Quartz

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Quartz
Quartz Bresil.jpg
Quartz crystal cluster from Brazil
General
Category Silicate mineral [1]
Formula
(repeating unit)
SiO2
IMA symbol Qz [2]
Strunz classification 4.DA.05 (oxides)
Dana classification 75.01.03.01 (tectosilicates)
Crystal system α-quartz: trigonal
β-quartz: hexagonal
Crystal class α-quartz: trapezohedral (class 3 2)
β-quartz: trapezohedral (class 6 2 2) [3]
Space group α-quartz: P3221 (no. 154) [4]
β-quartz: P6222 (no. 180) or P6422 (no. 181) [5]
Unit cell a = 4.9133 Å, c = 5.4053 Å; Z = 3
Identification
Formula mass 60.083 g·mol−1
ColorColorless through various colors (pink, orange, purple, dark brown) to black
Crystal habit 6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive
Twinning Common Dauphine law, Brazil law, and Japan law
Cleavage {0110} Indistinct
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness7 – lower in impure varieties (defining mineral)
Luster Vitreous – waxy to dull when massive
Streak White
Diaphaneity Transparent to nearly opaque
Specific gravity 2.65; variable 2.59–2.63 in impure varieties
Optical properties Uniaxial (+)
Refractive index nω = 1.543–1.545
nε = 1.552–1.554
Birefringence +0.009 (B-G interval)
Pleochroism None
Melting point 1670 °C (β tridymite); 1713 °C (β cristobalite) [3]
Solubility Insoluble at STP; 1 ppmmass at 400 °C and 500  lb/in2 to 2600 ppmmass at 500 °C and 1500 lb/in2 [3]
Other characteristicsLattice: hexagonal, piezoelectric, may be triboluminescent, chiral (hence optically active if not racemic)
References [6] [7] [8] [9]

Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms 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 SiO2. 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. [10]

Contents

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 573 °C (846 K; 1,063 °F). 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 gemstones. Since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry 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 method for determining the hardness of a material to abrasion.

Etymology

The word "quartz" is derived from the German word Quarz, [11] which had the same form in the first half of the 14th century in Middle High German and in East Central German [12] and which came from the Polish dialect term kwardy, which corresponds to the Czech term tvrdý ("hard"). [13] Some sources, however, attribute the word's origin to the Saxon word Querkluftertz, meaning cross-vein ore. [14] [15]

The Ancient Greeks referred to quartz as κρύσταλλος (krustallos) derived from the Ancient Greek κρύος (kruos) meaning "icy cold", because some philosophers (including Theophrastus) understood the mineral to be a form of supercooled ice. [16] Today, the term rock crystal is sometimes used as an alternative name for transparent coarsely crystalline quartz. [17] [18]

Early studies

Roman naturalist Pliny the Elder believed quartz to be water ice, permanently frozen after great lengths of time. [19] He supported this idea by saying that quartz is found near glaciers in the Alps, but not on volcanic mountains, and that large quartz crystals were fashioned into spheres to cool the hands. This idea persisted until at least the 17th century. He also knew of the ability of quartz to split light into a spectrum. [20]

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. [21]

Crystal habit and structure

A-Quartz.svg
Crystal structure of α-quartz (red balls are oxygen, grey are silicon)
B-Quartz.svg
Crystal structure of β-quartz
Alpha-quartz, P3 121 and P3 221.png
A chiral pair of α-quartz

Quartz belongs to the trigonal crystal system at room temperature, and to the hexagonal crystal system above 573 °C (846 K; 1,063 °F). The ideal crystal shape is a six-sided prism terminating with six-sided pyramid-like rhombohedrons at each end. In nature, quartz crystals are often twinned (with twin right-handed and left-handed quartz crystals), distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive. [22] [23]

Well-formed crystals typically form as a druse (a layer of crystals lining a void), of which quartz geodes are particularly fine examples. [24] 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. [25]

α-quartz crystallizes in the trigonal crystal system, space group P3121 or P3221 (space group 152 or 154 resp.) depending on the chirality. Above 573 °C (846 K; 1,063 °F), 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). [26]

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. [22] [27] However, there is a significant change in volume during this transition,[ clarification needed ] and this can result in significant microfracturing in ceramics [28] and in rocks of the Earth's crust. [29]

Varieties (according to microstructure)

Although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. [30]

Major varieties of quartz
TypeColor and descriptionTransparency
Herkimer diamond ColorlessTransparent
Rock crystalColorlessTransparent
Amethyst Purple to violet colored quartzTransparent
Citrine Yellow quartz ranging to reddish-orange or brown (Madera quartz), and occasionally greenish yellowTransparent
Ametrine A mix of amethyst and citrine with hues of purple/violet and yellow or orange/brownTransparent
Rose quartz Pink, may display diasterism Transparent
Chalcedony Fibrous, variously translucent, cryptocrystalline quartz occurring in many varieties.
The term is often used for white, cloudy, or lightly colored material intergrown with moganite.
Otherwise more specific names are used.
Carnelian Reddish orange chalcedonyTranslucent
Aventurine Quartz with tiny aligned inclusions (usually mica) that shimmer with aventurescence Translucent to opaque
Agate Multi-colored, curved or concentric banded chalcedony (cf. Onyx)Semi-translucent to translucent
Onyx Multi-colored, straight banded chalcedony or chert (cf. Agate)Semi-translucent to opaque
Jasper Opaque cryptocrystalline quartz, typically red to brown but often used for other colorsOpaque
Milky quartz White, may display diasterism Translucent to opaque
Smoky quartz Light to dark gray, sometimes with a brownish hueTranslucent to opaque
Tiger's eye Fibrous gold, red-brown or bluish colored chalcedony, exhibiting chatoyancy.
Prasiolite GreenTransparent
Rutilated quartz Contains acicular (needle-like) inclusions of rutile
Dumortierite quartzContains large amounts of blue dumortierite crystalsTranslucent
PraseGreenTranslucent

Varieties (according to color)

Quartz crystal demonstrating transparency Transparency.jpg
Quartz crystal demonstrating transparency

Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent and has often been used for hardstone carvings, such as the Lothair Crystal. Common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. [31] These color differentiations arise from the presence of impurities which change the molecular orbitals, causing some electronic transitions to take place in the visible spectrum causing colors.

The most important distinction between types of quartz is that of macrocrystalline (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 transparent varieties tend to be macrocrystalline. Chalcedony is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. [32] Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, and jasper. [22]

Amethyst

Pure Quartz at Senckenberg Natural History Museum.jpg
Rock crystal
Amethyst Siberia MNHN Mineralogie.jpg
Amethyst
Shattuckite-Quartz-120842.jpg
Blue quartz
Dumortierite-quartz (Brazil) 10.jpg
Dumortierite quartz
Citrine 1 (Russie).jpg
Citrine quartz (natural)
Citrine Macro - Large Vug.jpg
Citrine quartz (heat-altered amethyst)
Quartz-221141.jpg
Milky quartz
Quartz-194084.jpg
Rose quartz
Quartz fume 2(Bresil).jpg
Smoky quartz
QuartzPrase.jpg
Prase

Amethyst is a form of quartz that ranges from a bright vivid violet to a dark or dull lavender shade. The world's largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, and Morocco. Sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine. Amethyst derives its color from traces of iron in its structure. [33]

Blue quartz

Blue quartz contains inclusions of fibrous magnesio-riebeckite or crocidolite. [34]

Dumortierite quartz

Inclusions of the mineral dumortierite within quartz pieces often result in silky-appearing splotches with a blue hue. Shades of purple or grey sometimes also are present. "Dumortierite quartz" (sometimes called "blue quartz") will sometimes feature contrasting light and dark color zones across the material. [35] [36] "Blue quartz" is a minor gemstone. [35] [37]

Citrine

Citrine is a variety of quartz whose color ranges from pale yellow to brown due to a submicroscopic distribution of colloidal ferric hydroxide impurities. [38] Natural citrines are rare; most commercial citrines are heat-treated amethysts or smoky quartzes. However, a heat-treated amethyst will have small lines in the crystal, as opposed to a natural citrine's cloudy or smoky appearance. 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". Sometimes citrine and amethyst can be found together in the same crystal, which is then referred to as ametrine. [39] Citrine has been referred to as the "merchant's stone" or "money stone", due to a superstition that it would bring prosperity. [40]

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. [41]

Milky quartz

Milk quartz or milky quartz is the most common variety of crystalline quartz. The white color is caused by minute fluid inclusions of gas, liquid, or both, trapped during crystal formation, [42] making it of little value for optical and quality gemstone applications. [43]

Rose quartz

Rose quartz is a type of quartz that exhibits a pale pink to rose red hue. The color is usually considered as due to trace amounts of titanium, iron, or manganese in the material. Some rose quartz contains microscopic rutile needles that produce asterism in transmitted light. Recent X-ray diffraction studies suggest that the color is due to thin microscopic fibers of possibly dumortierite within the quartz. [44]

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. [45] 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. [46]

Smoky quartz

Smoky quartz is a gray, translucent version of quartz. It ranges in clarity from almost complete transparency to a brownish-gray crystal that is almost opaque. Some can also be black. The translucency results from natural irradiation acting on minute traces of aluminum in the crystal structure. [47]

Prase

Prase is a green variety of quartz. [48] The green color is caused by inclusions of amphibole. [49]

Prasiolite

Prasiolite, also known as vermarine, is a variety of quartz that is green in color. [50] The green is caused by iron ions. [49] It is a rare mineral in nature and is typically found with amethyst; most "prasiolite" is not natural – it has been artificially produced by heating of amethyst. Since 1950[ citation needed ], almost all natural prasiolite has come from a small Brazilian mine, but it is also seen in Lower Silesia in Poland. Naturally occurring prasiolite is also found in the Thunder Bay area of Canada. [50]

Piezoelectricity

Quartz crystals have piezoelectric properties; they develop an electric potential upon the application of mechanical stress. [51] Quartz's piezoelectric properties were discovered by Jacques and Pierre Curie in 1880. [52] [53]

Occurrence

Quartz vein in sandstone, North Carolina Quartz vein in sandstone (Thunderhead Sandstone, Neoproterozoic; Clingmans Dome, Great Smoky Mountains, North Carolina, USA) 2 (36619574200).jpg
Quartz vein in sandstone, North Carolina

Quartz is a defining constituent of granite and other felsic igneous rocks. It is very common in sedimentary rocks such as sandstone and shale. It is a common constituent of schist, gneiss, quartzite and other metamorphic rocks. [22] Quartz has the lowest potential for weathering in the Goldich dissolution series and consequently it is very common as a residual mineral in stream sediments and residual soils. Generally a high presence of quartz suggests a "mature" rock, since it indicates the rock has been heavily reworked and quartz was the primary mineral that endured heavy weathering. [54]

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 pegmatites. [22] Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. [55]

The largest documented single crystal of quartz was found near Itapore, Goiaz, Brazil; it measured approximately 6.1 m × 1.5 m × 1.5 m and weighed 39,916 kilograms. [56]

Mining

Quartz is extracted from open pit mines. Miners occasionally use explosives to expose deep pockets of quartz. More frequently, bulldozers and backhoes are used to remove soil and clay and expose quartz veins, which are then worked using hand tools. Care must be taken to avoid sudden temperature changes that may damage the crystals. [57] [58]

Pressure-temperature diagram showing the stability ranges for the two forms of quartz and some other forms of silica P-T Diagram for SiO2.svg
Pressure-temperature diagram showing the stability ranges for the two forms of quartz and some other forms of silica

Tridymite and cristobalite are high-temperature polymorphs of SiO2 that occur in high-silica volcanic rocks. Coesite is a denser polymorph of SiO2 found in some meteorite impact sites and in metamorphic rocks formed at pressures greater than those typical of the Earth's crust. Stishovite is a yet denser and higher-pressure polymorph of SiO2 found in some meteorite impact sites. [60] Moganite is a monoclinic polymorph. Lechatelierite is an amorphous silica glass SiO2 which is formed by lightning strikes in quartz sand. [61]

Safety

As quartz is a form of silica, it is a possible cause for concern in various workplaces. Cutting, grinding, chipping, sanding, drilling, and polishing natural and manufactured stone products can release hazardous levels of very small, crystalline silica dust particles into the air that workers breathe. [62] Crystalline silica of respirable size is a recognized human carcinogen and may lead to other diseases of the lungs such as silicosis and pulmonary fibrosis. [63] [64]

Synthetic and artificial treatments

A synthetic quartz crystal grown by the hydrothermal method, about 19 centimetres (7.5 in) long and weighing about 127 grams (4.5 oz) Quartz synthese (cropped).jpg
A synthetic quartz crystal grown by the hydrothermal method, about 19 centimetres (7.5 in) long and weighing about 127 grams (4.5 oz)

Not all varieties of quartz are naturally occurring. Some clear quartz crystals can be treated using heat or gamma-irradiation to induce color where it would not otherwise have occurred naturally. Susceptibility to such treatments depends on the location from which the quartz was mined. [65]

Prasiolite, an olive colored material, is produced by heat treatment; [66] natural prasiolite has also been observed in Lower Silesia in Poland. [67] Although citrine occurs naturally, the majority is the result of heat-treating amethyst or smoky quartz. [66] Carnelian has been heat-treated to deepen its color since prehistoric times. [68]

Because natural quartz is often twinned, synthetic quartz is produced for use in industry. Large, flawless, single crystals are synthesized in an autoclave via the hydrothermal process. [69] [22] [70]

Like other crystals, quartz may be coated with metal vapors to give it an attractive sheen. [71] [72]

Uses

Quartz is the most common material identified as the mystical substance maban in Australian Aboriginal mythology. It is found regularly in passage tomb cemeteries in Europe in a burial context, such as Newgrange or Carrowmore in Ireland. Quartz was also used in Prehistoric Ireland, as well as many other countries, for stone tools; both vein quartz and rock crystal were knapped as part of the lithic technology of the prehistoric peoples. [73]

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 jewelry and hardstone carving, including engraved gems 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 cooker. [74] However, the quality and size of the crystals that were produced by these early efforts were poor. [75]

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. [76] A major mining location for high purity quartz is the Spruce Pine Gem Mine in Spruce Pine, North Carolina, United States. [77] Quartz may also be found in Caldoveiro Peak, in Asturias, Spain. [78]

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. [79] After the war, many laboratories attempted to grow large quartz crystals. In the United States, the U.S. Army Signal Corps contracted with Bell Laboratories and with the Brush Development Company of Cleveland, Ohio to synthesize crystals following Nacken's lead. [80] [81] (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. [82] [83] 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. [70]

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. [84] [85] George Washington Pierce designed and patented quartz crystal oscillators in 1923. [86] [87] [88] 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. [89] 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. [90]

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. [92] 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. [93]

See also

Related Research Articles

<span class="mw-page-title-main">Amethyst</span> Mineral, quartz variety

Amethyst is a violet variety of quartz. The name comes from the Koine Greek αμέθυστος amethystos from α-a-, "not" and μεθύσκωmethysko / μεθώmetho, "intoxicate", a reference to the belief that the stone protected its owner from drunkenness. Ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication.

<span class="mw-page-title-main">Agate</span> Rock consisting of cryptocrystalline silica alternating with microgranular quartz

Agate is the banded variety of chalcedony, which comes in a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks. The ornamental use of agate was common in Ancient Greece, in assorted jewelry and in the seal stones of Greek warriors, while bead necklaces with pierced and polished agate date back to the 3rd millennium BCE in the Indus Valley civilisation.

<span class="mw-page-title-main">Beryl</span> Gemstone: beryllium aluminium silicate

Beryl ( BERR-əl) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, pink, and red (the rarest). It is an ore source of beryllium.

<span class="mw-page-title-main">Gemstone</span> Piece of mineral crystal used to make jewelry

A gemstone is a piece of mineral crystal which, when cut or polished, is used to make jewelry or other adornments. Certain rocks and occasionally organic materials that are not minerals may also be used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some softer minerals such as brazilianite may be used in jewelry because of their color or luster or other physical properties that have aesthetic value. However, generally speaking, soft minerals are not typically used as gemstones by virtue of their brittleness and lack of durability.

<span class="mw-page-title-main">Mineral</span> Crystalline chemical element or compound formed by geologic processes

In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.

<span class="mw-page-title-main">Topaz</span> Silicate mineral

Topaz is a silicate mineral made of aluminum and fluorine with the chemical formula Al2SiO4(F, OH)2. It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can make it pale blue or golden brown to yellow-orange. Topaz is often treated with heat or radiation to make it a deep blue, reddish-orange, pale green, pink, or purple.

<span class="mw-page-title-main">Tourmaline</span> Cyclosilicate mineral group

Tourmaline is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors.

<span class="mw-page-title-main">Chalcedony</span> Microcrystalline varieties of silica

Chalcedony ( kal-SED-ə-nee, or KAL-sə-doh-nee) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic. Chalcedony's standard chemical structure (based on the chemical structure of quartz) is SiO2 (silicon dioxide).

<span class="mw-page-title-main">Opal</span> Hydrated amorphous form of silica

Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt.

<span class="mw-page-title-main">Smoky quartz</span> Mineral, quartz variety

Smoky quartz is a brownish grey, translucent variety of quartz that ranges in clarity from almost complete transparency to an almost-opaque brownish-gray or black crystals. The color of smoky quartz is produced when natural radiation, emitted from the surrounding rock, activates color centers around aluminum impurities within the crystalline quartz.

<span class="mw-page-title-main">Dioptase</span>

Dioptase is an intense emerald-green to bluish-green copper cyclosilicate mineral. It is transparent to translucent. Its luster is vitreous to sub-adamantine. Its formula is Cu6Si6O18·6H2O (also reported as CuSiO2(OH)2). It has a hardness of 5, the same as tooth enamel. Its specific gravity is 3.28–3.35, and it has two perfect and one very good cleavage directions. Additionally, dioptase is very fragile, and specimens must be handled with great care. It is a trigonal mineral, forming 6-sided crystals that are terminated by rhombohedra.

<span class="mw-page-title-main">Jadeite</span> Pyroxene mineral

Jadeite is a pyroxene mineral with composition NaAlSi2O6. It is hard (Mohs hardness of about 6.5 to 7.0), very tough, and dense, with a specific gravity of about 3.4. It is found in a wide range of colors, but is most often found in shades of green or white. Jadeite is formed only in the subduction zones of continental margins, where rock undergoes metamorphism at high pressure but relatively low temperature.

<span class="mw-page-title-main">Albite</span> Mineral, Na-feldspar, Na-silicate, tectosilicate

Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi
3
O
8
. It is a tectosilicate. Its color is usually pure white, hence its name from Latin, albus. It is a common constituent in felsic rocks.

<span class="mw-page-title-main">Chrysoprase</span> Gemstone variety of chalcedony

Chrysoprase, chrysophrase or chrysoprasus is a gemstone variety of chalcedony that contains small quantities of nickel. Its color is normally apple-green, but varies from turquoise-like cyan to deep green. The darker varieties of chrysoprase are also referred to as prase.

<span class="mw-page-title-main">Grossular</span> Garnet, nesosilicate mineral

Grossular is a calcium-aluminium species of the garnet group of minerals. It has the chemical formula of Ca3Al2(SiO4)3 but the calcium may, in part, be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from the botanical name for the gooseberry, grossularia, in reference to the green garnet of this composition that is found in Siberia. Other shades include cinnamon brown (cinnamon stone variety), red, and yellow. Grossular is a gemstone.

<span class="mw-page-title-main">Dumortierite</span>

Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, Al7BO3(SiO4)3O3. Dumortierite crystallizes in the orthorhombic system typically forming fibrous aggregates of slender prismatic crystals. The crystals are vitreous and vary in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium result in the color variations. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet. Dumortierite quartz is blue colored quartz containing abundant dumortierite inclusions.

<span class="mw-page-title-main">Painite</span> Borate mineral

Painite is a very rare borate mineral. It was first found in Myanmar by British mineralogist and gem dealer Arthur C.D. Pain who misidentified it as ruby, until it was discovered as a new gemstone in the 1950s. When it was confirmed as a new mineral species, the mineral was named after him. Due to its rarity, painite can cost between US$50,000 to $60,000 per carat.

<span class="mw-page-title-main">Ametrine</span> Mineral, quartz variety

Ametrine, also known as trystine or by its trade name as bolivianite, is a naturally occurring variety of quartz. It is a mixture of amethyst and citrine with zones of purple and yellow or orange. Almost all commercially available ametrine is mined in Bolivia.

<span class="mw-page-title-main">Prasiolite</span> Mineral, quartz variety

Prasiolite is a green variety of quartz.

<span class="mw-page-title-main">Jeremejevite</span>

Jeremejevite is an aluminium borate mineral with variable fluoride and hydroxide ions. Its chemical formula is Al6B5O15(F,OH)3. It is considered as one of the rarest, thus one of the most expensive stones. For nearly a century, it was considered as one of the rarest gemstones in the world.

References

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