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103-459: Micas are used in products such as drywalls , paints , and fillers, especially in parts for automobiles, roofing, and in electronics. The mineral is used in cosmetics and food to add "shimmer" or "frost". The mica group comprises 37 phyllosilicate minerals . All crystallize in the monoclinic system, with a tendency towards pseudohexagonal crystals , and are similar in structure but vary in chemical composition. Micas are translucent to opaque with

206-429: A discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of rock masses in, for example, tunnel , foundation , or slope construction. A hazard may exist even in undisturbed terrain. On August 17, 1959, a magnitude 7.2 earthquake destabilized a mountain slope near Hebgen Lake , Montana, composed of schist. This caused a massive landslide that killed 26 people camping in

309-553: A schistose metasandstone (if the protolith is known to have been a sandstone ). If all that is known is that the protolith was a sedimentary rock, the schist will be described as a paraschist , while if the protolith was an igneous rock, the schist will be described as an orthoschist . Mineral qualifiers are important when naming a schist. For example, a quartz-feldspar-biotite schist is a schist of uncertain protolith that contains biotite mica, feldspar , and quartz in order of apparent decreasing abundance. Lineated schist has

412-586: A better finish, the entire wall may be given a skim coat, a thin layer (about 1 mm or 1 ⁄ 32  in) of finishing compound, to minimize the visual differences between the paper and mudded areas after painting. Another similar skim coating process is called veneer plastering, although it is done slightly thicker (about 2 mm or 3 ⁄ 32  in). Veneering uses a slightly different specialized setting compound ("finish plaster") that contains gypsum and lime putty . This application uses blueboard, which has specially treated paper to accelerate

515-456: A commutator. The molding plate is also fabricated into tubes and rings for insulation in armatures, motor starters , and transformers. Segment plate acts as insulation between the copper commutator segments of direct-current universal motors and generators. Phlogopite built-up mica is preferred because it wears at the same rate as the copper segments. Although muscovite has a greater resistance to wear, it causes uneven ridges that may interfere with

618-426: A distinct vitreous or pearly luster, and different mica minerals display colors ranging from white to green or red to black. Deposits of mica tend to have a flaky or platy appearance. The crystal structure of mica is described as TOT-c , meaning that it is composed of parallel TOT layers weakly bonded to each other by cations ( c ). The TOT layers in turn consist of two tetrahedral sheets ( T ) strongly bonded to

721-873: A fluorine-rich mica, may replace natural ground mica for uses that require thermal and electrical properties of mica. Many materials can be substituted for mica in numerous electrical, electronic, and insulation uses. Substitutes include acrylate polymers , cellulose acetate , fiberglass , fishpaper , nylon , phenolics , polycarbonate , polyester , styrene , vinyl-PVC , and vulcanized fiber . Mica paper made from scrap mica can be substituted for sheet mica in electrical and insulation applications. [REDACTED]  This article incorporates public domain material from Mica . United States Geological Survey . Drywall Drywall (also called plasterboard , dry lining , wallboard , sheet rock , gib board , gypsum board , buster board , turtles board , slap board , custard board , gypsum panel and gyprock)

824-431: A hexagonal sheet. The remaining oxygen ion (the apical oxygen ion) is available to bond with the octahedral sheet. The octahedral sheet can be dioctahedral or trioctahedral. A trioctahedral sheet has the structure of a sheet of the mineral brucite , with magnesium or ferrous iron being the most common cation. A dioctahedral sheet has the structure and (typically) the composition of a gibbsite sheet, with aluminium being

927-409: A mica disc and contained in a borosilicate glass gas discharge tube (arc tube) and a metal cap. They include the sodium-vapor lamp that is the gas-discharge lamp in street lighting. Another use of mica is as a substrate in the production of ultra-flat, thin-film surfaces, e.g. gold surfaces. Although the deposited film surface is still rough due to deposition kinetics, the back side of the film at

1030-441: A mild abrasive to aid the polishing of the tooth surface and also adds a cosmetically pleasing, glittery shimmer to the paste. Mica is added to latex balloons to provide a colored shiny surface. Muscovite and phlogopite splittings can be fabricated into various built-up mica products, also known as micanite . Produced by mechanized or hand setting of overlapping splittings and alternate layers of binders and splittings, built-up mica

1133-416: A preferred direction in schist, often also forming very thin parallel layers. The ease with which the rock splits along the aligned grains accounts for the schistosity. Though not a defining characteristic, schists very often contain porphyroblasts (individual crystals of unusual size) of distinctive minerals, such as garnet , staurolite , kyanite , sillimanite , or cordierite . Because schists are

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1236-535: A reflective color depending on the thickness of the coating. These products are used to produce automobile paint, shimmery plastic containers, and high-quality inks used in advertising and security applications. In the cosmetics industry, its reflective and refractive properties make mica an important ingredient in blushes , eye liner , eye shadow , foundation , hair and body glitter, lipstick , lip gloss , mascara , moisturizing lotions, and nail polish. Some brands of toothpaste include powdered white mica. This acts as

1339-753: A second deposit was located in the Xalla Complex, another palatial structure east of Street of the Dead. There is a claim mica was found within the Pyramid of the Sun, which originates from Peter Tompkins in his book Mysteries of the Mexican Pyramids . But it is not yet proven. Natural mica was and still is used by the Taos and Picuris Pueblos Indians in north-central New Mexico to make pottery. The pottery

1442-412: A strong linear fabric in a rock which otherwise has well-developed schistosity. Schistosity is developed at elevated temperature when the rock is more strongly compressed in one direction than in other directions ( nonhydrostatic stress ). Nonhydrostatic stress is characteristic of regional metamorphism where mountain building is taking place (an orogenic belt ). The schistosity develops perpendicular to

1545-408: A very large class of metamorphic rock, geologists will formally describe a rock as a schist only when the original type of the rock prior to metamorphism (the protolith ) is unknown and its mineral content is not yet determined. Otherwise, the modifier schistose will be applied to a more precise type name, such as schistose semipelite (when the rock is known to contain moderate amounts of mica) or

1648-439: A week-long plaster application, an entire house can be drywalled in one or two days by two experienced drywallers , and drywall is easy enough to be installed by many amateur home carpenters. In large-scale commercial construction, the work of installing and finishing drywall is often split between drywall mechanics, or hangers , who install the wallboard, and tapers (also known as finishers, mud men , or float crew) who finish

1751-439: Is birefringent and is therefore commonly used to make quarter and half wave plates . Specialized applications for sheet mica are found in aerospace components in air-, ground-, and sea-launched missile systems, laser devices, medical electronics and radar systems. Mica is mechanically stable in micrometer-thin sheets which are relatively transparent to radiation (such as alpha particles ) while being impervious to most gases. It

1854-492: Is 48 inches; however, 54-inch-wide panels are becoming more popular as 9-foot (2.7 m) ceiling heights become more common. Lengths up to 16 feet (4.9 m) are common; the most common is 8 feet (2.4 m). Common thicknesses are 1 ⁄ 2 and 5 ⁄ 8 inch (13 and 16 mm); thicknesses of 1 ⁄ 4 ,  3 ⁄ 8 ,  3 ⁄ 4 , and 1 inch (6, 10, 19, and 25 mm) are used in specific applications. In many parts of Canada, drywall

1957-435: Is a panel made of calcium sulfate dihydrate ( gypsum ), with or without additives, typically extruded between thick sheets of facer and backer paper , used in the construction of interior walls and ceilings. The plaster is mixed with fiber (typically paper, glass wool , or a combination of these materials); plasticizer , foaming agent ; and additives that can reduce mildew , flammability , and water absorption. In

2060-505: Is an intermediate style step between full multi-coat "wet" plaster and the limited joint-treatment-only given "dry" wall. The method of installation and type of drywall can reduce sound transmission through walls and ceilings. Several builders' books state that thicker drywall reduces sound transmission, but engineering manuals recommend using multiple layers of drywall, sometimes of different thicknesses and glued together, or special types of drywall designed to reduce noise. Also important are

2163-556: Is called "FGD gypsum". This is commonly used in drywall construction in the United States and elsewhere. In 2020, 8.4 billion square meters of drywall were sold around the world. The term plasterboard is used in Australia and New Zealand . In Australia, the product is often called Gyprock , the name of the largest plasterboard manufacturer. In New Zealand it is also called Gibraltar and Gib board , genericised from

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2266-502: Is commonly made with one of three edge treatments: tapered edge, where the long edges of the board are tapered with a wide bevel at the front to allow jointing materials to be finished flush with the main board face; plain edge, used where the whole surface will receive a thin coating (skim coat) of finishing plaster; and beveled on all four sides, used in products specialized for roofing. Major UK manufacturers do not offer four-sided chamfered drywall for general use. As an alternative to

2369-557: Is commonly referred to as Gyproc. In Europe , most plasterboard is made in sheets 120 centimetres (47 in) wide; sheets 60 and 90 centimetres (24 and 35 in) wide are also made. Plasterboard 120 centimetres (47 in) wide is most commonly made in 240-centimetre (94 in) lengths; sheets of 250, 260, 270, 280, and 300 centimetres (98, 102, 106, 110, and 118 in) and longer also are common. Thicknesses of plasterboard available are 9.5 to 25 millimetres ( 3 ⁄ 8 to 1 in). Plasterboard

2472-631: Is cut to size by scoring the paper on the finished side (usually white) with a utility knife , breaking the sheet along the cut, and cutting the paper backing. Small features such as holes for outlets and light switches are usually cut using a keyhole saw , oscillating multi-tool or a tiny high-speed bit in a rotary tool. Drywall is then fixed to the structure with nails or drywall screws and often glue. Drywall fasteners , also referred to as drywall clips or stops , are gaining popularity in residential and commercial construction. Drywall fasteners are used for supporting interior drywall corners and replacing

2575-563: Is derived from the Latin word mica , meaning a crumb , and probably influenced by micare , to glitter. Human use of mica dates back to prehistoric times. Mica was known to ancient Indian , Egyptian , Greek , Roman , and Chinese civilizations, as well as the Aztec civilization of the New World . The earliest use of mica has been found in cave paintings created during

2678-522: Is discernible, the schist is usually given a name reflecting its protolith, such as schistose metasandstone . Otherwise, the names of the constituent minerals will be included in the rock name, such as quartz-felspar-biotite schist . Schist bedrock can pose a challenge for civil engineering because of its pronounced planes of weakness . The word schist is derived ultimately from the Greek word σχίζειν ( schízein ), meaning "to split", which refers to

2781-544: Is heated to drive off the water and then slightly rehydrated to produce the hemihydrate of calcium sulfate ( CaSO 4 · ⁠ 1 / 2 ⁠ H 2 O ). The plaster is mixed with fiber (typically paper and/or glass fiber ), plasticizer , foaming agent , finely ground gypsum crystal as an accelerator, EDTA , starch or other chelate as a retarder, and various additives that may increase mildew and fire resistance, lower water absorption ( wax emulsion or silanes ), reduce creep (tartaric or boric acid). The board

2884-536: Is made from weathered Precambrian mica schist and has flecks of mica throughout the vessels. Tewa Pueblo Pottery is made by coating the clay with mica to provide a dense, glittery micaceous finish over the entire object. Mica flakes (called abrak in Urdu and written as ابرک ) are also used in Pakistan to embellish women's summer clothes, especially dupattas (long light-weight scarves, often colorful and matching

2987-471: Is potential for using crushed drywall to amend certain soils at building sites, such as sodic clay and silt mixtures ( bay mud ), as well as using it in compost. As of 2016, industry standards are being developed to ensure that when and if wallboard is taken back for recycling, quality and composition are maintained. Schist Schist ( / ˈ ʃ ɪ s t / SHIST ) is a medium-grained metamorphic rock showing pronounced schistosity (named for

3090-461: Is produced all over the world. In 2010, the major producers were Russia (100,000 tonnes), Finland (68,000 t), the United States (53,000 t), South Korea (50,000 t), France (20,000 t) and Canada (15,000 t). The total global production was 350,000 t, although no reliable data were available for China. Most sheet mica was produced in India (3,500 t) and Russia (1,500 t). Flake mica comes from several sources:

3193-412: Is required. Organic dispersants and plasticizers are used so that the slurry will flow during manufacture and to reduce the water and hence the drying time. Coal-fired power stations include devices called scrubbers to remove sulfur from their exhaust emissions. The sulfur is absorbed by powdered limestone in a process called flue-gas desulfurization (FGD), which produces several new substances. One

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3296-476: Is resistant to corona discharge . Muscovite, the principal mica used by the electrical industry, is used in capacitors that are ideal for high frequency and radio frequency. Phlogopite mica remains stable at higher temperatures (to 900 °C (1,650 °F)) and is used in applications in which a combination of high-heat stability and electrical properties is required. Muscovite and phlogopite are used in sheet and ground forms. The leading use of dry-ground mica in

3399-447: Is stable when exposed to electricity, light, moisture, and extreme temperatures. It has superior electrical properties as an insulator and as a dielectric, and can support an electrostatic field while dissipating minimal energy in the form of heat; it can be split very thin (0.025 to 0.125 millimeters or thinner) while maintaining its electrical properties, has a high dielectric breakdown, is thermally stable to 500 °C (932 °F), and

3502-763: Is the name given to very fine, ragged grains and aggregates of white (colorless) micas. Mica is widely distributed and occurs in igneous , metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatites . The largest documented single crystal of mica ( phlogopite ) was found in Lacey Mine, Ontario , Canada ; it measured 10 m × 4.3 m × 4.3 m (33 ft × 14 ft × 14 ft) and weighed about 330 tonnes (320 long tons; 360 short tons). Similar-sized crystals were also found in Karelia , Russia . Scrap and flake mica

3605-482: Is the orientation of grains in the surrounding medium-grained rock. The composition of the rock must permit formation of abundant platy minerals. For example, the clay minerals in mudstone are metamorphosed to mica, producing a mica schist. Early stages of metamorphism convert mudstone to a very fine-grained metamorphic rock called slate , which with further metamorphism becomes fine-grained phyllite . Further recrystallization produces medium-grained mica schist. If

3708-417: Is then formed by sandwiching a core of the wet mixture between two sheets of heavy paper or fiberglass mats. When the core sets, it is dried in a large drying chamber, and the sandwich becomes rigid and strong enough for use as a building material . Drying chambers typically use natural gas today. To dry 1,000 square feet (93 m ) of wallboard, between 1,750,000 and 2,490,000 BTU (1.85–2.63 GJ)

3811-450: Is therefore used as a window on radiation detectors such as Geiger–Müller tubes . In 2008, mica splittings represented the largest part of the sheet mica industry in the United States. Consumption of muscovite and phlogopite splittings was about 308 t in 2008. Muscovite splittings from India accounted for essentially all US consumption. The remainder was primarily imported from Madagascar. Small squared pieces of sheet mica are also used in

3914-701: Is unable to be sold in the US. Some fire barrier walls are constructed of Type X drywall as a passive fire protection item. Gypsum contains the water of crystallization bound in the form of hydrates . When exposed to heat or fire , this water is vaporized, which retards heat transfer until the water in the gypsum is gone. The fire-resistance rating of the fire barrier assembly is increased with additional layers of drywall, up to four hours for walls and three hours for floor/ceiling assemblies. Fire-rated assemblies constructed of drywall are documented in design or certification listing catalogues, including DIN 4102 Part 4 and

4017-418: Is uncommon but can form from metamorphosis of sedimentary beds containing abundant organic carbon . This may be of algal origin. Graphite schist is known to have experienced greenschist facies metamorphism , for example in the northern Andes . Metamorphosis of felsic volcanic rock , such as tuff, can produce quartz- muscovite schist. In geotechnical engineering a schistosity plane often forms

4120-414: Is unusual in that it is a good electrical insulator at the same time as being a good thermal conductor. The leading use of block mica is as an electrical insulator in electronic equipment. High-quality block mica is processed to line the gauge glasses of high-pressure steam boilers because of its flexibility, transparency, and resistance to heat and chemical attack. Only high-quality muscovite film mica, which

4223-723: Is used in decorative coatings on wallpaper, concrete, stucco , and tile surfaces. It also is used as an ingredient in flux coatings on welding rods, in some special greases, and as coatings for core and mold release compounds, facing agents, and mold washes in foundry applications. Dry-ground phlogopite mica is used in automotive brake linings and clutch plates to reduce noise and vibration ( asbestos substitute); as sound-absorbing insulation for coatings and polymer systems; in reinforcing additives for polymers to increase strength and stiffness and to improve stability to heat, chemicals, and ultraviolet (UV) radiation; in heat shields and temperature insulation; in industrial coating additive to decrease

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4326-405: Is used in electric motor and generator armatures, field coil insulation, and magnet and commutator core insulation. Mica consumption in flexible plates was about 21 tonnes in 2008 in the US. A heater plate is used where high-temperature insulation is required. The molding plate is sheet mica from which V-rings are cut and stamped for use in insulating the copper segments from the steel shaft ends of

4429-625: Is used primarily as an electrical insulation material. Mica insulation is used in high-temperature and fire-resistant power cables in aluminium plants, blast furnaces , critical wiring circuits (for example, defence systems, fire and security alarm systems, and surveillance systems), heaters and boilers, lumber kilns , metal smelters, and tanks and furnace wiring. Specific high-temperature mica-insulated wire and cable are rated to work for up to 15 minutes in molten aluminium, glass, and steel. Major products are bonding materials; flexible, heater, molding, and segment plates; mica paper; and tape. Flexible plate

4532-608: Is variously called India ruby mica or ruby muscovite mica, is used as a dielectric in capacitors . The highest quality mica film is used to manufacture capacitors for calibration standards . The next lower grade is used in transmitting capacitors . Receiving capacitors use a slightly lower grade of high-quality muscovite. Mica sheets are used to provide structure for heating wire (such as in Kanthal or Nichrome ) in heating elements and can withstand up to 900 °C (1,650 °F). Single-ended self-starting lamps are insulated with

4635-444: Is wasted during the manufacturing and installation processes and the drywall material is frequently not reused, disposal can become a problem. Some landfill sites have banned the dumping of drywall. Some manufacturers take back waste wallboard from construction sites and recycle them into new wallboard. Recycled paper is typically used during manufacturing. More recently, recycling at the construction site itself has been researched. There

4738-634: The European Commission imposed fines totaling €420 million on the companies Lafarge , BPB , Knauf and Gyproc Benelux, which had operated a cartel on the market which affected 80% of consumers in France , the UK, Germany and the Benelux countries. A wallboard panel consists of a layer of gypsum plaster sandwiched between two layers of paper . The raw gypsum , CaSO 4 ·2H 2 O ,

4841-450: The Nara period . Yatsuomote ware is a type of local Japanese pottery from there. After an incident at Mount Yatsuomote a small bell was offered to soothe the kami . Katō Kumazō started a local tradition where small ceramic zodiac bells (きらら鈴) were made out of local mica kneaded into the clay , and after burning in the kiln the bell would make a pleasing sound when rung. Ayurveda ,

4944-409: The gypsum part of sheetrock are easily chewed out by honeybees when they are setting up a stray nest in a building, and they want to enlarge their nest area. A substantial amount of defective drywall was imported into the United States from China and incorporated into tens of thousands of homes during rebuilding in 2006 and 2007 following Hurricane Katrina and in other places. Complaints included

5047-486: The Canadian Building Code, Underwriters Laboratories and Underwriters Laboratories of Canada (ULC). Tests result in code-recognized designs with assigned fire-resistance ratings. The resulting designs become part of the code and are not limited to use by any manufacturer. However, individual manufacturers may also have proprietary designs that they have had third-party tested and approved, provided that

5150-462: The Hindu system of ancient medicine prevalent in India, includes the purification and processing of mica in preparing Abhraka bhasma, which is claimed as a treatment for diseases of the respiratory and digestive tracts. Mica dust in the workplace is regarded as a hazardous substance for respiratory exposure above certain concentrations. The Occupational Safety and Health Administration (OSHA) has set

5253-491: The US is in the joint compound for filling and finishing seams and blemishes in gypsum wallboard ( drywall ). The mica acts as a filler and extender, provides a smooth consistency, improves the workability of the compound, and provides resistance to cracking. In 2008, joint compounds accounted for 54% of dry-ground mica consumption. In the paint industry, ground mica is used as a pigment extender that also facilitates suspension, reduces chalking, prevents shrinking and shearing of

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5356-574: The Upper Paleolithic period (40,000 BC to 10,000 BC). The first hues were red ( iron oxide , hematite , or red ochre ) and black ( manganese dioxide , pyrolusite ), though black from juniper or pine carbons has also been discovered. White from kaolin or mica was used occasionally. A few kilometers northeast of Mexico City stands the ancient site of Teotihuacan . Mica was found in the noble palace complex "Viking Group" during an excavation led by Pedro Armillas between 1942 and 1944. Later,

5459-459: The affected drywall. They use rapid drying techniques that eliminate the elements required to support microbial activity while restoring most or all of the drywall. It is for these reasons that greenboard , a type of drywall with an outer face that is wax- and/or chemically coated to resist mold growth, and ideally cement board are used for rooms expected to have high humidity, primarily kitchens, bathrooms, and laundry rooms. Foam insulation and

5562-515: The apical sites vacant) or M 3 (OH) 2 (for a trioctahedral site with the apical sites vacant; M represents a divalent ion such as ferrous iron or magnesium) The combined TOT layer has a residual negative charge, since its bulk composition is Al 2 (AlSi 3 O 10 )(OH) 2 or M 3 (AlSi 3 O 10 )(OH) 2 . The remaining negative charge of the TOT layer is neutralized by the interlayer cations (typically sodium, potassium, or calcium ions). Because

5665-454: The beam and 400 to 600 mm across members. In both countries, plasterboard has become a widely used replacement for scrim and sarking walls in renovating 19th- and early 20th-century buildings. Drywall panels in Canada and the United States are made in widths of 48, 54, and 96 inches (1.2, 1.4, and 2.4 m) and varying lengths to suit the application. The most common width

5768-419: The best surface properties of any filled plastic composite. In 2008, consumption of dry-ground mica in plastic applications accounted for 2% of the market. The rubber industry used ground mica as an inert filler and mold release compound in the manufacture of molded rubber products such as tires and roofing. The platy texture acts as an anti-blocking, anti-sticking agent. Rubber mold lubricant accounted for 1.5% of

5871-458: The board—introduced during manufacturing to reduce the board's weight, lowering construction time and transportation costs—enables water to rapidly reach the core through capillary action , where mold can grow inside. Water that enters a room from overhead may cause ceiling drywall tape to separate from the ceiling as a result of the grooves immediately behind the tape where the drywall pieces meet becoming saturated. The drywall may also soften around

5974-491: The calcination of the gypsum in the core, allowing the core of the Type C panels to remain dimensionally stable in a fire. North America is one of the largest gypsum board users in the world, with a total wallboard plant capacity of 42 billion square feet (3.9 billion square metres) per year, roughly half of the worldwide annual production capacity of 85 billion square feet (7.9 billion square metres). Moreover,

6077-401: The cation. Apical oxygens take the place of some of the hydroxyl ions that would be present in a brucite or gibbsite sheet, bonding the tetrahedral sheets tightly to the octahedral sheet. Tetrahedral sheets have a strong negative charge since their bulk composition is AlSi 3 O 10 . The octahedral sheet has a positive charge, since its bulk composition is Al(OH) (for a dioctahedral sheet with

6180-428: The construction details of the framing with steel studs, wider stud spacing, double studding, insulation, and other details reducing sound transmission. Sound transmission class (STC) ratings can be increased from 33 for an ordinary stud-wall to as high as 59 with double 1 ⁄ 2 -inch (13 mm) drywall on both sides of a wood stud wall with resilient channels on one side and glass wool batt insulation between

6283-425: The conventional conical countersunk head; this compresses the drywall surface rather than cutting into it and so avoids tearing the paper. Screws for light-gauge steel framing have a sharp point and finely spaced threads. If the steel framing is heavier than 20- gauge , self-drilling screws with finely spaced threads must be used. In some applications, the drywall may be attached to the wall with adhesives . After

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6386-456: The direction of greatest compression, also called the shortening direction, as platy minerals are rotated or recrystallized into parallel layers. While platy or elongated minerals are most obviously reoriented, even quartz or calcite may take up preferred orientations. At the microscopic level, schistosity is divided into internal schistosity , in which inclusions within porphyroblasts take a preferred orientation, and external schistosity , which

6489-560: The dress). Thin mica flakes are added to a hot starch water solution, and the dupatta is dipped in this water mixture for 3–5 minutes. Then it is hung to air dry. Throughout the ages, fine powders of mica have been used for various purposes, including decorations. Powdered mica glitter is used to decorate traditional water clay pots in India, Pakistan and Bangladesh; it is also used on traditional Pueblo pottery, though not restricted to use on water pots in this case. The gulal and abir (colored powders) used by North Indian Hindus during

6592-434: The dry-ground mica used in 2008. As a rubber additive, mica reduces gas permeation and improves resiliency. Dry-ground mica is used in the production of rolled roofing and asphalt shingles , where it serves as a surface coating to prevent sticking of adjacent surfaces. The coating is not absorbed by freshly manufactured roofing because mica's platy structure is unaffected by the acid in asphalt or by weather conditions. Mica

6695-425: The ease with which schists can be split along the plane in which the platy minerals lie. Before the mid-19th century, the terms slate , shale and schist were not sharply differentiated by those involved with mining. Geologists define schist as medium-grained metamorphic rock that shows well-developed schistosity. Schistosity is a thin layering of the rock produced by metamorphism (a foliation ) that permits

6798-444: The elimination of the two inner layers of felt paper in favor of paper-based facings. In 1910 United States Gypsum Corporation bought Sackett Plaster Board Company and by 1917 introduced Sheetrock . Providing installation efficiency, it was developed additionally as a measure of fire resistance. Later air entrainment technology made boards lighter and less brittle, and joint treatment materials and systems also evolved. Gypsum lath

6901-490: The festive season of Holi contain fine crystals of mica to create a sparkling effect. The majestic Padmanabhapuram Palace , 65 km (40 mi) from Trivandrum in India, has colored mica windows. Mica powder is also used as a decoration in traditional Japanese woodblock printmaking , as when applied to wet ink with gelatin as thickener using kirazuri technique and allowed to dry, it sparkles and reflects light. Earlier examples are found among paper decorations, with

7004-450: The general formula in which Structurally, micas can be classed as dioctahedral ( Y = 4) and trioctahedral ( Y = 6). If the X ion is K or Na, the mica is a common mica, whereas if the X ion is Ca, the mica is classed as a brittle mica. Brittle micas: Common micas: Brittle micas: Very fine-grained micas, which typically show more variation in ion and water content, are informally termed "clay micas". They include: Sericite

7107-404: The gypsum panels resist fire without failure. Type C gypsum panels provide stronger fire resistance than Type X. The core of Type C panels contains a higher density of glass fibers. The core of Type C panels also contains vermiculite which acts as a shrinkage-compensating additive that expands when exposed to elevated temperatures of a fire. This expansion occurs at roughly the same temperature as

7210-483: The height as the Nishi Honganji 36 Poets Collection , codices of illuminated manuscripts in and after ACE 1112. For metallic glitter, Ukiyo-e prints employed very thick solution either with or without color pigments stencilled on hairpins, sword blades or fish scales on carp streamers ( 鯉のぼり , Koinobori ) . The soil around Nishio in central Japan is rich in mica deposits, which were already mined in

7313-425: The hexagons in the T and O sheets are slightly different in size, the sheets are slightly distorted when they bond into a TOT layer. This breaks the hexagonal symmetry and reduces it to monoclinic symmetry. However, the original hexahedral symmetry is discernible in the pseudohexagonal character of mica crystals. The short-range order of K ions on cleaved muscovite mica has been resolved. Chemically, micas can be given

7416-655: The highest quality. In Madagascar and India, it is also mined artisanally , in poor working conditions and with the help of child labour . The commercially important micas are muscovite and phlogopite , which are used in a variety of applications. Mica's value is based on its unique physical properties: the crystalline structure of mica forms layers that can be split or delaminated into thin sheets usually causing foliation in rocks. These sheets are chemically inert, dielectric , elastic, flexible, hydrophilic, insulating, lightweight, platy, reflective, refractive, resilient, and range in opacity from transparent to opaque. Mica

7519-829: The homebuilding and remodeling markets in North America in the late 1990s and early 2000s increased demand. The gypsum board market was one of the biggest beneficiaries of the housing boom as "an average new American home contains more than 7.31 metric tons of gypsum." The introduction in March 2005 of the Clean Air Interstate Rule by the United States Environmental Protection Agency requires fossil-fuel power plants to "cut sulfur dioxide emissions by 73%" by 2018. The Clean Air Interstate Rule also requested that

7622-436: The joints and cover the fastener heads with drywall compound . Drywall can be finished anywhere from a level 0 to a level 5, where 0 is not finished in any fashion, and five is the most pristine. Depending on how significant the finish is to the customer, the extra steps in the finish may or may not be necessary, though priming and painting of drywall are recommended in any location where it may be exposed to any wear. Drywall

7725-608: The legal limit ( permissible exposure limit ) for mica exposure in the workplace as 20 million parts per cubic foot (706,720,000 parts per cubic meter) over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 3 mg/m respiratory exposure over an 8-hour workday. At levels of 1,500 mg/m, mica is immediately dangerous to life and health . Some lightweight aggregates , such as diatomite , perlite , and vermiculite , may be substituted for ground mica when used as filler. Ground synthetic fluorophlogopite ,

7828-583: The loss of circulation by sealing porous sections of the drill hole. Well-drilling muds accounted for 15% of dry-ground mica use in 2008. The plastics industry used dry-ground mica as an extender and filler, especially in parts for automobiles as lightweight insulation to suppress sound and vibration. Mica is used in plastic automobiles fascia and fenders as a reinforcing material, providing improved mechanical properties and increased dimensional stability, stiffness, and strength. Mica-reinforced plastics also have high-heat dimensional stability, reduced warpage, and

7931-406: The material used in the field configuration can be demonstrated to meet the minimum requirements of Type X drywall and that sufficient layers and thicknesses are used. In the Type X gypsum board, special glass fibers are intermixed with the gypsum to reinforce the core of the panels. These fibers reduce the size of the cracks that form as the water is driven off, thereby extending the length of time

8034-446: The materials that constitute it: gypsum, paper, and organic additives and binders. Gypsum will soften with exposure to moisture and eventually turn into a gooey paste with prolonged immersion, such as during a flood. During such incidents, some, or all, of the drywall in an entire building will need to be removed and replaced. Furthermore, the paper facings and organic additives mixed with the gypsum core are food for mold. The porosity of

8137-468: The metamorphic rock called schist as a byproduct of processing feldspar and kaolin resources, from placer deposits, and pegmatites. Sheet mica is considerably less abundant than flake and scrap mica, and is occasionally recovered from mining scrap and flake mica. The most important sources of sheet mica are pegmatite deposits. Sheet mica prices vary with grade and can range from less than $ 1 per kilogram for low-quality mica to more than $ 2,000 per kilogram for

8240-527: The metamorphism proceeds further, the mica schist experiences dehydration reactions that convert platy minerals to granular minerals such as feldspars, decreasing schistosity and turning the rock into a gneiss. Other platy minerals found in schists include chlorite, talc, and graphite. Chlorite schist is typically formed by metamorphism of ultramafic igneous rocks, as is talc schist. Talc schist also forms from metamorphosis of talc-bearing carbonate rocks formed by hydrothermal alteration . Graphite schist

8343-669: The mica-film interface is ultra-flat once the film is removed from the substrate. Freshly-cleaved mica surfaces have been used as clean imaging substrates in atomic force microscopy , enabling for example the imaging of bismuth films, plasma glycoproteins , membrane bilayers , and DNA molecules. Thin transparent sheets of mica were used for peepholes in boilers, lanterns, stoves , and kerosene heaters because they were less likely to shatter than glass when exposed to extreme temperature gradients. Such peepholes were also fitted in horse-drawn carriages and early 20th-century cars, where they were called isinglass curtains . The word mica

8446-600: The mid-20th century, drywall construction became prevalent in North America as a time- and labor-saving alternative to lath and plaster . Sackett Board was invented in 1890 by New York Coal Tar Chemical Company employees Augustine Sackett and Fred L. Kane, graduates of Rensselaer Polytechnic Institute . It was made by layering plaster within four plies of wool felt paper. Sheets were 36 by 36 by 1 ⁄ 4 inch (914 mm × 914 mm × 6 mm) thick with open (untaped) edges. Gypsum board evolved between 1910 and 1930, beginning with wrapped board edges and

8549-426: The necessity of patching the damaged surface and repainting, if enough of the paper has been eaten, the gypsum core can easily crack or crumble without it, and the drywall must be removed and replaced. In many circumstances, especially when the drywall has been exposed to water or moisture for less than 48 hours, professional restoration experts can avoid the cost, inconvenience, and difficulty of removing and replacing

8652-417: The non-structural wood or metal blocking that traditionally was used to install drywall. Their function saves material and labor costs, minimizes call-backs due to truss uplift , increases energy efficiency , and makes plumbing and electrical installation simpler. When driven fully home, drywall screws countersink their heads slightly into the drywall. They use a 'bugle head', a concave taper, rather than

8755-532: The operation of a motor or generator. Consumption of segment plates was about 149 t in 2008 in the US. Some types of built-up mica have bonded splittings reinforced with cloth, glass, linen , muslin , plastic, silk, or special paper. These products are very flexible and are produced in wide, continuous sheets that are either shipped, rolled, or cut into ribbons or tapes, or trimmed to specified dimensions. Built-up mica products may also be corrugated or reinforced by multiple layering. In 2008, about 351 t of built-up mica

8858-510: The other two divisions being gneiss , which has poorly developed schistosity and thicker layering, and granofels , which has no discernible schistosity. Schists are defined by their texture without reference to their composition, and while most are a result of medium-grade metamorphism, they can vary greatly in mineral makeup. However, schistosity normally develops only when the rock contains abundant platy minerals, such as mica or chlorite . Grains of these minerals are strongly oriented in

8961-467: The paint film, increases the resistance of the paint film to water penetration and weathering and brightens the tone of colored pigments. Mica also promotes paint adhesion in aqueous and oleoresinous formulations. Consumption of dry-ground mica in paint, the second-ranked use, accounted for 22% of the dry-ground mica used in 2008. Ground mica is used in the well-drilling industry as an additive to drilling fluids . The coarsely ground mica flakes help prevent

9064-450: The permeability of moisture and hydrocarbons; and in polar polymer formulations to increase the strength of epoxies, nylons, and polyesters . Wet-ground mica, which retains the brilliance of its cleavage faces, is used primarily in pearlescent paints by the automotive industry. Many metallic-looking pigments are composed of a substrate of mica coated with another mineral, usually titanium dioxide (TiO 2 ). The resultant pigment produces

9167-480: The power plants install new scrubbers (industrial pollution control devices) to remove sulfur dioxide present in the output waste gas. Scrubbers use the technique of flue-gas desulfurization (FGD), which produces synthetic gypsum as a usable by-product. In response to the new supply of this raw material, the gypsum board market was predicted to shift significantly. However, issues such as mercury release during calcining need to be resolved. Because up to 12% of drywall

9270-400: The process of mountain building ( orogeny ) and usually reflects a medium grade of metamorphism. Schist can form from many different kinds of rocks, including sedimentary rocks such as mudstones and igneous rocks such as tuffs . Schist metamorphosed from mudstone is particularly common and is often very rich in mica (a mica schist ). Where the type of the original rock (the protolith )

9373-572: The registered trademark ("GIB") of the locally made product that dominates the local market. A specific type of Gibraltar board for use in wet conditions (such as bathrooms and kitchens) is known as AquaGib . It is made in thicknesses of 10 mm, 13 mm, and 16 mm, and sometimes other thicknesses up to 25 mm. Panels are commonly sold in 1200 mm-wide sheets, which may be 1800, 2400, 3000, 4800, or 6000 mm in length. Sheets are usually secured to either timber or cold-formed steel frames anywhere from 150 to 300 mm centres along

9476-424: The rock to easily be split into flakes or slabs less than 5 to 10 millimeters (0.2 to 0.4 in) thick. The mineral grains in a schist are typically from 0.25 to 2 millimeters (0.01 to 0.08 in) in size and so are easily seen with a 10× hand lens . Typically, over half the mineral grains in a schist show a preferred orientation. Schists make up one of the three divisions of metamorphic rock by texture , with

9579-457: The rock). This means that the rock is composed of mineral grains easily seen with a low-power hand lens , oriented in such a way that the rock is easily split into thin flakes or plates. This texture reflects a high content of platy minerals, such as mica , talc , chlorite , or graphite . These are often interleaved with more granular minerals, such as feldspar or quartz . Schist typically forms during regional metamorphism accompanying

9682-407: The screws holding the drywall in place, and with the aid of gravity, the weight of the water may cause the drywall to sag and eventually collapse, requiring replacement. Drywall's paper facings are edible to termites, which can eat the paper if they infest a wall cavity covered with drywall. This causes the painted surface to crumble to the touch, its paper backing material being eaten. In addition to

9785-427: The setting of the gypsum plaster component. This setting has far less shrinkage than the air-dry compounds normally used in drywall, so it only requires one coat. Blueboard also has square edges rather than tapered-edge drywall boards. The tapered drywall boards are used to countersink the tape in taped jointing, whereas the tape in veneer plastering is buried beneath a level surface. One coat veneer plaster over dry board

9888-416: The sheets are secured to the wall studs or ceiling joists , the installer conceals the seams between drywall sheets with joint tape or fiber mesh. Layers of joint compound, sometimes called mud, are typically spread with a drywall trowel or knife. This compound is also applied to any screw holes or defects. The compound is allowed to air dry and then typically sanded smooth before painting. Alternatively, for

9991-696: The sheets of drywall are simply marked "Made in China", thus making the manufacturer's identification difficult. An investigation by the Consumer Product Safety Commission , CPSC, was underway in 2009. In November 2009, the CPSC reported a "strong association" between Chinese drywall and corrosion of pipes and wires reported by thousands of homeowners in the United States. The issue was resolved in 2011, and now all drywall must be tested for volatile sulfur, and any containing more than ten ppm

10094-594: The structure's foul odour, health effects, and metal corrosion. The emission of sulfurous gases causes this. The same drywall was sold in Asia without problems resulting, but US homes are built much more tightly than homes in China, with less ventilation. Volatile sulfur compounds, including hydrogen sulfide , have been detected as emissions from the imported drywall and may be linked to health problems. These compounds are emitted from many different types of drywall. Several lawsuits are underway in many jurisdictions, but many of

10197-412: The studs. Sound transmission may be slightly reduced using regular 5 ⁄ 8 -inch (16 mm) panels (with or without light-gauge resilient metal channels and/or insulation), but it is more effective to use two layers of drywall, sometimes in combination with other factors, or specially designed, sound-resistant drywall. Drywall is highly vulnerable to moisture due to the inherent properties of

10300-573: The traditional Japanese Kōdō ceremony to burn incense: A burning piece of coal is placed inside a cone made of white ash. The sheet of mica is placed on top, acting as a separator between the heat source and the incense, to spread the fragrance without burning it. Sheet mica is used principally in the electronic and electrical industries. Its usefulness in these applications is derived from its unique electrical and thermal properties and its mechanical properties, which allow it to be cut, punched, stamped, and machined to close tolerances. Specifically, mica

10403-482: The two faces of a single octahedral sheet ( O ). The relatively weak ionic bonding between TOT layers gives mica its perfect basal cleavage. The tetrahedral sheets consist of silica tetrahedra, each silicon ion surrounded by four oxygen ions. In most micas, one in four silicon ions is replaced by an aluminium ion, while aluminium ions replace half the silicon ions in brittle micas. The tetrahedra share three of their four oxygen ions with neighbouring tetrahedra to produce

10506-442: Was an early substrate for plaster. An alternative to traditional wood or metal lath was a panel made up of compressed gypsum plaster board that was sometimes grooved or punched with holes to allow wet plaster to key into its surface. As it evolved, it was faced with paper impregnated with gypsum crystals that bonded with the applied facing layer of plaster. In 1936, US Gypsum trademarked ROCKLATH for their gypsum lath product. In 2002

10609-678: Was consumed in the US, mostly for molding plates (19%) and segment plates (42%). Sheet mica is a versatile and durable material widely used in electrical and thermal insulation applications. It exhibits excellent electrical properties, heat resistance, and chemical stability. Technical grade sheet mica is used in electrical components, electronics, atomic force microscopy and as window sheets. Other uses include diaphragms for oxygen-breathing equipment, marker dials for navigation compasses, optical filters , pyrometers , thermal regulators, stove and kerosene heater windows, radiation aperture covers for microwave ovens, and micathermic heater elements. Mica

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