Augen (from German "eyes") are large, lenticular eye-shaped mineral grains or mineral aggregates visible in some foliated metamorphic rocks . In cross section they have the shape of an eye.
63-398: Feldspar , quartz , and garnet are common minerals which form augen. Augen form in rocks which have undergone metamorphism and shearing . The core of the augen is a porphyroblast or porphyroclast of a hard, resilient mineral such as garnet. The augen grows by crystallisation of a mantle of new mineral around the porphyroblast. The mantle is formed contiguous with the foliation which
126-473: A druse (a layer of crystals lining a void), of which quartz geodes are particularly fine examples. 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 P 3 1 21 or P 3 2 21 (space group 152 or 154 resp.) depending on
189-560: A pressure cooker . However, the quality and size of the crystals that were produced by these early efforts were poor. 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
252-442: A Mars rock. Quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide ). The atoms are linked in a continuous framework of SiO 4 silicon–oxygen tetrahedra , with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO 2 . Quartz is, therefore, classified structurally as a framework silicate mineral and compositionally as an oxide mineral . Quartz
315-640: 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. 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
378-482: 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 . 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
441-511: A form of shear direction information. A metamorphic rock which is clotted with augen is often called an augen gneiss . A long wall of this augen gneiss can be felt at the Mineral and Lapidary Museum of Western North Carolina . This article related to petrology is a stub . You can help Misplaced Pages by expanding it . Feldspar Feldspar ( / ˈ f ɛ l ( d ) ˌ s p ɑːr / FEL(D) -spar ; sometimes spelled felspar )
504-584: 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. 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 . Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. The largest documented single crystal of quartz
567-435: A light microscope, whereas cryptoperthitic textures can be seen only with an electron microscope. Buddingtonite is an ammonium feldspar with the chemical formula: NH 4 AlSi 3 O 8 . It is a mineral associated with hydrothermal alteration of the primary feldspar minerals. Barium feldspars form as the result of the substitution of barium for potassium in the mineral structure. Barium feldspars are sometimes classified as
630-468: A mild abrasive action. The USGS estimated global production of feldspar in 2020 to be 26 million tonnes, with the top four producing countries being: China 2 million tonnes; India 5 million tonnes; Italy 4 million; Turkey 7.6 million tonnes. Typical mineralogical and chemical analyses of three commercial grades used in ceramics are: In October 2012, the Curiosity rover found high feldspar content in
693-399: A separate group of feldspars, and sometimes they are classified as a sub-group of alkali feldspars. The barium feldspars are monoclinic and include the following: The plagioclase feldspars are triclinic . The plagioclase series follows (with percent anorthite in parentheses): Intermediate compositions of exsolve to two feldspars of contrasting composition during cooling, but diffusion
SECTION 10
#1732851601971756-613: A short distance in cold and/or dry conditions that did not promote weathering, and that it was quickly buried by other sediment. Sandstones with large amounts of feldspar are called arkoses . Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as filler and an extender in paint, plastics, and rubber. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers and glass fibre. Ceramics (including electrical insulators, sanitaryware, tableware and tile) and other uses, such as fillers, accounted for
819-557: 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 . Quartz crystals have piezoelectric properties; they develop an electric potential upon the application of mechanical stress . Quartz's piezoelectric properties were discovered by Jacques and Pierre Curie in 1880. Quartz is
882-725: A source of alkalies and alumina in glazes. The composition of feldspar used in different ceramic formulations varies depending on various factors, including the properties of the individual grade, the other raw materials and the requirements of the finished products. However, typical additions include: tableware, 15% to 30% feldspar; high-tension electrical porcelains, 25% to 35%; sanitaryware, 25%; wall tile, 0% to 10%; and dental porcelain up to 80% feldspar. Earth sciences : In earth sciences and archaeology, feldspars are used for potassium-argon dating , argon-argon dating and luminescence dating . Minor use : Some household cleaners (such as Bar Keepers Friend and Bon Ami ) use feldspar to give
945-437: A submicroscopic distribution of colloidal ferric hydroxide impurities. 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
1008-669: 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. 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, making it of little value for optical and quality gemstone applications. Rose quartz
1071-476: A three-dimensional network. Compositions of major elements in common feldspars can be expressed in terms of three endmembers : Solid solutions between K-feldspar and albite are called alkali feldspar. Solid solutions between albite and anorthite are called plagioclase , or, more properly, plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two other solid solutions, immiscibility occurs at temperatures common in
1134-538: 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. Blue quartz contains inclusions of fibrous magnesio-riebeckite or crocidolite . Inclusions of
1197-700: Is a group of rock-forming aluminium tectosilicate minerals , also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust and 41% of the Earth's continental crust by weight. Feldspars crystallize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock . Rock formed almost entirely of calcic plagioclase feldspar
1260-419: Is a monoclinic polymorph. Lechatelierite is an amorphous silica glass SiO 2 which is formed by lightning strikes in quartz sand . 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
1323-456: Is a primary identifier for the macrocrystalline varieties. 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. These color differentiations arise from
SECTION 20
#17328516019711386-400: 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
1449-407: Is imparted upon the rock, and forms a blanket which tapers off from either side of the porphyroblast within the strain shadows. During shearing, the porphyroblast may rotate, to form a characteristic augen texture of asymmetric shearing. In this case, the position of the tails is unequal across the foliation, with some augen showing clear drag folding of the mantle into the strain shadow. This derives
1512-451: Is kinked. Each crankshaft chain links to neighbouring crankshaft chains to form a three-dimensional network of fused four-member rings. The structure is open enough for cations (typically sodium, potassium, or calcium) to fit into the structure and provide charge balance. Chemical weathering of feldspars happens by hydrolysis and produces clay minerals , including illite , smectite , and kaolinite . Hydrolysis of feldspars begins with
1575-660: Is known as anorthosite . Feldspars are also found in many types of sedimentary rocks . The name feldspar derives from the German Feldspat , a compound of the words Feld ("field") and Spat ("flake"). Spat had long been used as the word for "a rock easily cleaved into flakes"; Feldspat was introduced in the 18th century as a more specific term, referring perhaps to its common occurrence in rocks found in fields (Urban Brückmann, 1783) or to its occurrence as "fields" within granite and other minerals (René-Just Haüy, 1804). The change from Spat to -spar
1638-449: Is much slower than in alkali feldspar, and the resulting two-feldspar intergrowths typically are too fine-grained to be visible with optical microscopes. The immiscibility gaps in the plagioclase solid solutions are complex compared to the gap in the alkali feldspars. The play of colours visible in some feldspar of labradorite composition is due to very fine-grained exsolution lamellae known as Bøggild intergrowth. The specific gravity in
1701-514: Is often twinned , 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. 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
1764-702: Is the Spruce Pine Gem Mine 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
1827-471: 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 . Citrine has been referred to as the "merchant's stone" or "money stone", due to
1890-634: 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 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
1953-412: Is used for very accurate measurements of very small mass changes in the quartz crystal microbalance and in thin-film thickness monitors . 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
Augen - Misplaced Pages Continue
2016-524: 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 . Well-formed crystals typically form as
2079-843: The 14th century in Middle High German and in East Central German and which came from the Polish dialect term twardy , which corresponds to the Czech term tvrdý ("hard"). Some sources, however, attribute the word's origin to the Saxon word Querkluftertz , meaning cross-vein ore . 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
2142-602: The 1930s and 1940s. 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. (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,
2205-463: The Earth's crust means that clays are very abundant weathering products. About 40% of minerals in sedimentary rocks are clays and clays are the dominant minerals in the most common sedimentary rocks, mudrocks . They are also an important component of soils . Feldspar that has been replaced by clay looks chalky compared to more crystalline and glassy unweathered feldspar grains. Feldspars, especially plagioclase feldspars, are not very stable at
2268-405: The Earth's crust exposed to high temperatures, thereby damaging materials containing quartz and degrading their physical and mechanical properties. 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
2331-420: The Earth's surface due to their high formation temperature. This lack of stability is why feldspars are easily weathered to clays. Because of this tendency to weather easily, feldspars are usually not prevalent in sedimentary rocks. Sedimentary rocks that contain large amounts of feldspar indicate that the sediment did not undergo much chemical weathering before being buried. This means it was probably transported
2394-460: 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
2457-441: The air that workers breathe. 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 . 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
2520-464: The alkali feldspars occur only in higher temperature environments. Sanidine is stable at the highest temperatures, and microcline at the lowest. Perthite is a typical texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition. The perthitic textures in the alkali feldspars of many granites can be seen with the naked eye. Microperthitic textures in crystals are visible using
2583-407: 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
Augen - Misplaced Pages Continue
2646-444: The chirality. Above 573 °C (846 K; 1,063 °F), α-quartz in P 3 1 21 becomes the more symmetric hexagonal P 6 4 22 (space group 181), and α-quartz in P 3 2 21 goes to space group P 6 2 22 (no. 180). 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 (SiO 4 tetrahedra in
2709-443: The continuous Bowen's reaction series . K-feldspar is the final feldspar to crystallize from the magma. Alkali feldspars are grouped into two types: those containing potassium in combination with sodium, aluminium, or silicon; and those where potassium is replaced by barium. The first of these include: Potassium and sodium feldspars are not perfectly miscible in the melt at low temperatures, therefore intermediate compositions of
2772-470: The crust of the Earth. Albite is considered both a plagioclase and alkali feldspar. The ratio of alkali feldspar to plagioclase feldspar, together with the proportion of quartz , is the basis for the QAPF classification of igneous rock. Calcium-rich plagioclase is the first feldspar to crystallize from cooling magma, then the plagioclase becomes increasingly sodium-rich as crystallization continues. This defines
2835-466: The crystal structure. Prase is a green variety of quartz. The green color is caused by inclusions of amphibole . Prasiolite , also known as vermarine , is a variety of quartz that is green in color. The green is caused by iron ions. 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 , almost all natural prasiolite has come from
2898-433: The crystals. Tridymite and cristobalite are high-temperature polymorphs of SiO 2 that occur in high-silica volcanic rocks. Coesite is a denser polymorph of SiO 2 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 SiO 2 found in some meteorite impact sites. Moganite
2961-429: The feldspar dissolving in water, which happens best in acidic or basic solutions and less well in neutral ones. The speed at which feldspars are weathered is controlled by how quickly they are dissolved. Dissolved feldspar reacts with H or OH ions and precipitates clays. The reaction also produces new ions in solution, with the variety of ions controlled by the type of feldspar reacting. The abundance of feldspars in
3024-442: 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 . 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. Quartz belongs to the trigonal crystal system at room temperature, and to
3087-437: The impurities of phosphate and aluminium that formed crystalline rose quartz, unlike the iron and microscopic dumortierite fibers that formed rose 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
3150-452: The largest at that time. 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
3213-506: The location from which the quartz was mined. 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
SECTION 50
#17328516019713276-421: The mineral dumortierite within quartz pieces often result in silky-appearing splotches with a blue hue. Shades of purple or gray sometimes also are present. "Dumortierite quartz" (sometimes called "blue quartz") will sometimes feature contrasting light and dark color zones across the material. "Blue quartz" is a minor gemstone. Citrine is a variety of quartz whose color ranges from pale yellow to brown due to
3339-563: The mineral to be a form of supercooled ice. Today, the term rock crystal is sometimes used as an alternative name for transparent coarsely crystalline quartz. Roman naturalist Pliny the Elder believed quartz to be water ice , permanently frozen after great lengths of time. 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
3402-493: 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. The word "quartz" is derived from the German word Quarz , which had the same form in the first half of
3465-488: The plagioclase series increases from albite (2.62) to anorthite (2.72–2.75). The structure of a feldspar crystal is based on aluminosilicate tetrahedra. Each tetrahedron consists of an aluminium or silicon ion surrounded by four oxygen ions. Each oxygen ion, in turn, is shared by a neighbouring tetrahedron to form a three-dimensional network. The structure can be visualized as long chains of aluminosilicate tetrahedra, sometimes described as crankshaft chains because their shape
3528-494: 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
3591-403: 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
3654-504: The quartz. 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
3717-487: The remainder. Glass : Feldspar provides both K 2 O and Na 2 O for fluxing, and Al 2 O 3 and CaO as stabilizers. As an important source of Al 2 O 3 for glassmaking, feldspar is valued for its low iron and refractory mineral content, a low cost per unit of Al 2 O 3 , no volatiles and no waste. Ceramics : Feldspars are used in the ceramic industry as a flux to form a glassy phase in bodies during firing, and thus promote vitrification. They also are used as
3780-414: 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 . 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 . Amethyst
3843-420: Was first developed by Walter Guyton Cady in 1921. George Washington Pierce designed and patented quartz crystal oscillators in 1923. 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
SECTION 60
#17328516019713906-541: Was found near Itapore , Goiaz , Brazil; it measured approximately 6.1 m × 1.5 m × 1.5 m (20 ft × 5 ft × 5 ft) and weighed over 39,900 kg (88,000 lb). 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
3969-590: Was influenced by the English word spar , meaning a non-opaque mineral with good cleavage. Feldspathic refers to materials that contain feldspar. The alternate spelling, felspar , has fallen out of use. The term 'felsic', meaning light coloured minerals such as quartz and feldspars, is an acronymic word derived from fel dspar and si lica, unrelated to the obsolete spelling 'felspar'. The feldspar group of minerals consists of tectosilicates , silicate minerals in which silicon ions are linked by shared oxygen ions to form
#970029