Encyclopedia of Global Resources part 75 pps

Further Reading Atlas, Ronald M., and Richard Bartha. Microbial Ecol- ogy: Fundamentals and Applications. 4th ed. Menlo Park, Calif.: Benjamin/Cummings, 1998. Burkin, A. R. “Chemistry of Leaching Processes.” In Chemical Hydrometallurgy: Theory and Principles. Lon- don: ICP, 2001. Keller, EdwardA.EnvironmentalGeology. 8thed.Upper Saddle River, N.J.: Prentice Hall, 2000. Killham, Ken. Soil Ecology. New York: Cambridge Uni- versity Press, 1994. Madigan, Michael T., John M. Martinko, Paul V. Dunlap, and David P. Clark. Brock Biology of Microor- ganisms. San Francisco: Pearson/Benjamin Cum- mings, 2009. Marsden, John, and C. Iain House. “Leaching.” In The Chemistry of Gold Extraction. 2d ed. Littleton, Colo.: Society for Mining, Metallurgy, and Exploration, 2006. Robertson, G. P., and P. M. Groffman. “Nitrogen Transformations.” In Soil Microbiology, Ecology, and Biochemistry, edited by Eldor A. Paul. 3d ed. Boston: Academic Press, 2007. See also: Biotechnology; Igneous processes, rocks, and mineral deposits; Mining wastes and mine recla- mation; Secondary enrichment of mineral deposits; Sedimentary processes, rocks, and mineral deposits; Soil degradation. Lead Category: Mineral and other nonliving resources Where Found Lead iswidely distributed inthe Earth’s crust; it hasan estimated percentage of the crustal weight of 0.0013, making it more common than silver or gold but less common then copper or zinc; these are the four min- erals with which lead is most commonly found in ore deposits. All five may occur together in a deposit, or only two or three may occur in concentrations suffi- ciently rich to be economically attractive to miners. Primary Uses The major use of lead in the United States is in the lead-acid batteries used in automotive vehicles. Be - cause lead is so toxic, a fact that has been known since ancient times, many of its former uses have been cur - tailed or discontinued. While it is still used in cables, ammunition, solders, shielding of radiation, and elec- trical parts, its use as an antiknock additive in gasoline was phased out during the 1970’s and 1980’s. Never- theless, lead production has been maintained at about the same level as before the phase out. Should a suit- able substitute ever be developed for lead-acid batter- ies, the use of lead will decline to very low levels. Technical Definition Lead (abbreviated Pb), atomic number 82, belongs to Group IV of the periodic table of the elements. It is a mixture of four stable isotopes and has twenty-seven other isotopes, all radioactive, resulting from the fact that lead is the end product of three series of radioac- tive elements: the uranium series, actinium series, and thorium series. It has an average atomic weight of 207.2 and a density of 11.35 grams per cubic centime- ter; it has a melting point of 327.5° Celsius and a boil- ing point of 1,740° Celsius. Description, Distribution, and Forms Lead is soft, malleable,and ductile, and is second only to tin in possessing the lowest melting point among the common metals. It may well have been the first metal smelted by humans, although it was probably not the first metal used—an honor claimed by gold, silver, or copper, which occur naturally in their metal- lic states. The fact that the principal ore of lead, galena (lead sulfide), frequently resembles the metal itself in its gray-black metallic color probably encour- aged early humans to experiment with crude smelt- ing. Inorganic lead also occurs as a carbonate (cer- rusite), sulfate (anglesite), and oxides. Organic compounds of lead exist; these were used for many years in automobile gasoline as antiknock additives (tetraethyl and tetramethyl lead). Lead is widely dis- tributed in the environment, but except in bedrock, concentrations are largely a consequence of human activity. Clair Patterson demonstrated that dramatic human-related increases in lead concentrations exist in the oceans, in polar ice sheets, and in the atmo- sphere. Before the human use of lead, the global flux into the oceans was only one-tenth to one-hundredth what it is today; lead in the atmosphere has increased a hundredfold globally and a thousandfold in urban areas. Considering that only an estimated 0.0013 percent of the Earth’s crust is lead, it is surprisingly widely dis - 688 • Lead Global Resources tributed in the environment. Lead is found in both crystalline (igneous and metamorphic) and sedimen- tary rocks. Because it is the stable end product of ra- dioactive disintegration of minerals that form in igne- ous rocks (it is the rate of this disintegration that is employed to determine the age of the rock), virtually all oldercrystalline rocks containat leasttinyamounts of lead. As sedimentary rocks are derived from the weathering, erosion, and sedimentation of fragments from existing rocks, it follows that lead compounds will be among those that are sedimented. The higher concentrations of lead—those thatposetoxicity prob- lems or are valuable to miners—depend upon quite different processes. Some toxic concentrations of lead are transported by water and then sedimented or ab- sorbed by rock particles, depending on the salinity or acidity levels of the solution. Most toxic concentra- tions of lead, however, are transported as dust by the atmosphere. Deposits of lead ore exist at far higher concentra - tions than those levels that pose problems in water, dust, or soil. They are the result of natural geologic Global Resources Lead • 689 Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009.Source: Mineral Commodity Summaries, 2009 47,000 145,000 35,000 335,000 53,000 48,000 69,000 440,000 300,000 Metric Tons of Lead Content 1,750,0001,500,0001,250,0001,000,000750,000500,000250,000 United States Poland Peru Morocco Mexico Kazakhstan South Africa Sweden Other countries 576,000 95,000 1,540,000 85,000 56,000 Ireland India China Canada Australia Lead: World Mine Production, 2008 processes, including igneous intrusions, mountain building, and the flow of hot and cold solutions through bedrock over millions of years. The richest lead ores may contain 20 to 25 percent lead, usually with substantial fractions of zinc and minor quantities of silver. Copper and gold are also frequently associ- ated with lead deposits, or vice versa (minor amounts of lead are usually found in copper ore). Lead affects the environment in two major ways: through mining and processing, and because many of its uses, particularly in the past, have exposed the general public to its toxicity. Lead mining has envi- ronmental impacts similar to those of the mining of any mineral. Surface mining destroys the local eco- system and disrupts the use of land for other pur- poses; reclamation rarely prepares the land for as valuable a use as it enjoyed before mining. The major- ity of lead is mined underground, where surface dis- ruption is not as great unless subsidence over the mined areas is a problem. In both surface and un- derground mining, water is generally contaminated, mine wastes must be stored (waste dumps frequently occupy more space than the mine itself), and the transportation of mine products and waste serves as a source of dust, noise, and disruption to the surround- ing population. Themilling, smelting, and refining of lead pose further problems. First, lead itself escapes and pollutes the atmosphere with toxic substances. Second, most lead is derived from sulfides, which upon heating in the smelting and refining processes form sulfur dioxide. Sulfur dioxide combines with water in the atmosphere to create sulfuric acid, which devastates and denudes the vegetation cover in the immediate vicinity and contributes toacid rain fallout generally. Humans may come into contact with lead and its toxic effects in the air, dust, and water, and by direct contamination offood, drink, or cosmetics.The effects of lead on human health are diverse and severe, with their greatest impact on children. The effects are exac- erbated by the fact that lead accumulates in the body, and damage is often irreversible—especially damage to the brain. Lead damages blood biochemistry, the renal and endocrine system, liver functions, and the central nervous system, and it contributes to osteopo- rosis, high blood pressure, and reproductive abnor- malities. The Environmental Protection Agency and the Occupational Safety and Health Administration set standards of acceptable levels of lead in air, dust, soil, and water; the standards are updated frequently based on new research, and they are quite complex, depending on the duration and nature of exposure. History While lead apparently was not the first or second metal toattract early humans, becauseit did notoccur in a metallic state, it was exploited relatively early and may have been smelted in Anatolia (modern day Tur- key) as early as 7000-6500 b.c.e. The softness and mal- leability of lead proved to be both attractive and unde- sirable to people in antiquity. Most early lead mining was carried on to recover the associated silver, and the lead remaining from the process was piled in waste heaps. Lead may be strengthened by alloying with other metals, but this process was carried out only to a limited degree in lead’s earliest usage. While lead may not have proved attractive for uses requiring strength and hardness, its malleability caused the Romans, in particular, to put it to wide- spread use in piping,roofing, and vessels. In addition, lead compounds were used in paints, cosmetics, and as additives to wine and food. Lead poisoning was therefore widespread. The problem was recognized possibly as early as 370 b.c.e. by Hippocrates and cer- tainly was known by Nikander in the second century b.c.e. The Romans nevertheless continued to press lead into a variety of services until the fall of their em- pire. Some authorities believe that lead poisoning was central to this fall, and many more believe that it at least contributed (especially to the disorganization of Roman leaders). Others maintain that the critical lead-related factor in the decline of Rome was the ex- haustion of the richer silver-bearing ores. Exhaustion of mines or ores at any period in history is usually a function of the technology and economics of the time; many of these ores were particularly rich by modern standards. Silver was critical to maintenance of the Roman financial system, and the decline in its availability brought economic chaos. Medieval production of lead declined dramatically in Europe following the fall of the Roman Empire, al- though recurring cases of lead poisoning during this period serve as a reminder that lead was still utilized widely in storage vessels. The Industrial Revolution, beginning with its earliest stages, revived the produc- tion level of lead, both for itself and as a by-product of silver mining. The expansion of European explora- tion into the Western Hemisphere and of European colonization worldwide from the fifteenth century onward undoubtedly contributed to the rise in lead 690 • Lead Global Resources production. Gold and silver were sought avidly in these expansions of domain, and lead mining fre- quently serves as thefinaluse or “mop-up”stage in the life history of a mining district. Also, industrial uses and mining technology became increasingly sophisti- cated, leading to a new demand for lead and zinc, its frequent associate, especially beginning in the nine- teenth century. The production curve of lead and zinc goes exponentially upward through history, with far greater production todaythan inearlier centuries. Obtaining Lead The largest lead deposits in the United States and Eu- rope are ofthe Mississippi Valley type: leadsulfide (ga- lena) deposits of uncertain origin in limestone or do- lomite rocks. Many large mines throughout the world are found in crystalline rocks, where they are usually associated with igneous intrusions. Some lead is re- covered as a by-product of the mining of copper or other associated minerals from large open-pit mines developed in low-grade ores, called porphyries. This type of recovery is a triumph of modern technology and engineering, because the ores frequently contain less than 0.5 percent copper, with even smaller frac- tions of lead. Most lead is recovered from under- ground mines that are exploiting much smaller con- centrations in veins or disseminated beds of lead-zinc, zinc-lead, or lead-silver ores. From 2003 to 2007, the average U.S. primary lead production (lead from mines) was 162,000 metric tons per year, while production of secondary lead (recycled from scrap, chiefly automotive bat- teries) during the same time period was 1.2million metric tonsper year. World mine production was some- what less than lead from secondary sources: about 3.5 million metric tons from mines compared to 3.8 million metrictons fromsecondary sources. Recycling should prove even more important in the future as the richest deposits—those in which the lead content of the ore ranges between 5 and 10 percent— are depleted. This type of “exhaus- tion” of a deposit is a function of the prevailing technology and eco- nomics. In the first half of the twen - tieth century, the tristate lead-zinc mining district of Missouri, Okla - homa, and Kansas was the world’s greatest. Produc - tion there essentiallyceased in the1950’s, notbecause the lead and zinc were literally exhausted but because the concentrations available dropped below the level at which mining could be done profitably. Technology is continuously improving, however, and the history of mining is filled with examples (par- ticularly concerning the five associated metals gold, silver, copper, lead, and zinc) in which improvements in technology, combined with changing economic conditions, have made it possible to reopen or rework older and less attractive deposits. Some mine tailings or waste dumps have been reworked several times un- der these circumstances. Uses of Lead More than most metals, the uses to which lead and lead compounds have been put have changed consid- erably throughout history. One reason is that new op- portunities have presented themselves, such as auto- motive lead-acid batteries, the shielding of dangerous radiation, and antiknock additives for gasoline—all twentieth century phenomena. Largely, however, this has occurred because people have become increas- ingly cognizant ofthe dangers posed bylead’s toxicity. While the dangers of exposure to lead have been known since Greek and Roman times, in few cases has this led to regulation of uses. Not until the 1960’s, 1970’s, and 1980’s were specific controls or regula- tions imposed restricting the use of lead in paint pig- ments, as an additive to gasoline, and in construction. Global Resources Lead • 691 U.S. End Uses of Lead Percentage Uses 88 Lead-acid batteries 10 Ammunition, casting material, pipes, radiation shields, traps, extruded products, building construction, cable covers, caulking, solder, oxides (for ceramics, chemicals, glass, pigments) 2 Ballast, counterweights, brass, bronze, foil, terne metal, type metal, wire, other Source: Data from the U.S. Geological Survey, Mineral Commodity Summaries, 2009. U.S. Government Printing Office, 2009. Lead piping is still found in structures built in the 1970’s; the use of lead in storage vessels for food or drink has been regulated even more recently. Lead foil was used in capping wine bottles into the early 1990’s, andmany people are still unawarethat storage of wine or other liquids in fine leaded-glass decanters permits leaching of the lead content into the fluid over time. The post-World War II era saw the elimination or substantial reduction of the following uses of lead: water pipes, solder in food cans, paint pigments, gaso- line additives, and fishing sinkers. The major remain- ing uses include storage batteries, ammunition, paint pigments (for nonresidential use), glass and ceram- ics, sheet lead (largely for shielding against radia- tion), cable coverings, and solder. Neil E. Salisbury Further Reading Adriano, Domy C. “Lead.” In Trace Elements in Terres- trial Environments: Biogeochemistry, Bioavailability, and Risks of Metals. 2d ed. New York: Springer, 2001. Casas, José S., and José Sordo, eds. Lead: Chemistry, An- alytical Aspects, Environmental Impact, and Health Ef- fects. Boston: Elsevier, 2006. Cheremisinoff, Paul N., and Nicholas P. Cherem- isinoff. Lead: A Guidebook to Hazard Detection, Re- mediation, and Control. Englewood Cliffs, N.J.: PTR Prentice Hall, 1993. English, Peter C. Old Paint: A Medical History of Child- hood Lead-Paint Poisoning in the United States to 1980. New Brunswick, N.J.: Rutgers University Press, 2001. Greenwood, N. N., and A. Earnshaw. “Germanium, Tin, and Lead.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997. Guilbert, John M., and Charles F. Park, Jr. The Geology of Ore Deposits. Long Grove, Ill.: Waveland Press, 2007. Massey, A. G. “Group 14: Carbon, Silicon, Germa- nium, Tin, and Lead.” In Main Group Chemistry.2d ed. New York: Wiley, 2000. National Research Council. Lead in the Human Envi- ronment: A Report. Washington, D.C.: National Academy of Sciences, 1980. Nriagu, Jerome O. Lead and Lead Poisoning in Antiq- uity. New York: Wiley, 1983. Warren, Christian. Brush with Death: A Social History of Lead Poisoning. Baltimore: Johns Hopkins Univer - sity Press, 2000. 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 Lead: Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/lead See also: Air pollution and air pollution control; Metals and metallurgy; Mineral resource use, early history of; Recycling; Silver; United States; Zinc. Leopold, Aldo Category: People Born: January 11, 1887; Burlington, Iowa Died: April 21, 1948; near Baraboo, Sauk County, Wisconsin In his years of government service and private work, Leopold was active in game management and wildlife preservation. His Sand County Almanac was influ- ential withsucceeding generationsof conservationists. Biographical Background Aldo Leopold, born in Burlington, Iowa, graduated from the Yale Forest School (now the Yale School of Forestry and Environmental Studies) in 1906. In 1909, after completing his master’s degree, he joined the U.S. Forest Service and fostered the ecological poli- cies of Gifford Pinchot and Theodore Roosevelt. Sta- tioned in the southwestern United States, he advo- cated game conservation to avoid the erosion of sport hunting. He also helped establish a 200,000-hectare roadless wilderness in the Gila National Forest. While pursuing wolf eradication to ensure deer viability, he realized the importance of ecological interactions. Impact on Resource Use Leopold moved to Wisconsin in 1924, joined the U.S. Forest Products Laboratory, and developed the policy of wildlife management. He published Game Manage - ment, subsequently retitled Wildlife Management,in 1933. Inthe sameyear, hejoined the Universityof Wis - 692 • Leopold, Aldo Global Resources consin at Madison Department of Agricultural Eco- nomics. He assisted Robert Marshall in creating the Wilderness Society in 1935, and he established a one- man Department of Wildlife Management in 1939. Leopold advocated integration of local concerns with universities, government agencies, and the pri- vate sector to balance farming, forestry, wildlife, and recreation. He escaped on the weekends to his sand farm in Wisconsin, where he wrote prolifically. His Sand County Almanac, published posthumously in 1949, represents a lifetime of observations concern- ing ecology, ethics, and aesthetics and concludes that a policy is right when it tends to preserve the integrity, stability, and beauty of the biotic community; any other policy, according to Leopold, is wrong. Aaron S. Pollak and Oliver B. Pollak See also: Conservation; Pinchot, Gifford; Roosevelt, Theodore; Wilderness; Wilderness Society. Lime Category: Mineral and other nonliving resources Where Found Lime is a manufactured product not found in nature. It is usually derived from the common sedimentary rocks limestone, dolomitic limestone, and dolostone, although it can also be produced from other high- calcium materials such as marble, aragonite, chalk, shell, and coral. Primary Uses An essential industrial chemical, lime is used in the manufacture ofsteel,pulp and paper, glassandporce- lain, and chemicals. It is a component of construction materials such as plaster, mortar, stucco, and white- wash. It is also used in conditioning acidic soils, soft- ening water, and treating wastewater and smokestack emissions. Technical Definition Lime (also known as quicklime, caustic lime, or calcia) is a common term for the chemical compound calcium oxide (CaO). The name is often applied to several related compounds, including hydrated or slaked lime (calcium hydroxide, Ca(OH) 2 ); dolomitic quicklime (CaO C MgO); type N (Ca(OH) 2 C MgO) and type S (Ca(OH) 2 C Mg(OH) 2 ) dolomitic hydrates; and refractory lime, also called dead-burned or hard- burned lime. When pure, lime occurs as colorless, cu- bic crystals or in a white microcrystalline form; often impurities such as iron and oxides of silicon, alumi- num, and magnesium are present. Lime has a specific gravity of 3.34, a melting point of 2,570° Celsius, and a boiling point of 2,850° Celsius. Description, Distribution, and Forms A highly reactive compound, lime combines with water to produce the more stable hydrated lime. This reaction, known as slaking, produces heat and causes the solid almost to double in volume. At temperatures around 1,650° Celsius, lime recrystallizes into the coarser, denser, and less reactive refractory lime. When heated to approximately 2,500° Celsius, lime is incan- descent. Lime is a highly reactive manufactured compound that is an essential part of many industrial processes. An alkali, it dissolves in water to produce a caustic, ba - Global Resources Lime • 693 Aldo Leopold’s seminal Sand County Almanac (1949) has influ- enced generations ofconservationists. (AP/Wide World Photos) sic solution. Lime is typically obtained from lime - stone, although other natural substances that are high in calcium are also used as raw materials for lime manufacture. Total world production of lime ap- proaches 300 million metric tons, about 20 million metric tons of which are produced in the United States (including Puerto Rico). From 2003 to 2007, the United States was second to Chinainlime produc- tion. History Use of lime in construction dates back at least to the ancient Egyptians, who, between 4000 and 2000 b.c.e., employed it as a mortar and plaster. The Greeks, Ro- mans, and Chinese used it in construction, agricul- ture, textile bleaching, and hide tanning. One of the oldest industries in the United States, lime manufac- ture began in colonial times. While the use of lime in- creased with the Industrial Revolution, it remained largely a construction material until the early twenti- eth century, when it became a crucial resource for the rapidly growing chemical industry. Obtaining Lime Lime may be prepared from a variety of naturally oc- curring materials with a high calcium content. While lime is commonly obtained from limestone, a sedi- mentary rock composed chiefly of calcite (calcium carbonate, CaCO 3 ), it can also be derived from dolo- stone, a similar sedimentary rock that is predomi- nantly dolomite (CaMg(CO 3 ) 2 ), or from rock with an intermediate composition (dolomitic limestone). Lime is also produced from marble, aragonite, chalk, shell, and coral (all mostly calcium carbonate). Be- cause the raw materials for lime manufacture are plentiful and widespread, lime is produced all over the world, with production facilities generally located near the sources for the raw materials. When calcium carbonate is heated in a masonry furnace to about 1,100° Celsius, it breaks down into lime and carbon dioxide. Heating dolomite in this fashion produces dolomitic quicklime and carbon di- oxide. Approximately 100 metric tons of pure lime- stone yields 56 metric tons of lime. Adding water to stabilize lime or dolomitic quicklime yields the hy- drated (slaked) form. Dolomite is typically used to make refractory (dead-burned) lime, which involves heating the materials to temperatures around 1,650° Celsius. Uses of Lime A fundamental industrial chemical, lime is used in the manufacture of porcelain and glass, pigments, pulp and paper, varnish, and baking powder. It is em- ployed in the preparation of calcium carbide, calcium cyanamide, calcium carbonate, and other chemicals; in the refining of salt and the purification of sugar; in treating industrial wastewater, sewage, and smoke- stack effluent; and in softening water. In metallurgy it is used in smelting and in concentrating ores. Lime and other calcium compounds are used in liming, a method for treating acidic soils. The application of lime to soil neutralizes acidity, improves soil texture and stability, and enriches the soil’s nitrogen content by increasing the activity of soil microorganisms that secure nitrogen from the air. Lime’s incandescing properties are employed in the Drummond Light, or limelight, in which a cylinder of lime is heated with the flame of an oxyhydrogen torch to produce a bril- liant white light. Mixed with sand and water, lime serves as a mortar or plaster. The lime hydrates in 694 • Lime Global Resources Chemical & industrial 23% Metallurgical 36% Construction 13% Environmental 28% Source: Historical Statistics for Mineral and Material Commodities in the United States Note: U.S. Geological Survey, 2005, lime statistics, in T. D. KellyandG.R.Matos,comps., ,U.S. Geological Survey Data Series 140. Available online at http://pubs.usgs.gov/ds/2005/140/. Miscellaneous “other” uses of 1% are included in the categories above. U.S. End Uses of Lime combination with water; the mortar hardens quickly as the hydrated lime reacts with carbon dioxide in the air to form calcium carbonate. Dolomitic quicklime is used to produce a hard, strong, and elastic stucco. Uses of hydrated lime include soil liming, sugar re- fining, and chemical preparation. In leather tanning, hydrated lime is used to remove hair from hides. In construction, it is used to increase the durability of mortar, plaster, and stucco. Hydrated lime in a highly dilute solution is whitewash. Filtering whitewash yields lime water, used in medicine as a burn treatment and as an antacid, and in chemistry as a reagent. Dolomitic hydrates are used as a flux in the manufac- ture of glass. Dead-burned lime is a refractory material, able to withstand contact with often corrosive substances at elevated temperatures. Refractory lime is a compo- nent in tar-bonded refractory brick, which is used in the construction of the basic oxygen furnaces em- ployed in steelmaking. Karen N. Kähler Further Reading Boggs, Sam. “Limestones.” In Petrology of Sedimentary Rocks. 2d ed. Cambridge, England: Cambridge University Press, 2009. Boynton, Robert S. Chemistry and Technology of Lime and Limestone. 2d ed. New York: Wiley, 1980. Jensen, Mead L., and Alan M. Bateman. Economic Min- eral Deposits. 3d ed. New York: Wiley, 1979. Kogel, Jessica Elzea, et al., eds. “Lime.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: Society for Mining, Metal- lurgy, and Exploration, 2006. Oates, J. A. H. Lime and Limestone: Chemistry and Tech- nology, Production and Uses. New York: Wiley-VCH, 1998. 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 Lime: Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/lime See also: Calcium compounds; China; Glass; Lime - stone; Metals and metallurgy; Oxides. Limestone Category: Mineral and other nonliving resources Limestone isone of the mostwidely used rockmaterials. It isused as roadmetal, asaggregate for macadamand concrete, and as a building stone. Definition Limestone is a widespread marine sedimentary rock found wherever shallow seas once encroached onto continents. Limestone accounts for 10 to 15 percent of all sedimentary rocks. Some limestones are formed in lakes, around springs, at geysers, and in caves. The term “limestone” encompasses many rocks of diverse appearance that have calcite as their essential compo- nent. They differ considerably in texture, color, struc- ture, and origin. Overview Although limestones may form by inorganic precipi- tation of calcite in lakes, springs, or caves, the most widespread limestones are of marine origin. Most limestones are formed by organic processes and con- sist largely of the shells and shell fragments of marine invertebrates. Because calcite is susceptible to solu- tion and recrystallization, diagenetic processes may completely alter the texture of the original rock. Limestone is a sedimentary rock composed largely of the mineral calcite (calcium carbonate). This rela- tively soft stone in its pure form is white, but it may be buff, pink, red, gray, or black, depending upon minor materials present. The texture ranges from fine- to coarse-grained and from highly porous to highly com- pact. Many limestones contain abundant fossils.Dolo- stone is a closely related rock composed primarily of dolomite (calcium-magnesium carbonate). Coquina is a limestone of comparatively recent formation consisting of loosely cemented shell frag- ments. Compact rocks with abundant shell material are known as fossiliferous limestone. They may be de- scribed more specifically by adding the dominant fos- sil genera to the rock name. Chalk is a fine-grained, porous, white rock made up of minute tests of fo - raminifera. Lithographiclimestone isacompact, fine- Global Resources Limestone • 695 grained rock that is used in the printing process from which it derives its name. Travertine is an inorganic deposit usually formed in caves as coarse, crystalline dripstone. Tufa is a porous, spongy material depos- ited around springs and geysers. Oolitic limestone is composed of small, spherical bodies of concentrically layered calciteformed in shallowwaterwith moderate agitation. Coarse crystalline limestone forms by re- crystallization of primary, fine-grained limestones. Limestone andother solublerocks in warm, humid regions are susceptible to solution by meteoric water at the surface and in the subsurface. The resulting landscapes, characterized by abundant sinkholes and caverns, are known as karst topography. Because water moves rapidly into the subsurface in karst regions, rapid spreading of contamination in groundwater is of special concern. Some limestones that take a good polish are mar - keted as marble. Limestone is used as a flux in open- hearth iron smelters. It is a basic raw material in the manufacture of portland cement. It is also used as an inert ingredient in pharmaceutical preparations. Limestone is the chief source of chemical and agricul- tural lime.It is alsoground and pressedto make black- board chalk. Limestone serves as a significant aquifer, and it constitutes about 50 percent of reservoir rocks for oil and gas. Prior to the introduction of electric lighting, carved chunks of limestone were fed into a gas flame to produce a fairly bright light used as stage lighting—hence the term “limelight.” René A. De Hon Further Reading Boggs, Sam. “Limestones.” In Petrology of Sedimentary Rocks. 2d ed. Cambridge, England: Cambridge University Press, 2009. Boynton, Robert S. Chemistry and Technology of Lime and Limestone. 2d ed. New York: Wiley, 1980. Kogel, Jessica Elzea, et al., eds. “Lime.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses. 696 • Limestone Global Resources Lower magnesian limestone in Dane County, Wisconsin. (USGS) 7th ed. Littleton, Colo.: Society for Mining, Metal - lurgy, and Exploration, 2006. Oates, J. A. H. Lime and Limestone: Chemistry and Tech- nology, Production and Uses. New York: Wiley-VCH, 1998. 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 Lime: Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/lime See also: Aggregates; Carbonate minerals; Cement and concrete; Groundwater; Marble; Oil and natural gas reservoirs; Quarrying. Lithium Category: Mineral and other nonliving resources Where Found Lithium makes up about 0.006 percent of the Earth’s crust and is found as a trace element in most rocks. The most important lithium ore is spodumene, with extensive deposits in North Caro- lina, Canada (Quebec), Brazil, Argen- tina, Spain,and theDemocratic Repub- lic of the Congo. Another important commercial source of lithium is lepido- lite. Primary Uses In combination with other metals, lith- ium is used as a heat exchanger in nu- clear reactors as well as a radiation shield around reactors. Lithium is used as an anode in high-voltage batteries, and lithium compoundsare used in the manufacture of rubber products, ce - ramic products, enamels, dyes, glass, and high-temperature lubricants. Technical Definition Lithium, symbol Li, is located in Group IA of the peri- odic table.It has anatomic number of3 and anatomic weight of 6.941. It is a soft, silvery-white metal and is the lightest known metal. It has a melting point of 180.54° Celsius, a boiling point of 1,347° Celsius, a specific gravity of 0.534, and a specific heat of 0.79 cal- orie per gram per degree Celsius. Description, Distribution, and Forms Lithium quickly becomes covered with a gray oxida- tion layerwhen it isexposed to air, andbecauseit com- bines so easily with other elements, lithium is always found chemically bonded in nature. Although a highly reactive element, lithium is less reactive than the other alkali metals. Like the other alkali metals, it easily gives up an electron to form monovalent positive ions. History Lithium wasdiscovered by Swedish industrialistJohan August Arfwedson in 1817. The element was first iso- lated in 1818 by Sir Humphry Davy through electro- lytic reduction of the lithium ion. Global Resources Lithium • 697 Batteries 25% Ceramics &glass 18% Lubricating greases 12% Pharmaceuticals & polymers 7% Air conditioning 6% Other 32% Source: Mineral Commodity Summaries, 2009 Note: Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009. “Other” includes primary aluminum production, continuous casting, chemical processing, and other uses. Global End Uses of Lithium . history is usually a function of the technology and economics of the time; many of these ores were particularly rich by modern standards. Silver was critical to maintenance of the Roman financial system,. content of the ore ranges between 5 and 10 percent— are depleted. This type of “exhaus- tion” of a deposit is a function of the prevailing technology and eco- nomics. In the first half of the. Management,in 1933. Inthe sameyear, hejoined the Universityof Wis - 692 • Leopold, Aldo Global Resources consin at Madison Department of Agricultural Eco- nomics. He assisted Robert Marshall in