Bowes, D. R., ed. The Encyclopedia of Igneous and Meta - morphic Petrology. New York: Van Nostrand Rein- hold, 1989. Bucher, Kurt, and Martin Frey. Petrogenesis of Metamor- phic Rocks.7th completelyrev.and updateded. New York: Springer, 2002. Philpotts, Anthony R., and Jay J. Ague. Principles of Ig- neous and Metamorphic Petrology. 2d ed. New York: Cambridge University Press, 2009. Raymond, Loren A. Petrology: The Study of Igneous, Sedi- mentary, and Metamorphic Rocks. 2d ed. Boston: McGraw-Hill, 2002. Winter, John D. An Introduction to Igneous and Metamor- phic Petrology. 2ded. NewYork: PrenticeHall, 2010. Web Site U.S. Geological Survey Metamorphic Rocks http://vulcan.wr.usgs.gov/LivingWith/ VolcanicPast/Notes/metamorphic_rocks.html See also: Asbestos; Corundum and emery; Garnet; Gneiss; Graphite; Kyanite; Marble; Mica; Plate tecton- ics; Slate; Talc. Methane Category: Mineral and other nonliving resources Where Found Methane is found throughout the crust of the Earth. The United States, Canada, and Russia have the larg- est output of natural gas from methane deposits. Methane is also found in mud volcanoes. The decom- position of landfill materials has resulted in the pro- duction of significant amounts of methane, and sev- eral landfill sites in the United States have been drilled into as a source. Primary Uses The main use of methane is as a fuel source. It also has several industrial uses. Technical Definition Methane isa naturallyoccurringgas composed of one atom of carbon and four atoms of hydrogen. This sta - ble chemical compound has the formula CH 4 and is classified as a hydrocarbon. Description, Distribution, and Forms Methane, a product of the decomposition of plant and animal remains, can be found throughout the Earth’s crust in varying amounts. Where it is found in greater concentrations, methane is the primary con- stituent innatural gas deposits,which are the target of oil and gas exploration efforts worldwide. Methane is also found in coal deposits as an integral part of the coalification process and can be recovered from wells drilled into the coal in the same manner in which oil and gas are obtained. History Methane was considered a waste by-product of oilpro- duction in the past, and trillions of cubic meters es- caped into the atmosphere in worldwide operations. Beginning in the 1950’s methane-based natural gas was seen as a viable energy source. Several interstate pipelines have been constructed in the United States, primarily to deliver the gas from its origins in the Gulf Coast and Midwest to the metropolitan areas of the Northeast. As late as the 1960’s, natural gas had little value in some areas, and wells drilled for oil that dis- covered natural gas instead were frequently aban- doned for lack of markets. Beginning in the 1980’s, methane was touted by some as the fuel of the future. It is clean burning, rel- atively inexpensive, and fairly easily transported throughout the United States. Its supply is forecast to continue for hundreds of years. Research has at- tempted to substitute methane-based natural gas as a motor fuel in cars, trucks, and locomotives, and many vehicles have been converted to use it. Its use as a mo- tor fuel will undoubtedly increase as more facilities are constructed to service existing and future vehi- cles. Obtaining Methane In spite of its advantages, methane has a significant disadvantage: It is explosive if mixed with air in a range of 5 percent to 15 percent by volume, and it has been blamed for several coal-mine disasters. As a re- sult, modern coal-mining practice removes as much methane from coal deposits as possible in advance of mining and maintains the methane-air mixture in the mining environment below 1 percent by volume. Since methane is not life-sustaining, its accumulation in underground coalmines canalso causea condition known as “firedamp,” which may asphyxiate mining personnel if undetected. 738 • Methane Global Resources Uses of Methane Methane is an excellent fuel for fuel cells. Fuel cells produce electricitydirectly from the interaction of hy- drocarbon and a catalyst. This interaction is not de- pendent on combustion but is a heat-producer,giving rise to the utilization of waste heat in various ways. It is expected that future fuel cell research, together with advances in the transportation sector, will place a greater demand on methane resources. Charles D. Haynes Web Site U.S. Environmental Protection Agency Methane http://www.epa.gov/methane/ See also: Fuel cells; Methanol; Oil and natural gas chemistry; Oil and natural gas reservoirs. Methanol Categories: Energy resources; products from resources Methanol is manufactured by the oxidation of natural gas or the reaction of carbon dioxide with hydrogen. It has numerous chemical uses and has potential as a partial replacement for gasoline. Background Methanol (also called methyl alcohol and wood alco- hol) is acolorless liquidwith little tasteor odor. Itboils at 64.51° Celsius and has a melting point (and triple point) of −97.56° Celsius. At 20° Celsius it has a vapor pressure of 97.60 torrs, a density of 0.7913 gram per milliliter, and an index of refraction of 1.3284. Its mo- lar mass is 32.04 grams. Methanol is completely solu- ble in water and most organic solvents. It has a flash point ofonly 11° Celsius and isthus highlyflammable. Methanol forms numerous binary and ternary azeo- tropic combinationswith avariety of compounds,so it is difficult to purify. Methanol is of considerable importance: It has long beenconsidered amajor industrialorganic chem- ical, andit has more recently beenidentified asa likely automotive fuel source. The world production capac - ity for methanol is more than 22 million metric tons per year. By 2013, worldwide consumption of metha - nol is estimated to reach 58 million metric tons, more than one-halfof which willbe consumedin China, the world’slargest producer andconsumer ofmethanol. Primary Uses A major portion of the methanol produced is used for the production of methyl esters such as methyl acrylate, methyl methacrylate, and methyl tere- phthalate, which are used in the manufacture of high- volume polymers. Methanol has been usedto prepare formaldehyde, but now more direct formaldehyde synthetic methods have somewhat reduced that us- age. Because formaldehyde is used in enormous quantities for production of synthetic water-based polymers, such as the phenolic and urea resins (em- ployed in plywood manufacture, for example), even the reduced formaldehyde production from metha- nol is important. A growing use for methanol is its reaction with isobutene (2-methylpropene) for the synthesis of methyl tertiary-butyl ether, a gasoline ad- ditive that is used in winter in many large cities to re- duce air pollution. Another group of major uses of methanol is for the chemical synthesis of acetic acid, methyl chloride, vinylacetate, vinylchloride, ethylene glycol (antifreeze), and other compounds. Methanol is also used as a solvent and extracting medium. Some methanol is used for the preparation of synthetic pro- tein. Methanol has an octane number value of 100; therefore, fueluses for methanolhave been proposed repeatedly. During the 1970’s, as petroleum prices skyrocketed, a number of processes for producing methanol for fuel purposes from wood or other bio- mass sources were considered. Vehicles capable of using methanol or a gasoline-methanol mix were de- veloped. As gas prices softened in the late 1990’s, automakers shifted attention to ethanol, which is more economical to produce, as methanol prices rose. Methanol continues to be used as a fuel for drag race cars, and it is widely used in China as an automo- bile fuel. Even though methanol combustion prod- ucts (almost entirely carbon dioxide and water) are nonpolluting and automobile engines can be easily modified to burn methanol, U.S. automakers have shifted their attention from methanol to hybrid and electric vehicles. Methanol Production Before 1930 the most common production method was the anaerobic destructive distillation of hard - Global Resources Methanol • 739 woods at temperatures below 400° Celsius. However, this method produced low yields (about 21 liters per metric ton of wood) of very impure methanol. Small amounts of relatively impure methanol produced in this manner are added to commercial ethanol to “de- nature” it andprevent thecommercialalcohol’s use as a beverage. Fermentation processes used to produce other alcoholshave not beensuccessful for methanol. However, because methanol is found in both plants and animals and is utilized by bacteria, fermentation appears to be a likely method if appropriate microor- ganisms could be identified or if genetically engi- neeredbacteria couldbe developedfor that purpose. The most often used synthetic processes involve re- actions of carbon monoxide and hydrogen (called synthesis gas),using catalysts such as copper, zinc,and chromium oxides at elevated pressures (above 300 at- mospheres) and at temperatures higher than 300° Celsius. The high-pressure process is sometimes re- placed with a lower-pressure one (below 100 atmo- spheres) at a somewhat lower temperature. The lower-pressure process requires more purified reac- tants and a more complex catalyst system but allows the reaction to proceed in simpler reactors. The syn- thesis gas is obtained by treating natural gas (meth- ane) or petroleumfractions withhigh-pressuresteam. Synthesis gas can also be obtained directly from coal, and if carbon dioxide is easily available, it may be more economicallydesirable to producethe synthesis gas from the prior reaction ofthe carbon dioxide with hydrogen. Toxicity Methanol, even in minute quanti- ties, is a powerful poison, acting on many parts of the nervous system, particularly the optic nerves. Blind- ness, at least temporary, often results from its ingestion. Methanol is oxi- dized in the body to formaldehyde and formic acid, which are the major direct culprits in methanol poison- ing. Coma and death frequently oc- cur as a result of methanol consump- tion. William J. Wasserman Further Reading Blume, David. Alcohol Can Be a Gas! Fueling an Ethanol Revolution for the Twenty-first Century. Santa Cruz, Calif.: Interna - tional Institute for Ecological Agriculture, 2007. Cheng, Wu-Hsun, and Harold H. Kung, eds. Methanol Production and Use. New York: M. Dekker, 1994. Kohl, Wilfrid L., ed. Methanol as an Alternative Fuel Choice: An Assessment. Washington, D.C.: Interna- tional Energy Program, Foreign Policy Institute, the Paul H. Nitze School of Advanced Interna- tional Studies, theJohns HopkinsUniversity,1990. Lee, Sunggyu. Methanol Synthesis Technology. Boca Raton, Fla.: CRC Press, 1990. Minteer, Shelley, ed. Alcoholic Fuels. Boca Raton, Fla.: CRC/Taylor & Francis, 2006. Mousdale, David M. Biofuels: Biotechnology, Chemistry, and Sustainable Development. Boca Raton, Fla.: CRC Press, 2008. Olah, George A., Alain Goeppert, and G. K. Surya Prakash. Beyond Oil and Gas: The Methanol Economy. Weinheim, Germany: Wiley, 2006. Paul, J. K., ed. Methanol Technology and Application in Motor Fuels. Park Ridge, N.J.: Noyes Data, 1978. Supp, Emil. How to Produce Methanol from Coal. New York: Springer, 1990. Web Site Alternative Fuels and Advanced Vehicles Data Center, U.S. Department of Energy Methanol http://www.afdc.energy.gov/afdc/fuels/ methanol.html 740 • Methanol Global Resources An Indy Racing League carrefuelswith methanol during a 2003 race.(GettyImages) See also: Biofuels; Biotechnology; Energy econom - ics; Ethanol; Methane; Petroleum refining and pro- cessing; Plant domestication and breeding; Synthetic Fuels Corporation; Wood and charcoal as fuel re- sources. Mexico Categories: Countries; government and resources Mexico is second in worldwide silver production; the metal has been mined in the region since 1546. One- seventh of the annual global production of silver comes from Mexico. Mexico is the sixth largest producer of pe- troleum worldwide. The crude oil industry accounts for one-third of the nation’s annual revenue and is controlled by a government-operated company. The Country Mexico is located in North America, sharing a border with the United States to the north. It is bordered to the south by Belize and Guatemala in Central Amer- ica. To the east, Mexico borders the Caribbean Sea and the Gulf of Mexico. The country’s western shore meets the Pacific Ocean, the Gulf of California, and the Gulf of Tehuantepec. Only about one-third of Mexico is flat. A chain of volcanic mountains runs east-west across the country just south of Mexico City. Plateaus also dominate the landscape. The Sierra Madre mountain chains surround the region’s pla- teau in a V shape. The Sonoran Desert covers the area east ofthe Gulf ofCalifornia. Mexico’s economy isthe eleventh largest in the world. In 2007, the average an- nual income was $14,400. A large portion of Mexico’s income results from oil production. The country is a leading producer of silver and also mines copper, lead, zinc, and gold. Silver Mexico is the second leading producer of silver in the world (2.8 million kilograms in 2007). Four of the top twelve silver mines (in terms of production) in 2007 were located inMexico’s silver beltin thecenter ofthe country. The majority of silver is taken from mines in Guanajuato, Pachuca, and Zacatecas. The cityof Taxco is oneof theoldest mining sites in the Western Hemisphere. Within a year of conquer - ing the Aztecs in 1521, the Spanish discovered the value of Taxco. By the beginning of the seventeenth century, silver mined in Taxco could be found throughout Europe. Taxco became known worldwide for its silver wealth. For the Spanish, it also was the pri- mary mining site for several precious metals. How- ever, as richer and more accessible veins were found, Taxco slowly faded in mining importance. Don Joséde laBorda, knownas thefather ofTaxco, rediscovered the city’s silver wealth in 1716. He used part of the fortune he made to build schools, houses, roads, and Taxco’s famous Santa Prisca Cathedral. Silversmithing and mining was forgotten again dur- ing Mexico’s war for independence. The Spanish de- stroyed the silver mines so that Mexican revolutionar- ies could not gain their control. William Spratling, an American professor of archi- tecture, moved to Mexico in 1929. Spratling became interested in Taxco’s silver history. He encouraged lo- cal artists to become silversmiths. Spratling also cre- ated an apprenticeship program for local silversmiths with promising artistic talent, training them using his own designs.Taxco againbecame world famous for its silver, this time primarily for the jewelry made from the metal.Silverware andjewelry aremade out ofster- ling silver, which is 92.5 percent silver and 7.5 percent copper. Jewelry is often coated with a thin layer of 0.999 fine silver to give it extra shine. Britannia silver is also usedfor utensilsand is 95.8percent pure silver. In the modern world economy, Taxco is the world leader in silver production. Numerous silver stores are located in and around the town’s main plaza. Taxco is home to both the Spratling Museum and the Silver Museum. In 1937, Spratling created the silver fair as a party for local artists working with silver. The fair has become a national event, involving Mexico’s finest silversmiths and some of the world’s best artists. In 1953, Mexico’s president created National Silver Day, which is celebrated the last Saturday of Novem- ber. The silver fair starts that Saturday and ends the first Sunday of December each year. Petroleum Petroleum and petroleum-related products have a long history in Mexico. Asphalt and bitumen, or pitch, has been used in Mexico since the time of the Aztecs. They are believed to have used asphalt to se- cure stone arrowheads on the ends of wooden spears. The first time oil was refined into kerosene was in 1876, near the city of Tampico on Mexico’s eastern coast. By1917, large quantitiesof Mexicanoil were be - Global Resources Mexico • 741 742 • Mexico Global Resources Mexico: Resources at a Glance Official name: United Mexican States Government: Federal republic Capital city: Mexico City Area: 758,505 mi 2 ; 1,964,375 km 2 Population (2009 est.): 111,211,789 Language: Spanish Monetary unit: Mexican peso (MXN) Economic summary: GDP composition by sector (2008 est.): agriculture, 3.8%; industry, 35.2%; services, 61% Natural resources: petroleum, silver, copper, gold, lead, zinc, natural gas, timber Land use (2005): arable land, 12.66%; permanent crops, 1.28%; other, 86.06% Industries: food and beverages, tobacco, chemicals, iron and steel, petroleum, mining, textiles, clothing, motor vehicles, consumer durables, tourism Agricultural products: corn, wheat, soybeans, rice, beans, cotton, coffee, fruit, tomatoes, beef, poultry, dairy products, wood products Exports (2008 est.): $291.3 billion Commodities exported: manufactured goods, oil and oil products, silver, fruits, vegetables, coffee, cotton Imports (2008 est.): $308.6 billion Commodities imported: metalworking machines, steel mill products, agricultural machinery, electrical equipment, car parts for assembly, repair parts for motor vehicles, aircraft, and aircraft parts Labor force (2008 est.): 45.32 million Labor force by occupation (2005): agriculture, 15.1%; industry, 25.7%; services, 59% Energy resources: Electricity production (2007 est.): 243.3 billion kWh Electricity consumption (2007 est.): 202 billion kWh Electricity exports (2007 est.): 1.278 billion kWh Electricity imports (2007 est.): 484.2 million kWh Natural gas production (2007 est.): 55.98 billion m 3 Natural gas consumption (2007 est.): 68.29 billion m 3 Natural gas exports (2007 est.): 2.973 billion m 3 Natural gas imports (2007 est.): 11.69 billion m 3 Natural gas proved reserves ( Jan. 2008 est.): 392.2 billion m 3 Oil production (2007 est.): 3.501 million bbl/day Oil imports (2005): 385,400 bbl/day Oil proved reserves ( Jan. 2008 est.): 13.68 billion bbl Source: Data from The World Factbook 2009. Washington, D.C.: Central Intelligence Agency, 2009. Notes: Data are the most recent tracked by the CIA. Values are given in U.S. dollars. Abbreviations: bbl/day = barrels per day; GDP = gross domestic product; km 2 = square kilometers; kWh = kilowatt-hours; m 3 = cubic meters; mi 2 = square miles. Mexico City Cuba Guatemala Belize Honduras United States Mexico Caribbean Sea Gulf of Mexico Pacific Ocean ing drilled and refined by American and British companies. The Mexican government then proclaimed in its con- stitution ownership of all the country’s mineral rights. In 1938, strikes over wages from foreign-owned companies led to the creation of Petroleos Mexi- canos (Pemex) by Mexican president Lázaro Cárdenas. This caused many of the foreign companies to leave Mex- ico. Pemex is the ninth largest oil com- pany worldwide, and the largest in Latin America. Pemex is responsible for exploration, extraction, refining, transportation, distribution, and mar- keting of petroleum, petroleum prod- ucts, and natural gas. Between heavy taxes and direct payments made to the government, Pemex is responsible for one-third of Mexico’s annualrevenues. Mexico is the world’s sixth largest producer of crude oil (3.5 million bar- rels per day in 2007) and is ninth in ex- ports. It ranks seventeenth by amount of oil reserves. However, Mexico has passed peak production of oil, deplet- ing its resources, and overall produc- tion has begun to decline. This could be a serious problem for the country because of how heavily the government relieson moneyfrom the petroleumin- dustry.In April, 2009, oil production in Mexico was 1.37 million barrels per day, a figure that was under the target for the year. By 2010, Mexico’s oil exports were expected to decline by 18 percent. Pemex has begun looking for new oil fields using seis- mic technology. Scientists senda seismicwave into the ground and can use computers to measure its reflec- tion, which tells about the structure underground. Geologists can use this information to help deter- mine the best places to drill for oil. Natural Gas Methane is the main component of natural gas. In ad- dition to methane, natural gas can include ethane, propane, butane, carbon dioxide, nitrogen, and he- lium. Natural gas, like petroleum and coal, forms from fossil fuels or in isolated natural gas fields. Ex - tensive refining removes almost everything but meth - ane. The natural gas industry in Mexico is run by Pemex. In 2008, Mexico ranked sixteenth in natural- gas production (55,980 million cubic meters) and thirty-fourth globally in proven reserves (392.2billion cubic meters). In 1995, some control of the natural gas industry was turned over to private industry. Pemex continued to control exploration, production, and firsthand sales. Pemex continues to own most of the pipelines throughout the country. Private companies handle transportation, storage, and distribution of natural gas. In 2005, several natural gas sites were found, which increased production and jobs. In 2007, natu- ral gas pipelines became the target of attacks by the Ejército Popular Revolucionario (the People’s Revo- lutionary Army), a small antigovernment terrorist group formed in the 1990’s. The attacks resulted in the loss of hundreds of millions of dollars in produc - tion profits. Global Resources Mexico • 743 In this 1952 photograph, a worker guides a rock crusher at the Real del Monte silver mine in Mexico. Mexico haslongbeena leader in silver production. (GettyImages) Copper In the late nineteenth century, a series of copper de- posits were found near Santa Rosalía. These mines have been mostly depleted. Remaining copper is pro- duced from open-pit mines near Cananea and La Caridad. Mexico remains the twenty-second largest exporter of copper in the world. In 2007, copper exports brought in more than $320 million for Mex- ico. The top copper-exporting nation is Chile, where the industry made $5 billion in 2007. There are insuf- ficient known reserves to maintain the world’s cur- rent consumption of copper. Scientists estimate that the world population will deplete the Earth of known copper by about 2070 if the current rate of consump- tion continues. However, if the demand continues to increase, the world’s copper might last until only 2035. Mexico’s largest mining company, Grupo Mexico SAB, has been fighting a lawsuit over control of the Southern Copper Corporation of Peru. American courts ruled that Grupo Mexico had to return 30 per- cent of its stock in Southern Copper to another min- ing company, Asarco. Asarco, a company based in Tucson, Arizona, was owned by Grupo Mexico until 2005, when it became board-managed, and the legal battle started. In 2009, Grupo Mexico appealed the judge’s ruling. At the same time, Grupo Mexico was dealing with a strike among its workers at the coun- try’s largest copper mine, Cananea, near the U.S. bor- der. The strike started over health and safety stan- dards. The company was given permission to fire fifteen hundred striking workers in 2009. Mexico’s la- bor board shut down the mine because idle machin- ery had been looted and damaged beyond repair. Grupo Mexico has worked to reopen the copper pit with plans to hire two thousand workers to make it operational. Zinc In 2006, Mexico was ranked sixth in global zinc pro- duction, producing 453,893 metric tons. Mexico ex- ported $172.8 million worth of zinc in 2007, ranking ninth worldwide. Canada is the world’s leading zinc exporter, making more than $546 million in 2007. The largest producer of zinc in Mexico is the state of Chihuahua. The Charcas mine in the state of San Luis Potosí, in north-central Mexico, is the top zinc- producing mine. Production of zinc in the country has risen; new mines were opened in 2001, and others expanded in 2002. A Canadian company, Canasil Re - sources, found a vein of zinc and silver in the state of Durango. The company was exploring a 29-square- kilometer patch of flatland with a geologic intrusion. Samples taken of the intrusion in 2006 were found to contain high levels of zinc. Canasil expanded its prop- erty in the area to include an addition 1,000 square kilometers to the north and east. Early stages of drill- ing began in 2007. Two zones containing high con- centrations of zinc at relatively shallow depths were found with the potential to yield a new zinc district in Mexico. Forests and Timber Scientists estimate that in the mid-sixteenth century more than two-thirds of Mexico was forest. Today, the tropical forests of the southern and eastern parts of the country are largely all that remain. However, Mex- ico contains 1.3 percent of the world’s total forest reserves, and one-quarter of the country is classified as forest. Mexico has more species of pine and oak trees than anywhere else in the world. Nonetheless, logging has depleted Mexico’s forests severely. Some pine forests in the northern part of the country have been conserved, but the practice is not widespread. The national tree is the cypress, which is found near water in semiarid regions. Mexico also has a number of ceiba trees, which were sacred to the Mayas. The Mayas believed that a ceiba tree stood at the center of the Earth, connecting it with the spirit world over- head. Ceiba trees grow in tropical regions, tall with large canopies that house several different species. Even in modern deforestation, ceiba trees are often spared. Mexico’s rain forests along the gulf coast and throughout the country are being cut down, and the land burned by farmers to expand their fields. This rain forest is part of the Maya Forest, which covers the Yucatán Peninsula, northern Guatemala, and parts of Belize, 5.3 million hectares in total. Efforts to pre- serve the forest, and the Mayan ruins within, have been complicated bya rapidly growing population. In addition to use as farmland, the forests are being cut down to make room for roads, dams, and other ac- commodations needed to handle an influx of workers and tourists to the region. In 1978, the Mexican gov- ernment set up an international sanctuary to protect 331,200 hectares of rain forest. However, the Montes Azules Biosphere Reserve continues to shrink each year. Support for the preservation of the reserve is worldwide: In 2004, the European Union pledged 31 744 • Mexico Global Resources million euros (approximately $44 million) for four years in an effort to aid the tribes that live in and near the sanctuary. Poverty and population growth have re- sulted in destruction of the forest. Many valuable types of wood are found in the tropi- cal forests, including hardwoods such as various oaks and mahogany. The forests also contain cedar and rosewood. Sapodilla trees are found in Mexico’s rain forests and are the basis of chicle. Chicle is a form of latex that is used in chewing gum. In 2000, Mexico’s forestry imports exceeded exports by $2.46 billion. However, many other products are found in the for- ests ofMexico, includinggums, resins,fibers, oils, and waxes. Other Resources Mexico is twenty-fourth in the world in exportation of nonmonetary gold. In 2007, gold exports amounted to more than $160 million. Gold is a popular metal used in jewelry, sculpture, and coins. Gold occurs nat- urally as granules, nuggets, and large deposits. Lead is another metal that is heavily mined in Mex- ico. Bullets, pipes, pewter, radiation shields, batteries, and weights are all made from lead. Lead is also poi- sonous and can cause a variety of problems, including blood and brain disorders, nerve damage, even death. Mexico is also the sixth largest producer of salt in the world. Jennifer L. Campbell Further Reading Bowles, Ian, and Glenn Prickett, eds. Footprints in the Jungle: Natural Resource Industries, Infrastructure, and Biodiversity Conservation. New York: Oxford Univer- sity Press, 2001. Fernandez, Linda, andRichard Carson, eds. Both Sides of the Border: Transboundary Environmental Manage- ment Issues Facing Mexico and the United States. New York: Springer, 2002. Ibarrarán, María, and Roy Boyd. Hacia el Futuro: En- ergy, Economics, and the Environment in Twenty-first Century Mexico. New York: Springer, 2006. Joseph, Gilbert, and Timothy Henderson, eds. The Mexican Reader: History, Culture, Politics. Durham, N.C.: Duke University Press, 2003. Meyer, Michael C., and William H. Beezley, eds. The Oxford History of Mexico. New York: Oxford Univer- sity Press, 2000. Nobel, John, ed. Mexico. 11th ed. Oakland, Calif.: Lonely Planet, 2008. Primack, Richard, et al., eds. Timber, Tourists, and Tem - ples: Conservation and Development in the Maya Forest of Belize, Guatemala, and Mexico. Washington, D.C.: Island Press, 1997. See also: Copper; Forests; Gold; Oil and natural gas reservoirs; Silver. Mica Category: Mineral and other nonliving resources Where Found Micas are common rock-forming minerals and are widely distributed throughout the world. They occur in igneous, metamorphic, and sedimentary rocks. They are mined as sheets or flakes and scrap. Sheet mica is primarily found in Brazil, Madagascar, India, and Canada. Muscovite flakes are mined in the United States from igneous pegmatites and metamor- phic schists located in North and South Carolina, Connecticut, Georgia, and New Mexico. Primary Uses Muscovite sheets are used as electrical insulators in the electronic and computer industries. Scrap mica is ground and used primarily as a coating material and in the paint industry. Technical Definition The mica group of minerals is composed mainly of muscovite, KAl 2 (AlSi 3 O 10 )(OH) 2 ; biotite, K(Mg,Fe) 3 (AlSi 3 O 10 )(OH) 2 ; phlogopite KMg 3 (AlSi 3 O 10 )(OH) 2 ; and lepidolite, K(Li,Al) 3 (AlSi 3 O 10 )(OH) 2 ; although there are thirty known mica minerals. Micas are hy- drous aluminum silicate minerals that have a perfect basal cleavage. Micas have a hardness of 2.5 to 4 and show a vitreous to pearly luster. Muscovite is a type of mica that is colorless and transparent in thin sheets and white to light brown or light yellow in thicker blocks. Phlogopite is yellow to brown with a copper- colored reflection off cleavage surfaces. Biotite is pri- marily black but can appear dark green or brown. Lepidolite has a distinctive lilac to pink color. Description, Distribution, and Forms Micas form monoclinic crystals that inevitably show a perfect basal cleavage. Crystals and their cleavage Global Resources Mica • 745 sheets commonly display a hexagonal form. Musco- vite and biotite can be found in thick “books” contain- ing layer uponlayer of thin cleavagesheets, which can be up to 3 meters across in pegmatites. Micas are common throughout the world. Musco- vite is characteristic of granites and pegmatites. In metamorphic rocks muscovite isthe primaryconstitu- ent of many mica schists. Biotite is found in igneous rocks ranging from granite pegmatites to diorites, gabbros, and peridotites. It also occurs in silica-rich lavas, porphyries, and a wide range of metamorphic rocks. Phlogopite occurs in metamorphosed magne- sium limestones, dolomites, and ultrabasic rocks. Le- pidolite occurs only in pegmatites. History Mining of mica started as early as 2000 b.c.e. in India, where it was used as medicine, decoration, and paint. Commercial mining of mica in the United States began in1803. Mica was used instore windows,shades for open light flames, and furnace viewing glass. When electronic vacuum tubes were developed in the early 1900’s, mica was used as spacers and insulators in the tubes, thus beginningits usein the electricalindustry. Obtaining Mica The United States has limited supplies of sheet mica but is the largest producer of scrap mica. Although there are noenvironmental problems inmining mica, sheet micais expensive tomine becauseof the intense hand labor needed to mine and process the sheets. Uses of Mica Muscovite and phologopite remain important com- mercially because they have a low thermal and electri- cal conductivity and a high dielectrical strength. Sheet mica is used as electrical insulators, retardation plates in neon helium lasers, optical filters, and washers in the computer industry. The isinglass used in fur- nace and stove doors from the 1800’s to the present is sheet muscovite. Lepidolite is the only mica mined and processed for itscomposition. It is a source oflith- ium, which is used in the production of heat-resistant glass. Scraps and flakes of mica are processed into ground mica and used as a coating on rolled roofing, asphalt shingles, and waterproof fabrics. It is also used in wall- paper to give it a shiny luster, as a lubricant when mixed with oils, and as a pigment extender in paint. A magnesium-rich alteration product of biotite, vermic- ulite, is used as insulation, packing material, and an ingredient in potting soil. Dion C. Stewart Web Site U.S. Geological Survey Mineral Information: Mica Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/mica/ See also: Lithium; Metamorphic processes, rocks, and mineral deposits; Pegmatites. Mineral deposits. See Igneous processes, rocks, and mineral deposits; Metamorphic processes, rocks, and mineral deposits; Plutonic rocks and mineral deposits; Sedimentary processes, rocks, and mineral deposits 746 • Mica Global Resources Drywall joint cement 59% Paint 13% Plastics 5% Other 23% Source: Historical Statistics for Mineral and Material Commodities in the United States U.S. Geological Survey, 2005, scrap and flake mica statistics,inT.D.KellyandG.R.Matos,comps., , U.S. Geological Survey Data Series 140. Available online at http://pubs.usgs.gov/ds/2005/140/. U.S. End Uses of Ground Mica Global Resources . eastern coast. By1917, large quantitiesof Mexicanoil were be - Global Resources Mexico • 741 742 • Mexico Global Resources Mexico: Resources at a Glance Official name: United Mexican States Government:. distillation of hard - Global Resources Methanol • 739 woods at temperatures below 400° Celsius. However, this method produced low yields (about 21 liters per metric ton of wood) of very impure. Sea and the Gulf of Mexico. The country’s western shore meets the Pacific Ocean, the Gulf of California, and the Gulf of Tehuantepec. Only about one-third of Mexico is flat. A chain of volcanic mountains