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42-447: The Cians flows through the following communes: This river runs through a canyon of red shale , named " Gorges du Cians ", with formations of eroded rock. This Alpes-Maritimes geographical article is a stub . You can help Misplaced Pages by expanding it . This article related to a river in France is a stub . You can help Misplaced Pages by expanding it . Shale Shale is

84-426: A fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g., kaolin , Al 2 Si 2 O 5 ( OH ) 4 ) and tiny fragments ( silt -sized particles) of other minerals, especially quartz and calcite . Shale is characterized by its tendency to split into thin layers ( laminae ) less than one centimeter in thickness. This property

126-414: A hard, fissile, metamorphic rock known as slate . With continued increase in metamorphic grade the sequence is phyllite , then schist and finally gneiss . Shale is the most common source rock for hydrocarbons ( natural gas and petroleum ). The lack of coarse sediments in most shale beds reflects the absence of strong currents in the waters of the depositional basin. These might have oxygenated

168-435: 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

210-468: 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

252-399: 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

294-613: 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

336-725: 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

378-476: 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

420-1201: Is accompanied by telogenesis , the third and final stage of diagenesis. As erosion reduces the depth of burial, renewed exposure to meteoric water produces additional changes to the shale, such as dissolution of some of the cement to produce secondary porosity . Pyrite may be oxidized to produce gypsum . Black shales are dark, as a result of being especially rich in unoxidized carbon . Common in some Paleozoic and Mesozoic strata , black shales were deposited in anoxic , reducing environments, such as in stagnant water columns. Some black shales contain abundant heavy metals such as molybdenum , uranium , vanadium , and zinc . The enriched values are of controversial origin, having been alternatively attributed to input from hydrothermal fluids during or after sedimentation or to slow accumulation from sea water over long periods of sedimentation. Fossils , animal tracks or burrows and even raindrop impressions are sometimes preserved on shale bedding surfaces. Shales may also contain concretions consisting of pyrite, apatite , or various carbonate minerals. Shales that are subject to heat and pressure of metamorphism alter into

462-422: Is called fissility . Shale is the most common sedimentary rock. The term shale is sometimes applied more broadly, as essentially a synonym for mudrock , rather than in the narrower sense of clay-rich fissile mudrock. Shale typically exhibits varying degrees of fissility. Because of the parallel orientation of clay mineral flakes in shale, it breaks into thin layers, often splintery and usually parallel to

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504-638: Is composed of about 58% clay minerals, 28% quartz, 6% feldspar , 5% carbonate minerals, and 2% iron oxides . Most of the quartz is detrital (part of the original sediments that formed the shale) rather than authigenic (crystallized within the shale after deposition). Shales and other mudrocks contain roughly 95 percent of the organic matter in all sedimentary rocks. However, this amounts to less than one percent by mass in an average shale. Black shales, which form in anoxic conditions, contain reduced free carbon along with ferrous iron (Fe ) and sulfur (S ). Amorphous iron sulfide , along with carbon, produce

546-430: Is evidence that shale acts as a semipermeable medium, allowing water to pass through while retaining dissolved salts. The fine particles that compose shale can remain suspended in water long after the larger particles of sand have been deposited. As a result, shales are typically deposited in very slow moving water and are often found in lakes and lagoonal deposits, in river deltas , on floodplains and offshore below

588-451: 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

630-660: 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

672-455: Is more likely to form nonfissile mudstone than shale. On the other hand, black shales often have very pronounced fissility ( paper shales ) due to binding of hydrocarbon molecules to the faces of the clay particles, which weakens the binding between particles. Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. Pressure solution contributes to cementing, as

714-449: 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

756-452: Is reduced. In addition to this physical compaction, chemical compaction may take place via pressure solution . Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. It is during compaction that shale develops its fissility, likely through mechanical compaction of

798-399: The U.S. Gulf Coast . As sediments continue to accumulate, the older, more deeply buried sediments begin to undergo diagenesis . This mostly consists of compaction and lithification of the clay and silt particles. Early stages of diagenesis, described as eogenesis , take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in

840-651: The wave base . Thick deposits of shale are found near ancient continental margins and foreland basins . Some of the most widespread shale formations were deposited by epicontinental seas . Black shales are common in Cretaceous strata on the margins of the Atlantic Ocean , where they were deposited in fault -bounded silled basins associated with the opening of the Atlantic during the breakup of Pangaea . These basins were anoxic, in part because of restricted circulation in

882-511: 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

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924-420: 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

966-464: 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

1008-421: The black coloration. Because amorphous iron sulfide gradually converts to pyrite , which is not an important pigment, young shales may be quite dark from their iron sulfide content, in spite of a modest carbon content (less than 1%), while a black color in an ancient shale indicates a high carbon content. Most shales are marine in origin, and the groundwater in shale formations is often highly saline . There

1050-506: The clumps of clay particles produced by flocculation vary in size from a few tens of microns to over 700 microns in diameter. The floccules start out water-rich, but much of the water is expelled from the floccules as the clay minerals bind more tightly together over time (a process called syneresis ). Clay pelletization by organisms that filter feed is important where flocculation is inhibited. Filter feeders produce an estimated 12 metric tons of clay pellets per square kilometer per year along

1092-408: The color of the rock. Red, brown and green colors are indicative of ferric oxide ( hematite – reds), iron hydroxide ( goethite – browns and limonite – yellow), or micaceous minerals ( chlorite , biotite and illite – greens). The color shifts from reddish to greenish as iron in the oxidized ( ferric ) state is converted to iron in the reduced ( ferrous ) state. Black shale results from

1134-536: The context of underground coal mining , shale was frequently referred to as slate well into the 20th century. Black shale associated with coal seams is called black metal. [REDACTED] Media related to Shale at Wikimedia Commons Feldspar Feldspar ( / ˈ f ɛ l ( d ) ˌ s p ɑːr / FEL(D) -spar ; sometimes spelled felspar ) 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

1176-443: 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

1218-470: 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

1260-429: 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

1302-482: 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

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1344-592: The mineral dissolved from strained contact points is redeposited in the unstrained pore spaces. The clay minerals may be altered as well. For example, smectite is altered to illite at temperatures of about 55 to 200 °C (130 to 390 °F), releasing water in the process. Other alteration reactions include the alteration of smectite to chlorite and of kaolinite to illite at temperatures between 120 and 150 °C (250 and 300 °F). Because of these reactions, illite composes 80% of Precambrian shales, versus about 25% of young shales. Unroofing of buried shale

1386-433: The narrow Atlantic, and in part because the very warm Cretaceous seas lacked the circulation of cold bottom water that oxygenates the deep oceans today. Most clay must be deposited as aggregates and floccules, since the settling rate of individual clay particles is extremely slow. Flocculation is very rapid once the clay encounters highly saline sea water. Whereas individual clay particles are less than 4 microns in size,

1428-415: The original open framework of clay particles. The particles become strongly oriented into parallel layers that give the shale its distinctive fabric. Fissility likely develops early in the compaction process, at relatively shallow depth, since fissility does not seem to vary with depth in thick formations. Kaolinite flakes have less tendency to align in parallel layers than other clays, so kaolinite-rich clay

1470-505: The otherwise indistinguishable bedding planes . Non-fissile rocks of similar composition and particle size (less than 0.0625 mm) are described as mudstones (1/3 to 2/3 silt particles) or claystones (less than 1/3 silt). Rocks with similar particle sizes but with less clay (greater than 2/3 silt) and therefore grittier are siltstones . Shales are typically gray in color and are composed of clay minerals and quartz grains. The addition of variable amounts of minor constituents alters

1512-488: 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

1554-817: The presence of greater than one percent carbonaceous material and indicates a reducing environment. Pale blue to blue-green shales typically are rich in carbonate minerals . Clays are the major constituent of shales and other mudrocks. The clay minerals represented are largely kaolinite , montmorillonite and illite. Clay minerals of Late Tertiary mudstones are expandable smectites , whereas in older rocks (especially in mid-to early Paleozoic shales) illites predominate. The transformation of smectite to illite produces silica , sodium , calcium , magnesium , iron and water. These released elements form authigenic quartz , chert , calcite , dolomite , ankerite , hematite and albite , all trace to minor (except quartz) minerals found in shales and other mudrocks. A typical shale

1596-487: 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

1638-444: The richest source rocks may contain as much as 40% organic matter. The organic matter in shale is converted over time from the original proteins, polysaccharides , lipids , and other organic molecules to kerogen , which at the higher temperatures found at greater depths of burial is further converted to graphite and petroleum. Before the mid-19th century, the terms slate , shale and schist were not sharply distinguished. In

1680-433: The sediments, with only slight compaction. Pyrite may be formed in anoxic mud at this stage of diagenesis. Deeper burial is accompanied by mesogenesis , during which most of the compaction and lithification takes place. As the sediments come under increasing pressure from overlying sediments, sediment grains move into more compact arrangements, ductile grains (such as clay mineral grains) are deformed, and pore space

1722-414: The waters and destroyed organic matter before it could accumulate. The absence of carbonate rock in shale beds reflects the absence of organisms that might have secreted carbonate skeletons, also likely due to an anoxic environment. As a result, about 95% of organic matter in sedimentary rocks is found in shales and other mudrocks. Individual shale beds typically have an organic matter content of about 1%, but

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1764-590: 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

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