cubic meters, or almost equal to China’s total annual runoff. In addition to fisheries and transportation, irriga- tion, hydration, industrial, and numerous other uses, water resources in China are a significant energy re- serve. The total hydrological power reserve is esti- mated at 680 million kilowatts, ranking first in the world. Of thetotal, 380 million kilowatts can be devel- oped to generate1.9trillion kilowatt-hours of electric- ity, whichcontribute a great deal to China’s economic development and the world economy. Climate Resources China’s vast territory spans multiple climate zones from the south to the north, including tropical, sub- tropical, warm temperate, temperate, and boreal. In addition, the Qinghai-Tibet Plateau has a unique al- pine region. Nevertheless, the subtropical, warm tem- perate, and temperate climate zones compose ap- proximately 70 percent of the country. As diverse as the climate is, the basic characteristic is a continental monsoon climate, whichexhibits three mainfeatures: substantial daily and seasonal temperature differen- tial; uneven precipitation distribution, with a steady drop from the southeast to the northwest by a dra- matic 40:1ratio; and dramatic wind turnover between winter and summer. During the winter, cold and dry air from high latitude rises from the north. In sum- mer, warm and humid wind comes mainly from the ocean in the southeast. The average annualtemperatures in theeastern re- gion descendfrom south to north, from 25° Celsiusto 5.5° Celsius. Most of thewestern Qinghai-Tibet Plateau has annual average temperatures below 0° Celsius, but the Tarim basinis10°Celsius. The temperature differ- ential in the summer between the south and north is small, only 10° Celsius. In the winter, however,the tem- perature difference between these two regions can be as much as 50° Celsius. The lowest temperature in the Mohe area can dip below −50° Celsius. The average annual precipitation across China is 629 millimeters, with a steady decline in annual precipitation from southeast to northwest, which is somewhat similar to the annual temperature patterns. In general, high precipitation is concentrated in the summer months. Based on the annual rainfall pattern, China’s areas can be divided into 32 percent subhumid, 18 percent semihumid, 19 percent semiarid,and31percentarid. The temperature and annual precipitation pattern results in aconcentrated distribution ofagriculture in central and southeast provinces and the Sichuan ba - sin, areas that are thefoundation of China’s economy. The vast territory in the northwest is not productive and contributes little to China’s agriculture. Biological Resources China is blessed with rich biological resources. It has more wild animal species than any other country. Ver- tebrates alone accountfor5,200 species, 11 percent of the world’s total. Of these animals, 499 species are mammals, 1,186 are birds, 376 are reptiles, 279 are amphibians, and 2,804 are fish. This wildlife consists of many endemic species, including some of the most well-known and rare animals: the giant panda, golden-haired monkey, Chinese alligator, crested ibis, white-lipped deer, South China tiger, red-crowned crane, brown-eared pheasant, and Yangtze River dol- phin (though this animal is thought to be extinct). The diverse flora in China includes twenty-five thousand species of seed plants. From the tropical rain forests to the boreal coniferous forests, Chinahas almost all the natural vegetation characteristic of the Northern Hemisphere. The two hundred or so spe- cies of gymnosperms account for 25 percent of the world’s total. In addition, there are seven thousand species of woody plants andtwenty-nine hundred spe- cies of trees. Severalendemic plant speciesare consid- ered as “living fossils,” including ginkgo, metasequoia, and golden pine. China has more thanfivethousand years ofagricul- tural history, during which time the country has con- tributed many major crops important to humankind, including rice, soybeans, peaches, pears, plums, dates, grapefruit, lychees, and tea. Based on their utiliza- tion, China has one thousand plant species for timber wood, three hundred starchy plants,more than ninety vegetable species, and six hundred oil species. Its crops and germplasm continue to make vital contri- butions to the world’s economy. Mineral Resources China possesses deposits of all the discovered miner- als. China’s total reserve of 146 mineral resources ranks the country third among world nations. Coal, with a proved reserve of 877 billion metric tons, is found mainly in northern China, including the prov- inces of Shaanxi, Liaoning, Nei Monggol, and Hei- longjiang. Among the 250 or so petroliferous basins identified, more than half of them (130) are under development. 200 • China Global Resources The identified iron-ore reserves are estimatedat 41 billion metric tons and distributed in multiple re- gions. China also ranks among leading nations in re- serves of minerals such as tungsten, tin, antimony, zinc, molybdenum, lead, and mercury. China’s rare earth reserves are more than the rest ofthe world’s to- tal combined. In fact, China accounts for 80 percent of the world’s total reserves in that category. The diverse minerals and their large reserves provide im- portant raw materials and energy sources that will continue to power China’s economic growth and de- velopment. In 1996, China established a thorough (although not perfect) legal system for the exploration and ex- ploitation ofits minerals.This system consists of many laws, regulations, and rules promulgated by different levels of government authorities. Ononehand,China has encouraged foreign investment in mineral re- sources exploration and new mining technologies. On the other hand, China imports minerals from other countries and invests heavily in acquiring min- eral resources abroad. In 2008, China bought more than half of Australia’s mineral exports. China has be- come the world’s largest consumer of raw materials. Energy Resources China is rich in energy resources, but their distribu- tion is uneven. China ranks third among world na- tions in energy reserves and output, with a total en- ergy production equivalent to 11 billion metric tons of standard coal. In 2007, China’s coal output was 2.3 billion metric tons, which was top among countries; its crude oil output was 172 million metric tons, which ranked fifth; and its power generation capacity was 720 gigawatts, which was fourth. Gas production reached 76 billion cubic meters in 2007. China relies heavily on coal for energy, but 80 per- cent of the coal reserves are concentrated in the north. The most economically developed eight prov- inces south of the Chang River account for only 2 per- cent ofthe total coal reserves. About85 percent ofthe proved oil reserves are concentrated in the east re- gion, north of the Chang. Sixty-eight percent of hy- draulic power developed is in the southwest region. China has addressed the low energy reserves in the economically vibrant south through the construction of nuclear power plants. The rapid economic growth anddevelopment that began in 1982 have created an insatiable demand for fossil fuel (oil and gas) that far exceeds China’s own production capacity. Thus, China became a major im - porter of oil beginning in the early 1990’s. China im- ported 162 million metric tons of crude oil in 2007. A limit to China’s storagecapacityis the onlyreasonthat figure is not higher. That limit will soon change as China builds more strategic oil reserve facilities in the western region. In short, China has become the world’s second largest energy user, trailing only the United States. With an ever-increasing demand for oil, China is a driving force for energy consumption. This in turnwill have asignificantimpact on theworld economy and environment. Other Resources China is a country rich in tourism resources. Its vast territory and complex topography provide visitors to China with year-round opportunities. The natural scenery in thenorth presents thousands ofkilometers of glaciers and snowy land during the winter. The southern regions provide tourists with lush scenes of vegetation. China’s exotic flora and fauna, found in its many nationalnature reserves, attracttourists of all ages. China is dotted with magnificent rivers, lakes, mountains, and canyons. Its long cultural history has produced numerous world-class attractions. In addi- tion, the relatively low cost of travel and lodging, com- bined with the world’s burgeoning desire to know China, has fueled the powerful tourism engine in China. As one of the world’s four ancient civilizations, China is full of historical sites and cultural relics. Some of the most famous attractions include the Great Wall, the Terracotta Army, Ming Tombs, Peking Man, and many other attractions of historicaland cul- tural significance. Ming Y. Zheng Further Reading Forney, Matthew. “China’s Quest for Oil.” Time (Octo- ber 18, 2004). Lew, Alan A., and Lawrence Yu. Tourism in China: Geo- graphic, Political, and Economic Perspectives. Boulder, Colo.: Westview Press, 1995. National Geographic Society. NationalGeographicAtlas of China. Washington, D.C.: Author, 2007. Sheehan, Peter. Implications of China’s Rising Energy Use. Singapore: World Scientific, 2008. Xie, Jian, et al. Addressing China’s Water Scarcity: Recom - mendations for Selected Water Resource Management Is - sues. Washington, D.C.: World Bank, 2009. Global Resources China • 201 Zhang, Q., et al. “Precipitation, Temperature, and Runoff Analysis from 1950 to 2002 in the Yangtze Basin, China.” Hydrological Sciences Journal 50, no. 1 (2005): 65-80. Web Site CIA World Factbook https://www.cia.gov/library/publications/the- world-factbook/ See also: Agricultural products; Agriculture indus- try; Ecozones and biogeographic realms; Energy poli- tics; Hydrogen; Population growth; Three Gorges Dam. Chlorites Category: Mineral and other nonliving resources Chlorites are mostcommonlyfound as microscopic par- ticles in clays. They are also found in metamorphic rocks such as schists. Metamorphic chlorites are com- monly found in Michigan, Norway, the United King- dom, and Japan. Chlorites also occur in igneous rocks as a productof biopyriboles thathave been transformed by heat and moisture. They may also be found in sedi- mentary rocks formed from pieces of older igneous or metamorphic rocks containing chlorites. Definition The term “chlorite”(from theGreekword for “green”) refers to a variety of hydrous aluminum silicates of magnesium, iron, and other metals. They are soft green minerals with a glassy luster. Chlorites are brit- tle and can be ground into white or pale green pow- der easily. Thin sheets of chlorite are flexible but not elastic. Chlorites are agroup of silicateminerals consisting of alternating layers of molecules forming two kinds of two-dimensional sheets. One layer consists of sili- cate groups (one silicon atom bonded to four oxygen atoms) bound to aluminum atoms, hydroxyl groups (one oxygen atom bonded to one hydrogen atom), and magnesium, iron, or other metallic atoms. The other layer consists of magnesium, iron, aluminum, or other metallic atoms bound to hydroxyl groups. If most of the metallic atoms other than aluminum are magnesium, the mineral is known as clinochlore. If the metallic atoms are iron, it is known as chamosite. If they are nickel, it is known as nimite. If they are manganese, it is known as pennantite. These four minerals are very similar. Overview Chlorites are most useful in the form of clay minerals. They mix with other substances to form clays that are widely used in pottery and construction. Clay miner- als are also used in drilling “muds” (thick suspensions used to lubricate rotary drills). They may also be used as catalysts in petroleum refining and to decolorize vegetable oils. The density of chloriterangesfrom2.6to 3.3 grams per cubic centimeter. On the Mohs scale, they have a hardness between 2 and 2.5; they are generally soft enough to be scratched with a fingernail. Chlorite usuallyexists as amicroscopic component of clay, along with organic material, quartz, and other minerals. Visible pieces of chlorite may be found within a variety of rocks, particularly metamorphic rocks such as the very common schists. Chlorites are chemically similar to other clay min- erals (hydrous aluminum silicates) and are often found in combination with them. They are generally more resistant to heat than other clay minerals are. This fact is used to detect chlorite within clays. A sam- ple of the clay is heated to between 500° and 700° Cel- sius, whichbreaks downthe otherclay minerals. X-ray diffraction is then used to detect the layers of silicate chains that are characteristic of clay minerals. If this pattern is detected, chlorite is present in the sample. In other regards chlorites have about the same prop- erties as other clay minerals. Rose Secrest See also: Aluminum; Clays; Metamorphic processes, rocks, and mineral deposits; Silicates. Chromium Category: Mineral and other nonliving resources Where Found Chromium is a moderately abundant element that does not occur free in nature. Its principal ore is known as chromite, (Fe,Mg) (Cr,Al) 2 O 4 . The world’s chromite resources are concentrated in the Eastern 202 • Chlorites Global Resources Hemisphere, with major producers including South Africa, Kazakhstan, India, Zimbabwe, Turkey, Fin- land, and Brazil. Primary Uses Chromium is a strategic and critical resource used principally in the production of alloys and superal- loys, stainless steel, refractory materials, pigments, and chemicals. It is used for dyeing textiles and leather tanning and as a laboratory glassware cleanser. Fur- thermore, chromium in its trivalent oxidation state is an essential trace nutrient for humans and other mammals. Technical Definition Chromium (abbreviated Cr), atomic number 24, is a metallic chemical elementbelonging to Group VIBof the periodic table of the elements. It has four natu- rally occurring isotopes and an average molecular weight of51.996. Pure chromium is silver-gray, brittle, and hard. Its specific gravity is 7.19 at 20° Celsius, its melting point is approximately 1,890° Celsius, and its boiling pointis 2,200° Celsius. This lustrous metal will take a highpolishand does nottarnish inair.In chem- ical compounds chromium may have oxidation states ranging from −2to +6,but inmost compounds it is tri - valent (+3) or hexavalent (+6). The trivalent state is more common in naturally occurring compounds, while hexavalent chromium is frequently found in in- dustrial applications. Description, Distribution, and Forms Chromium is a commercially important metallic ele- ment. Forming compounds with brilliant red, yellow, and green hues, it derives its name from the Greek chroma (color). Its concentration in the lithosphere is 100 grams per metric ton. Total world production of chromite is about 20 million metric tons. Trivalent chromium, the form most often found in nature, is a trace element inthehuman body; bycontrast,hexava- lent chromium is a highly toxic substance whose con- centrations in the environment are regulated by law. Approximately 95 percent of the world’s chro- mium resources are found in southern Africa, with South Africa the leading producer in the region. Other world producers include Kazakhstan, India, Turkey, Finland, Brazil, and Russia. Chromium is present in a number of minerals, but chromite is its only commercial ore. Primary deposits of chromite occur as stratiform and podiform ores found in cer- tain types of ultrabasic (low-silica) rocks. Secondary alluvial deposits of chromite are formed by the weath- ering of stratiform (layered) and podiform ores. Stratiform chromite deposits are often several me - ters thick, extend over large areas, havea relatively uni - form composition, and frequently include platinum- Global Resources Chromium • 203 Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009.Source: Mineral Commodity Summaries, 2009 3,300,000 3,700,000 9,600,000 Withheld 4,900,000 Metric Tons Gross Weight 10,500,0009,000,0007,500,0006,000,0004,500,0003,000,0001,500,000 United States India Kazkhstan South Africa Other countries U.S. data were withheld to avoid disclosure of company propriety data.Note: Chromium: World Mine Production, 2008 bearing zones. They formed as chromite crystallized and precipitated from silicate melts. Examples in- clude the Bushveld Igneous Complex in Transvaal, South Africa; the Great Dyke in Zimbabwe; and the Stillwater Complex in Montana. Stratiform deposits constitute more than 90 percent of the world’s identi- fied chromite reserves. All the commercially signifi- cant stratiform chromites are Precambrian in age and occur in stable cratons, portions of the Earth’s crust that have experienced little deformation over a long period of geologic time. In podiform deposits, chromite occurs as irregular pods or lenses within the host rock. Major podiform deposits are found in Kazakhstan, Albania, Greece, Turkey, Zimbabwe, Cuba, and the Philippines. Po- diform chromites form along island arcs and mobile mountain belts, and most are of Paleozoic age or younger. Chromium occurs in nature only in combination with other elements. The most important chromium ore is chromite, a brownish-black to iron-black min- eral of the spinel group. It occurs as octahedral crys- tals, irregular masses, and alluvial deposits. Other minerals that contain chromium include the gem- stones emerald and aquamarine, which owe their dis- tinctive colors to the element. Chromium plays a role in the body’s glucose toler- ance. Moderate amountsoftrivalent chromium inthe diet have no apparent harmful effects. Chromium metal is biologically inert and has no known toxicity. While trivalent chromium compounds exhibit lit- tle or no toxicity, hexavalent chromium is a systemic poison and an irritant and corrosive. It can be ab- sorbed by ingestion, inhalation, or dermal exposure. Ulcerations of the skin and mucous membranes may result from exposure. Chromate salts are suspected human carcinogens that may produce tumors of the lungs, nasal cavity, and paranasal sinuses. The 1974 Safe Drinking Water Act set the maximum allowable concentration for total chromium in drinking water in the United States at 100 micrograms per liter. In general, chromium does not naturally occur in high concentrations in water. Elevated chromium lev- els in surface water or groundwater are typical be- cause of contamination from runoff from old mining operations or improper disposal of electroplating wastes. However, in the groundwater of Paradise Val- ley in Maricopa County, Arizona, hexavalent chro - mium of natural origin is present in concentrations exceeding 200 micrograms per liter. The alkaline groundwater causes naturally occurring trivalent chro - mium in thesoil to oxidizeto soluble hexavalentchro- mium. History Chromium appears to have been unknown to ancient civilizations. It was discovered in 1797 by Louis- Nicolas Vauquelin, a French chemist, when he found that the leadinasample of crocoite (PbCrO 4 )fromSi- beria was combined with an unknown oxide mineral. Between the time of chromium’s discovery and 1827, the primary source of chromite was the Ural Moun- tains of Russia. In 1827, the discovery of chromite in Maryland moved the United States to the forefront of world production. Large Turkish deposits were devel- oped in the 1860’s; after this time, the Eastern Hemi- sphere became the chief source of chromite. The chemical manufacturing industry was the main con- sumer of chromium until the early 1900’s, when the element found increasing use in metallurgical andre- fractory products. During World Wars I and II, the United States increased its domestic production of the metal, and during the 1950’s it stockpiled domes- tic ores. International political conflicts have often led to interruptions in chromium supply. Obtaining Chromium Sodium dichromate, from which most commercial chromium compounds are made, is produced by roasting chromite with sodium carbonate, leaching the resulting product with water, and concentrating and acidifying the leachate to cause sodium dichro- mate to precipitate. Ferrochromiumis prepared from chromite by reducing the ore with carbon in a blast furnace. Metallic chromium is obtained by reducing chromium oxide with aluminum or carbon, or by electrolyzing a solution of ferrochromium dissolved in sulfuric acid after the iron has been removed from the solution as ferrous ammonium sulfate. Chromium metal in its purest form is produced in small quanti- ties by vapor deposition from anhydrous chromium iodide. Uses of Chromium The principal use of chromium is as an alloy metal, particularly in the steel industry. Combined with other metals, it imparts hardness, strength, and resistance to corrosion andheat. Chromium facilitates the hard - ening of steel and, if the alloy’s carbon content is high, enables it to withstand extreme abrasion and 204 • Chromium Global Resources wear. In ball-bearing steel, chromium improves the elastic limit and imparts an evenly distributed hard- ness. Chromium increases the corrosion resistance of stainless steel and is an important alloy metal in heat- resisting steels. High-chromium steel, with its high re- sistance to wear, is used for making items such as die blocks, press plates, chisels, hacksaw blades, and cir- cular steel saws. Nichrome, an alloy of nickel and chromium, is used as a heating element in household appliances such as electric toasters and coffeepots. Stellite, an extremely hard alloy of cobalt, chromium, and tungsten with minor amounts of iron, silicon, and carbon, is used in metal cutting tools and wear- resistant surfaces. A similar alloy, which employs mo- lybdenum rather than tungsten, is used in surgical tools. With its hardness and nontarnishing proper- ties, chromium is also an ideal electroplating metal. Chromium’s uses in alloys and plating make it an im- portant strategic and critical metal. Chromite is a valuable raw material for the manu- facture of refractory materials such as refractory bricks, foundry sand, and casting items for furnaces used in metallurgy. Refractory materials are able to withstand high temperatures and contact with often corrosive gases and molten materials. Chromite is fre- quently used in combination with other refractory materials; for instance, mixed with the magnesium ore magnesite (magnesium carbonate) and fused in an arc furnace it is cast into refractory brick. Various chromates and dichromates, salts of chro- mic acid, are used as pigments in paints and dyes, yielding vivid yellows, reds, oranges, and greens. Chromium hydroxide is used as a mordant in textile dyeing. Potassium dichromate mixed with sulfuric acid is used as a cleanser for laboratory glassware. Chromium compounds are also used in chemical manufacture and leather tanning. Karen N. Kähler Further Reading Adriano, Domy C. “Chromium.” In Trace Elements in Terrestrial Environments:Biogeochemistry, Bioavailabil- ity, and Risks of Metals. 2d ed. New York: Springer, 2001. Greenwood, N. N., and A. Earnshaw. “Chromium, Molybdenum, and Tungsten.” In Chemistry of the El- ements. 2d ed. Boston: Butterworth-Heinemann, 1997. Guertin, Jacques, et al., eds. Chromium (VI) Handbook. Boca Raton, Fla.: CRC Press, 2005. Independent Environmental Technical Evaluation Group. Chromium (VI) Handbook. Edited by Jacques Guertin, James A. Jacobs, and Cynthia P. Avakian. Boca Raton, Fla.: CRC Press, 2005. Katz, Sidney A., and Harry Salem. The Biological and Environmental Chemistry of Chromium. New York: VCH, 1994. Kogel, Jessica Elzea, et al., eds. “Chromite.” In Indus- trial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: Society for Mining, Metallurgy, and Exploration, 2006. Manning, D. A. C. Introduction to Industrial Minerals. New York: Chapman & Hall, 1995. Nriagu, Jerome O., and Evert Nieboer, eds. Chromium in the Natural and Human Environments. New York: Wiley, 1988. Udy, Marvin J. Chemistry of Chromium and Its Com- pounds.Vol1ofChromium. New York: Reinhold, 1956. Web Sites Natural Resources Canada Canadian Minerals Yearbook, Mineral and Metal Commodity Reviews http://www.nrcan-rncan.gc.ca/mms-smm/busi- indu/cmy-amc/com-eng.htm U.S. Geological Survey Chromium: Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/chromium See also: Alloys;Brazil;India;Kazakhstan; Metals and metallurgy; Plutonic rocks and mineral deposits; Rus- sia; South Africa; Steel; Strategic resources; Turkey; United States. Civilian Conservation Corps Category: Organizations, agencies, and programs Date: Established 1933 The Civilian Conservation Corps, a central part of Franklin D. Roosevelt’s “New Deal,” was conceived as a comprehensive project which would encompass relief for the unemployed, recovery of the nation’s economic health, and conservation of American natural re - sources. Global Resources Civilian Conservation Corps • 205 Background In 1934, President Franklin D. Roose- velt noted that the United States was one of the few industrialized countries that had notestablisheda “national pol- icy forthe development ofour land and water resources.” This lack was in the process of rectification when, inMarch, 1933, shortly after his inauguration, Roosevelt proposed the establishment of the Civilian Conservation Corps (CCC). The legislationprovided forthe voluntary mobilization of unemployed young men to work on various conser- vation projects throughout the nation. As Congress did on most of Roose- velt’s proposals during his first one hun- dred days in office, it acted swiftly, ap- proving the legislation on March 31, 1933. Administered by the Labor De- partment, the Army, the Forestry Ser- vice, and the National Park Service, the CCC had the potential to be an administrative disas- ter, but disaster did not happen. By July more than 300,000 unemployed young men, aged eighteen to twenty-five and from families on relief, were already working in the CCC’s thirteen hundred camps. By 1935, there were more than 500,000 men in the CCC, and before it was dismantled more than 2.5 million young men hadjoined,workingfor one dollar adayin twenty-five hundred camps. Impact on Resource Use The projects were varied, ranging from restoring bat- tlefields of the American Revolution and Civil War to constructing trails intheHigh Sierra; from protecting wildlife (including stocking almost one billion fish) and building fire lookout towers to planting two bil- lion trees—200 million as windbreaks in the Dust Bowl. Estimates indicate that of all the forests planted in the history of the United States, both public and private, more than half were planted by the so-called tree peopleof theCCC. From the east and west, north and south, farm boys worked alongside young men from the cities. The CCC was organized on a military basis, although participation was voluntary, and one could enter and leave when one wished. Most men stayed from several months to about one year. Although women were excluded and African Amer - icans were subject to a 10 percent quota and were usu - ally segregated, as a conservation organization, the CCC was aninstant and lastingsuccess.Many of Amer- ica’s natural resources were preserved during those few years of the 1930’s in spite of the predictions by some that many of the projects were beyond the gov- ernment’s powers andthattheCCC would be inimical to capitalism or to organized labor because of the CCC’s low wages. Some feared that the CCC smacked of communist collectivism or fascist militarism. Not the least of the resources conserved were the young men themselves, whose experience developed their physical bodies as well as their intellectual and emo- tional capabilities. At the onset of World War II the CCC was terminated, but individual states later estab- lished their own conservation corps, such as the Cali- fornia Conservation Corps. John F. Kennedy’s Peace Corps was also inspired in part by the CCC. Eugene Larson Web Sites Civilian Conservation Corps Civilian Conservation Corps Legacy http://www.ccclegacy.org/ National Archives Records of the Civilian Conservation Corps http://www.archives.gov/research/guide-fed- records/groups/035.html#35.4 206 • Civilian Conservation Corps Global Resources Members of the African American Civilian Conservation Corps reconstruct gabions at the French Battery along York-Hampton Road in Yorktown, Virginia, in the mid- 1930’s. (National Park Service Historic Photograph Collection) See also: Conservation; Dust Bowl; Forest Service, U.S.; Reforestation; Roosevelt, Franklin D. Clays Category: Mineral and other nonliving resources The term “clay” may be used to describe a groupof fine- grained minerals, a type of rock, or a range of particle size, generally less than four micrometers. As a rock term, clay is generally understood to mean an earthy, fine-grained material formed largely of crystalline minerals known as the clay minerals. Background Clays can be found throughout the world, but eco- nomically valuable deposits are limited in extent and distribution. Majorkaolin deposits inthe UnitedStates are found in Georgia and SouthCarolina.The world’s major bentonite deposits are found in Wyoming and Montana, and large fuller’s earth deposits can be found in Georgia and Florida. Ball and refractory clays are abun- dant in Kentucky and Tennessee. Clays are used in a number of applications requiring the incorporation of fine-grained materials that contribute to a product’s physi- cal or chemicalproperties. Usesincludefillers in paint, paper, and plastics, additives to drill- ing muds, the manufacture of ceramics and brick, carriers for pesticides and insecticides, the manufacture of catalysts, and cosmetic and pharmaceutical uses. Clays are considered “industrial minerals,” a group of minerals composed of geological materials having commercial value and of a nonmetallic, nonfuel character. They may be marketed in a natural, as-mined state or as processed materials. Clays can vary widely in composition andphysical characteristics.Cer- tain similarities exist among a number of clays, however,and they canbecategorized in broad terms as kaolin, bentonite or fuller’s earth, ball clay, and refractory clay based on similari- ties in either composition or functional per- formance. Clays that donot fall intoany of the major categories are generally referred to as common clay or shale. Mineralogy and Chemistry Clays are hydrous (water-containing) aluminum sili- cates containing alkalies or alkaline earth elements. Magnesium or iron may substitute wholly or partially for aluminum in the clay mineral structure. Clay min- erals are composed of alternating layers of two differ- ent atomic structures. The first is an aluminum-bear- ing octahedral sheet structure, and the second is a layer of silica tetrahedrons. The aluminum and sili- con atoms are chemically bonded to oxygen in these layers, which are held to one another by weaker elec- trostatic bonds. Interlayer sites in many clays contain water molecules or cations such as calcium, sodium, potassium, magnesium, lithium, or hydrogen. The presence or absence of interlayer molecules affects both the physical andchemicalpropertiesof the clay. Kaolin Kaolin is a clay consisting predominantly of pure kaolinite or related clay minerals. Most major depos- Global Resources Clays • 207 Bricks and concrete block 65% Structural concrete 3.5% Portland & other cements 19% Ceramics, glass, & tile 3% Other 9.5% Source: Historical Statistics for Mineral and Material Commodities in the United States Note: U.S. Geological Survey, 2005, clay and shale statistics, in T. D. KellyandG.R.Matos,comps., ,U.S.GeologicalSurvey Data Series 140. Available online at http://pubs.usgs.gov/ds/ 2005/140/. “Other” includes ceramics and glass, floor and wall tile, highway surfacing, other lightweight aggregates, refractories, and other heavy clay products. U.S. End Uses of Clay and Shale its of kaolin are referred to as either primary (resid - ual) or secondary. Primary deposits are formed in place as the weathering products of granite or other feldspar-rich rocks. Other minerals associated with deposits of this type include quartz, micas, amphi- boles, tourmaline, and unweathered feldspars. Pri- mary deposits are irregular in shape, grading down- ward into unaltered parent (source) rock. Secondary deposits of kaolin are sedimentary ac- cumulations of kaoliniticmaterial thathas been trans- ported from its source area. Deposits of this type may contain up to 95 percent kaolinite; in contrast, pri- mary deposits maycontain as littleas10 percent. Asso- ciated minerals may include quartz, micas, other clay minerals, and a variety of high-density “heavy miner- als.” Secondary deposits are generally lenticular or tabular in shape, with thicknesses up to sixty meters and areal dimensions of up to about two kilometers. Kaolin isalso found asa product ofhydrothermally altered rocks. Deposits of this nature are of limited size and extent. They occur as irregularly elongated pods or pipelike bodies along faults, joints, and other conduits along which hot solutions have flowed. Kaolin is generally soft and plastic, although harder silica-bearing varieties also exist. Crystals of kaolinite are hexagonal, composed of individual platelets stacked in an accordion-like manner. There is little ionic substitution in the crystal lattice. Kaolin has numerous industrial usesandis perhaps best known foritsuse in themanufactureof china and porcelain. Its chemical inertness, high brightness, white color (either naturally or resulting from pro- cessing and beneficiation), and crystal shape make it useful in other applications as well. Kaolin is used as a filler or coating in themanufacture of paper, asa filler in paint, plastics, and pharmaceuticals, and in the manufacture of rubber, tile, brick, ink, adhesives, de- tergents, cosmetics, pencils, pastes, and other con- sumer products. Ball Clay and Refractory Clay Ball clays are composed of up to 70 percent kaolin. They generally occur in secondary sedimentary de- posits characterized by thepresence oforganicmatter along with varying amounts of other clays, quartz, feldspar, calcite, and heavy minerals.Sedimentary de- posits of ball clay represent accumulations of clay ma- terials that were derived from a number of sources and that were deposited in nonmarine environments. Most deposits are lenticular, with areal dimensions of up to 850 meters and thicknesses of up to 10 or more meters. 208 • Clays Global Resources Clay and Shale: World Mine Production, 2008 Metric Tons Nation Bentonite Fuller’s Earth Kaolin Brazil (beneficiated) 240,000 — 2,490,000 Commonwealth of Independent States (crude) 750,000 — 6,200,000 Czech Republic (crude) 220,000 — 3,800,000 Germany (sales) 385,000 — 3,850,000 Greece (crude) 950,000 — 60,000 Italy (kaolinitic earth) 600,000 3,000 580,000 Mexico 435,000 100,000 960,000 South Korea (crude) — — 2,600,000 Spain 105,000 870,000 450,000 Turkey 930,000 — 580,000 United Kingdom — — 1,750,000 United States (sales) 4,870,000 2,630,000 6,750,000 Other countries 2,520,000 297,000 8,630,000 Source: Data from the U.S. Geological Survey, Mineral Commodity Summaries, 2009. U.S. Government Printing Office, 2009. Ball clays are plastic or semi-plastic and are used to provide strength and malleability to ceramic bodies prior tofiring. They fuse during firing, also acting as a “cement” to bind together the refractory, nonshrink- ing component of a ceramic body. Ball clay is used to manufacture tableware, stoneware, tiles, plumbing fixtures, and bricks. It is also used as a sealant in land- fills. Refractory clays are generally kaolin, containing only small quantities of micaor iron-bearing minerals that might combinewithother materials duringfiring to form low-melting-point glasses. Refractory clays have a high heat resistance. Other properties that af- fect overall quality include shrinkage, warping, crack- ing, and abrasion. Refractory clays can be soft and plastic or hard like flint. They generally occur as sedi- mentary deposits that are lenticular or tabular in shape. They are mined for use in the manufacture of firebrick, insulating brick, and other heat-resistant clay products. Bentonite and Fuller’s Earth “Bentonite” is generally understood to mean a clay consisting of minerals from the montmorillonite group, regardless of origin or occurrence. The most important commercial montmorillonites are the so- dium and calcium varieties. Sodium montmorillonite (Wyoming or western bentonite) hashigh swelling ca- pabilities when addedto water. Calciummontmorillo- nite (southern bentonite) has a lower swelling capac- ity, and it generally crumbles when added to water. Other montmorillonites include those rich in lithium (hectorite), magnesium (saponite), or iron (non- tronite). Bentonite can be both physically and chemically reactive. It shrinks or swells as it releases or absorbs interstitial water or organic molecules, and it has important cation exchange and chemical sorption properties. Bentonite’s physical and chemical prop- erties account for its usefulness in modifying fluid viscosity or plasticity; it also has a variety of other uses. Bentonites can be modified through chemical treatment to enhance selected physical or chemical properties. Wyoming bentonites are suitable for use in an as- mined condition.They are usedas anadditive in drill- ing mudto increase viscosityand aidin theremoval of drillhole cuttings. The clay also helps maintain cut - tings in suspensionand creates animpervious coating on thewall of thedrillhole toprevent fluid lossduring drilling. Southern bentonitescanbe modifiedtohave properties similar to Wyoming bentonites, but their use is generallyrestricted to otherapplicationssuchas binding iron ore during pelletizing and the manufac- ture of catalysts and no-carbon-required (NCR) copy papers. Bentonites are also used to refine, decolor, and purify oils and beverages; to manufacture fire re- tardants; and as hydraulic barriers. “Fuller’s earth” refers to clays (generally benton- itic) suitable for bleaching and absorbent or other special uses. The term was first used to describe mate- rials used for cleansing or fulling wool (removing lanolin and dirt), but it is now used more broadly to include decolorizers or purifiers in filtering applica- tions. Fuller’s earth products include cat litter, pesti- cide and insecticide carriers, soil conditioners, light- weight aggregate, and pharmaceuticals. Mining and Processing Most clay deposits are mined from open pits, al- though some are mined by underground methods. Open-pit mining generally involves the stripping of overburden, excavation of the clay, and transport of mined material to the processing plant. Some opera- tions may require blasting. The simplest operations involve excavation, trans- port to the plant, drying, and shipment to the cus- tomer. More complex operationsmayrequirethat the mined material first be put into a slurry form for re- moval of grit or sand, with transport to the plant by pipeline. Clay slurries can be chemically or physically treated to remove contaminants that contribute to discoloration or poor chemical or physical perfor- mance. They can then be filtered and dried prior to packaging and shipment to the customer. Some clays are put back into slurry form prior to shipment, de- pending upon a customer’s needs. Kyle L. Kayler Further Reading Bergaya, Faïza, Benny K. G. Theng, and Gerhard Lagaly, eds. Handbook of Clay Science. New York: Elsevier, 2006. Chatterjee, Kaulir Kisor. “Clay.” In Uses of Industrial Minerals, Rocks, and Freshwater. New York: Nova Sci- ence, 2009. Kogel, Jessica Elzea, et al., eds. “Clays.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: Society for Mining, Metal - lurgy, and Exploration, 2006. Global Resources Clays • 209 . economy. Mineral Resources China possesses deposits of all the discovered miner- als. China’s total reserve of 146 mineral resources ranks the country third among world nations. Coal, with a proved reserve of. pow- der easily. Thin sheets of chlorite are flexible but not elastic. Chlorites are agroup of silicateminerals consisting of alternating layers of molecules forming two kinds of two-dimensional sheets aninstant and lastingsuccess.Many of Amer- ica’s natural resources were preserved during those few years of the 1930’s in spite of the predictions by some that many of the projects were beyond the