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32-730: Charoite , a rare mineral, is found in the Murun Massif area of the plateau, rising between rivers Chara and Tokko . The Olyokma-Chara Plateau is located to the south of the Lena , at the southwestern end of the Sakha Republic in Olyokminsky District , and the eastern end of Irkutsk Oblast, Bodaybinsky District . The plateau is bound by the Chara River , a left tributary of the Olyokma river to

64-435: 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

96-468: 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

128-448: A pearly luster. Charoite is strictly massive in nature, and fractures are conchoidal . It has an unusual swirling, fibrous appearance, sometimes chatoyant , and that, along with its intense color, can lead many to believe at first that it is synthetic or enhanced artificially. Though reportedly discovered in the 1940s, it was not known to most of the world until its description in 1978. It is said to be opaque and unattractive when found in

160-399: 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

192-474: A shimmery looking polished stone. Sometimes, the very white flashes are tiny white feldspar. Sugilites and charoites can be confused, as both are purple, and sugilite can have black and white inclusions, however sugilite lacks the swirling pattern that are present in charoite stones, and it also lacks the chatoyant effect. It has been reported only from the Aldan Shield , Sakha Republic , Siberia, Russia. It

224-613: 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

256-725: 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

288-476: 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

320-509: Is a heat sensitive mineral, the mechanical cleaning of it should be avoided. It is recommended to use mild detergents and soft brushes or a cloth to clean it, and to never use strong and toxic detergents on it. 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

352-422: Is a rare silicate mineral with the chemical composition K(Ca,Na) 2 Si 4 O 10 (OH,F)•H 2 O , first described in 1978. It is named after the Chara River , despite its being 70 kilometres (43 mi) away from the discovery place. When it was discovered, it was thought to be a fake, dyed purple to give it its striking appearance. Charoite is translucent lavender to purple in color with

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384-456: Is a rock like lapis lazuli, but unlike the latter one, charoitite mostly consists of the mineral charoite. When it arrived to the western market, it was already named charoite. Common tradenames include charoite jade and lilac stone. Although considering its rarity and only type locality, even the highest quality charoite gemstones cost only a few dollars a carat, usually costing between 1.10 - $ 3 per carat. In its price, color and chatoyancy are

416-454: Is found where a syenite of the Murun Massif has intruded into and altered limestone deposits producing a potassium feldspar metasomatite , and forms between 200 - 250 °C. Tinaksite, canasite and charoite are associated and black aegirine is also common where these three minerals grow. Common impurities include aluminium , iron , manganese , strontium and barium . Charoitite

448-451: 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

480-660: 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

512-449: 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

544-511: 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

576-420: 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

608-464: 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

640-443: 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

672-470: 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

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704-429: 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

736-482: 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

768-420: The field; a fact that may have contributed to its late recognition. Charoite consists of oxygen (43.75%), silicon (27.65%) and calcium (17.53%) mainly, but its composition includes potassium (10.69%) - which gives it its radioactive properties - and hydrogen (0.39%) as well. It has a barely detectable, 0.65% radioactivity concentration per Gamma Ray American Petroleum Institute Units . Inclusions mainly come in

800-470: The main factors. Chatoyant translucent varieties are the most sought after, as while chatoyancy already being uncommon in the mineral, translucent varieties are rarer than the more common opaque ones. Alongside jewelry, due to the fact that the material can be massive in size, charoite can be used in the making of bookends, vases, goblets, boxes, or in small statues. Despite its relatively high hardness, it makes poor center pieces in rings and in bracelets. As it

832-488: 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

864-471: The plateau area. The heights of the Olyokma-Chara Plateau are moderate, the average elevations are between 500 meters (1,600 ft) and 600 meters (2,000 ft), although higher in the southern fringes. Mountains tend to be flat-topped, the highest point is Murun , a 1,452 metres (4,764 ft) high summit. The plateau is largely uninhabited. The settlement of Torgo , Olyokminsky District ,

896-487: 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

928-458: The swirly patterns of the mineral. The black spots on some specimens are either augite or aegirine , the latter occurring in almost all charoites since they commonly grow together. Larger round greenish spots are feldspar . Lighter colored stones or ones with translucent areas are likely due to canasite . The yellowish brown spots are tinaksite , which was discovered at the same time as charoite was. Charoite's silky, fibrous structure results in

960-963: The west and the Olyokma, a left tributary of the Lena, to the east. The Tokko River , the largest tributary of the Chara, crosses the uplands from south to north. To the south rises the Udokan Range of the Stanovoy Highlands and to the north the Lena Plateau . To the east rise the Aldan Highlands and to the west the Patom Highlands . The size of the plateau is roughly 180 kilometres (110 mi) from north to south, and 200 kilometres (120 mi) from east to west. There are vestiges of ancient glaciation throughout

992-593: Was abandoned in 2010. Part of the Olyokma-Chara Plateau falls within the Aldan Shield geological region. The plateau is composed of the Lower Paleozoic limestones in its northern part, and in the southern by Precambrian metamorphic shales , with granite intrusions . The mountains of the highlands are covered by larch taiga in the lower and middle slopes. Siberian pine scrub and mountain tundra grow at higher altitudes. Charoite Charoite ( / tʃ æ r oʊ . aɪ t / CHAR -ow-ait )

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1024-590: 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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