz crystals, which are now often mined in developing countries using primitive mining methods, sometimes involving child labor.
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