of alternative energy schemes (Exxon, for example, invested $5 billion in its oil-from-shale project in Col- ony, Colorado) and the acquisition of holdings in such other energy sectors as coal and uranium. These companies would do much the same vis-à-vis biofuels in the high-cost-petroleum era that followed the U.S. invasion of Iraq in 2003. The downturn in the price of oil in the 1980’s caused the majors to shut down most of their alterna- tive energy projects and toseekmeans for surviving in the lean yearsof the global recession. Asthese compa- nies would do in even more publicized ventures dur- ing the 1990’s, when the price of oil remained in the twenty-five-dollar-per-barrel range, many turned to mergers in order to economize, beginning with the 1984 merger between SoCal and Gulf Oil that enabled Gulf to sell off many of its subsidiaries and service sta- tions and led SoCal to change its name to Chevron. A decade later, what had been exceptional in 1984 be- came, momentarily, almost commonplace. The pro- cess began in December, 1998, when BritishPetroleum (BP) acquired Amoco (formerly the American Oil Company or Standard Oil of Indiana) for more than $50 billion. The following year the combined corpo- ration purchased ARCO (one of the major players in the discovery of Alaskan oil). Combined with its sub- sequent acquisition of Burmah Castrol, a lubricant manufacturing company, BP was abletopare approxi- mately twenty thousand jobs worldwide and become temporarily the world’s largest oil company. BP held that distinction for only a few months, until Exxon and MobilmergedinNovember, 1999, into the largest corporation in the world. The transaction en- abled the combined corporation to sell off more than seventeen hundred service stations (to Tosco) and trim its payroll by nearly ten thousand employees. The merger mania did not end there, or on the United States side oftheAtlantic Ocean. In 1999,twogiant Eu- ropean petroleum firms, France’s Total and Belgium’s Petrofina, merged into TotalFina, and then acquired France’s other major petroleum company, Elf,to make TotalFina the fourth largest petroleum company inthe world. Then, in 2001, another Sister-Sister marriage occurred, this time involving Chevron and Texaco. In short, by the time oil prices began to rise appre- ciably shortly after the terrorist attack on New York and Washington, D.C., on September 11, 2001, and especially following the U.S. invasion of Iraq in 2003, a new set of six “supermajors” had emerged in the world of private oil companies: Exxon-Mobil, BP- Amoco, Chevron-Texaco, TotalFina, Royal Dutch Shell, and Conoco-Phillips (whose two units com- pleted their merger inAugust,2002).Allarevertically integrated and, compared to the “independents,” they have a commandingshareofthemarket.Unlikethatof the Seven Sisters, though,theirpowerisrooted in sales, not the production of oil,in which they accounted for only approximately 10 percent of the oil produced in the early years of the twenty-first century, and cer- tainly not in ownership of oil and gas, for which their combined ownership accounts for less than 5 percent of the world’s known oil and gas reserves. State-Owned Petroleum Industries Comparatively speaking, the real “supermajors” are not these private oil companies but the seven largest state-owned petroleum companies in the contempo- rary world, led by those of Saudi Arabia, Iran, Russia, and Venezuela, but also including the state-owned companies of China, Brazil, and Malaysia. Collectively, these seven account for nearly one-third of the world’s gas and oil production and the majority of its known oil reserves. More important, when combined with the production capacity and reserveholdingsofother state-owned oil companies,theseactorsaccountforthe overwhelming majority of the world’s oil and gas pro- duction and reserves. In that sense they are more anal- ogous to the Seven Sisters than today’s “supermajor” private oil corporations. However, unlike the Seven Sisters, they do not collaborate with one another. Quite to the contrary, they sometimes compete with one another for influence inside OPEC (where only Saudi Arabia, Iran, and Venezuela are represented) and forprofitsintheworld’s petroleum marketplace. Joseph R. Rudolph, Jr. Further Reading Davis, David Howard.Energy Politics. 4thed. New York: St. Martin’s Press, 1993. Deffeyes, Kenneth. Hubbert’s Peak: The Impending World Oil Shortage. Rev. ed. Princeton, N.J.: Prince- ton University Press, 2003. Falola, Toyin, and Ann Genova. The PoliticsoftheGlobal Oil Industry: An Introduction. Westport, Conn.: Praeger, 2005. Grace, Robert. Oil: An Overview of the Petroleum Indus- try. 6th ed. Houston, Tex.: Gulf, 2007. Paul, William Henry. Future Energy: How the New Oil In - dustry Will Change People, Politics, and Portfolios. Hoboken, N.J.: John Wiley and Sons, 2007. 878 • Oil industry Global Resources Priest, Tyler.The Offshore Imperative: Shell Oil’sSearch for Petroleum in Postwar America. College Station: Texas A&M University Press, 2007. Rees, Judith, and Peter Odell, eds. The International Oil Industry: An Interdisciplinary Perspective. New York: St. Martin’s Press, 1987. Sampson, Anthony. TheSeven Sisters: The Great OilCom- panies and the World They Shaped. New York: Viking Press, 1975. Simmons, Matthew B. Twilight in the Desert: The Coming Saudi Oil Shock and the World Economy. Hoboken, N.J.: John Wiley and Sons, 2005. Solberg, Carl. Oil Power: TheRiseandImminentFallofan American Empire? New York: New American Library, 1976. Yeomans, Matthew. Oil: Anatomy of an Industry. New York: New Press, 2004. Yergin, Daniel. The Prize: The Epic Quest for Oil, Money, and Power. New ed.NewYork: The Free Press,2008. See also: Energy politics; Getty, J. Paul; Oil and natu- ral gas exploration; Oil embargo and energy crises of 1973 and 1979;Organization of Petroleum Exporting Countries; Peak oil; Resources as a medium of eco- nomic exchange; Resources as a source of interna- tional conflict; Rockefeller, John D.; Saudi Arabia; United States; Venezuela. Oil shale and tar sands Category: Energy resources Oil shale and tar sands are sources of oil and gas fuel, lubricants, and chemical feedstock. Tar sands are rocks with pore spaces filled by solid or semisolid bitu- men. Oil shale is any fine-grained sedimentary rock containing kerogen and yielding petroleum when heated in the absence of oxygen. Background Tar sands are most abundant in sandstone and lime- stone. Most large depositsoccur near sedimentary ba- sin margins in deltaic, estuarine, or freshwater rocks. Oil shale occurs inlacustrine (lake) sediments, associ- ated with coal, or in marine shale. Kerogen is a waxy, insoluble organic compound with a large molecular structure. Almost all sedimen - tary rocks contain somekerogen; those thatboth con - tain kerogen and yielda few liters ofoil per metric ton are considered oil shale. About 45 liters per metric ton generally is the minimumfigure used for calculat- ing reserves. Ninety to 135 liters are required for de- velopment. Some shales contain more than 225 liters per metric ton. Worldwide shale oil resources have been estimated at 3 trillion barrels, of which the United States has 2 trillion. Origin of Oil Shale Oil shale forms in oxygen-deficient environments where organic debris accumulates more rapidly than it is destroyed by oxidation, scavengers, or decay. Deep, confined ocean basins with stagnant water or restricted water circulation may preserve organic de- bris. Baltic and Manchurian oil shales are of this ori- gin. Swamp lakes, with slow circulation and rapid ac- cumulation of plant debris, also may produce oil shale. Oil shale accompanying coal in Scotland and North America are examples. Lakes with noncircu- lating water at the bottom also may accumulate oil shale. The gigantic Green River oil shale deposit of Wyoming and Colorado is of this type. Producing Oil Shale Very great amounts of shale are needed for economi- cally significant petroleum production. Open-pit mining is much more economical than underground mining, although there are some large underground mines. Pits 300 meters deep and 3 kilometers across have costs equal to those of underground mining in the Green River deposit. Further expansion reduces expense, making gigantic pits the most economical mining option. Heating shale in the absence of oxy- gen (retorting) converts kerogen (solid organic mate- rial that is insoluble in petroleum solvents) to liquids. The liquid then requires hydrogenation to make pe- troleum. Retorted shale is saline and/or alkalic powder. Open pits are ready disposal sites for waste material, and underground mines may be backfilled. The re- maining 10 percent or more of retort waste, however, requires disposal elsewhere. Finally, thewaste must be isolated from surface water and groundwater to pre- vent contamination. In situ processing solves some disposal problems. In this method large blocks of oil shale are undermined and collapsed, creating an un- derground porous rubble. Gas introduced to the top of the rubble is ignited,afterwhichtheshaleburns on its own. Gas and oil “cooked” from the rock are with - Global Resources Oil shale and tar sands • 879 drawn from the base of the rubble, leaving the spent shale underground. Shale Oil History Shale oil for medicinal purposes was produced in 1350 at Seefeld, Austria. The manufacture of illumi- nating oil and lubricants from oil shale began in France around 1830 and quickly spread through Eu- rope and North America. Petroleum almost entirely supplanted shale oil during the late nineteenth cen- tury. Afterward, shale oil production was largely lim- ited to periods of oil shortage or of military or eco- nomic blockade. Flammable oil shale, rich in kerogen, has been burned to generate steam in Latvia. Scot- land, the former Soviet Union, Manchuria, Sweden, France, Germany, South Africa, the United States, Brazil, and Australia all have produced shale oil, but total world production through 1961 was only about 400 million barrels. Tar Sand Occurrence Tar sand bitumens are larger, heavier, and more com- plex hydrocarbon compounds than those in liquid petroleum, and they include substantial nitrogen and sulfur. (“Bitumen” is a term for a very thick, natural semisolid material such as asphalt or tar.) Deposits are most abundant in sandstone or limestone. Most large deposits are in deltaic, estuarine, or freshwater sand- stone. The largest occur at depths of less than 1,000 meters on sedimentary basin margins where inclined layers of petroliferous rocks approach the surface. Here, upward migrating petroleum could lose vola- tiles and,with oxygenation and biodegradation, leave asphalt-impregnated rock. Some solid bitumens may be hydrocarbons not yet sufficiently altered to form liquids rather than residues of once liquid material. United States reserves, although large, are insignif- icant compared to those of Canada and Venezuela. Additional deposits are known in Albania, Siberia, Madagascar, Azerbaijan, the Philippines, and Bul- garia. Tar Sand History Tar sands have been used since ancient times for sur- facing roads, layingmasonry, and waterproofing. The Athabasca tar sand deposit of northern Alberta, Can- ada, was discovered in 1778 when Peter Pond, a fur trader, waterproofed his canoes with tar. Geologic ex - ploration began in the 1890’s, and by 1915 tar sand was being shipped to Edmonton, Alberta, to pave streets. Pilot plant extraction of oil began in 1927. Af - terward, exploitation continued with provincial and federal subsidies and support. By the end of the twen- tieth century, operations were self-supporting. Tar Sand Exploitation Canadian tar sand is mined in large open pits and transported to processing plants where steam treat- ment produces bitumen froth and sand slurry. Naph- tha steam removes the remaining sand, leaving viscous bitumen. Raw bitumen then is “cracked,” a chemical process by which the large organic mole- cules in the bitumen are broken into smaller, more liquid molecules, gas, and coke. Finally, cracked oil is hydrogenated to produce synthetic crude oil. Sulfur is a salable by-product. Sand ultimately is returned to the pit, overburden is replaced, and the site is re- forested. Open-pit production, however, is feasible only at the shallow periphery of the deposit, so in situ extrac- tion will berequired for about90percent of the Cana- dian deposit. In one system, wells drilled into the de- posit are injected with steam to liquefy the bitumen. Bitumen then is pumped until flow ceases, after which the well is again steamed. In another system wells sunk into the tar sand are ignited. Heat then cracks the bi- tumen, producing liquid and gas that flow to produc- tion wells. Ralph L. Langenheim, Jr. Further Reading Bartis, JamesT., et al.Oil Shale Development inthe United States: Prospects and Policy Issues. Santa Monica, Calif.: Rand Institute, 2005. Chastko, Paul. Developing Alberta’s Oil Sands: From Karl Clark to Kyoto. Calgary, Alta.: University of Calgary Press, 2004. Clarke, Tony. Tar Sands Showdown: Canada and the New Politics of Oil in an Age of Climate Change. Toronto: J. Lorimer, 2008. Meyer, Richard F., ed. Exploration for Heavy Crude Oil and Natural Bitumen: Research Conference. Tulsa, Okla.: American Association of Petroleum Geolo- gists, 1987. Nikiforuk, Andrew. Tar Sands: Dirty Oil and the Future of a Continent. Vancouver, B.C.: Greystone Books, 2009. Rühl, Walter. Tar (ExtraHeavy Oil) Sands andOil Shales. Stuttgart, Germany: Enke, 1982. Russell, Paul L. Oil Shales of the World: Their Origin, Oc - 880 • Oil shale and tar sands Global Resources currence, and Exploitation. New York: Pergamon Press, 1990. Selley, Richard C. Elements of Petroleum Geology.2ded. San Diego, Calif.: Academic Press, 1998. Welles, Chris. The Elusive Bonanza: The Story of Oil Shale—America’s Richest and Most Neglected Natural Resource. New York: Dutton, 1970. Web Sites U.S. Department of the Interior, Bureau of Land Management About Oil Shale http://ostseis.anl.gov/guide/oilshale/index.cfm U.S. Department of the Interior, Bureau of Land Management About Tar Sands http://ostseis.anl.gov/guide/tarsands/index.cfm U.S. Geological Survey Heavy Oil and Natural Bitumen: Strategic Petroleum Reserves http://pubs.usgs.gov/fs/fs070-03/fs070-03.pdf U.S. Geological Survey Natural Bitumen Resources of the United States http://pubs.usgs.gov/fs/2006/3133/pdf/FS2006- 3133_508.pdf See also: Athabasca oil sands; Energy economics; Mining wastes and mine reclamation; Oil and natural gas formation; Open-pit mining; Strip mining. Oil spills Category: Pollution and waste disposal Major oil spills can be environmentally devastating. Not all spills are catastrophic, however, and a number of techniques have been developed to contain and clean up the oil; a spill’s locationisthesinglemostimportant factor in the amount of damage it causes. Background The world’s oil reserves are developed by drilling, a process that brings oil to the surface, where it can be stored temporarily in tanks until transportation by pipeline or oil tanker. The oil is then transported: Pipelines move oil long distances across land, while tankers carry oil across the oceans. Transported oil is delivered to refineries, where it is separated into various useful components, including gasoline, jet fuel, home heating oil, diesel fuel, and lubricants. These refined products are shipped to storage facili- ties where they await delivery. The drilling, storage, and transportation of oil sometimes result in the accidental release of oil into the natural environment. Even with improvements in technology and safety, accidental spills are inevitable because of theunpredictable natures of human error, faulty equipment, and weather. During the drilling of a well, oilcansurgeupwardtothesurface and spill out into the environment, an event referred to as a “blow- out.” Oil storage tanks can leak oil through a faulty valve or through a valve accidentally left open. Oil transported by pipeline can escape into the environ- ment if the pipeline isaccidentallyruptured. Oil tank- ers canspill oil into the oceanafter grounding during severe weather. The Fate of Spilled Oil Oil spilled onto the ground generally soaks into the soil and does not spread far from the source of the spill. Large populations of soil bacteria eventually de- grade most of the oil. Oil spilled into water, however, spreads over the surface into a thin film. After spread- ing, the oil coversalargeareafarawayfrom the source of the spill. Once on the water’s surface, oil is subjected to a se- quence of weatheringprocesses. Volatile components in the oil are rapidly lost to the atmosphere. Ultravio- let radiation in sunlight breaks down some oil com- ponents in a process called photooxidation. Water- soluble components of oil dissolve into the water. Oil remaining on the surface begins to break up into small droplets that enter the water, a process aided by high winds and waves. Water turbulence at the surface can mix oil and water together into a mixture called a mousse. In the water, oil collects suspended particles, and this mixture eventually sinks to the bottom. Bot- tom oil is rolled along by water currents while collect- ing more oil and particles. Eventually, bottom oil is buried or washed ashore. Oil that remains in the natural environment for any length of time is subjected to the natural process of biodegradation. The bacteria that carry out this process are widespread in the environment. These or - ganisms use the oil as anutrient source to grow. In the process, they degrade the chemical components of Global Resources Oil spills • 881 the oil into harmless end products. This process, if given sufficient time, can remove the majority of spilled oil from the natural environment. Oil Cleanup Techniques Oil spilled on the ground can be soaked up with straw or commercially available oilsorbents. The oil-soaked materials can then be disposed of by burning or burial. Oil spilled into water presents a far greater challenge to clean up,since it can quickly spread over a large area. Since spilled oil spreads quickly, a rapid response is essential. The flow of oil into the environ- ment must be stopped, and the spread of spilled oil must be minimized. Oil containment booms are often used to stop the spread of oil across water. Booms are placed around the source of thespill in an effort to re- strict oil to a small area where it can be picked up by skimmers. Skimmers dip a belt into the water to pick up oil from the surface andthenscrapethebeltacross a roller to remove the oil. The oil scraped off the belt falls into a storage tank. Oil that has escaped to cover large areas of water surface canbe removed bythe use ofchemical disper- sants. Dispersants break up theoil into tiny droplets that readily mix into thewater.Oil that has beenmixedinto the water is less likely to strand along the shoreline. Oil that strands on the shoreline can be difficult to remove. Shoreline cleanup of sandy beaches is often labor-intensive and employs rakes, shovels, and sorbents to remove oil. Rocky shorelines can some- times be cleaned safely by low-pressure water spray- ing, but high-pressure spraying can be harmful. Cer- tain shoreline types, like marshes, are particularly sensitive to disturbance and should be left alone. One of the more effective tools to emerge for the cleanup of oiled shorelines is bioremediation. This method relies on the natural ability of bacteria in the environment to break down oil. In bioremediation, natural breakdown is stimulated by the addition of a fertilizer to the shoreline because the natural process is often limited by a lack of nutrients. With the addi- tion of nutrients to the fertilizer, oil biodegradation occurs at an accelerated rate. This technique was used successfully on the shorelines of Prince William Sound after the Exxon Valdez oil spill. Environmental Effects of Oil Spills Pictures of dead and dying animals are often used to depict the biological damage that oil spills can cause. The effects of major spills are indeed devastat - ing. The effects of smaller spills—or of spills in the open ocean—are significantly less severe. The degree of damage varies with a number of factors, including the type of oil spilled, the amount of oil spilled, and the location of the spill. Spill location is perhaps the single most important factor. Spillsthat occur in open water areas, such ascoastal seas, typically have lessbio- logical impact than thosethatoccurin enclosed water areas, such as bays and sounds. A comparison of the biological damage after the 1969 Santa Barbara oil spill and the 1989 Exxon Valdez oil spill will illustrate this point. The Santa Barbara oil spill occurred in the Santa Barbara Channel off the coast of California. A total of 69,000 barrels of oil was released as a result of a well blowout. The oil spread over a large area of coastal seas and weathered for a period of seven days before portions began to strand on shorelines. Only a frac- tion of the spilled oil eventually came ashore along beaches and rocky shores. Theoil caused thedeath of shore animals, seabirds, and marine mammals, but mortality was neither widespread nor extensive be- cause ofthepriorweatheringanddispersaloftheoil. The Exxon Valdez oil spill occurred in Prince Wil- liam Sound, Alaska, in 1989. The tanker Exxon Valdez ruptured its oil storage tanks after grounding on Bligh Reef. Ruptured tanksreleased a total of 264,200 barrels of oil into the enclosed waters of Prince Wil- liam Sound. The spilled oil didnot weather or disperse prior to its spread across 28,500 square kilometers of enclosed water and 1,900 kilometers of adjacent shoreline. Therefore, the death of shoreline animals was widespread and extensive, as was the death of sea- birds and marine mammals. An estimated 250,000 to 500,000 seabirds died as a result of the spill, in addi- tion to an estimated 4,000 to 6,000 marine mammals. Oil was stillfound buried beneath thesurface ofsome shorelines four years after the spill. Steve K. Alexander Further Reading Easton, Robert. Black Tide: The Santa Barbara Oil Spill and Its Consequences. New York: Delacorte Press, 1972. El-Nemr, Ahmed. Petroleum Contamination in Warm and Cold Marine Environments. New York: Novinka Books, 2006. Fingas, Merv. The Basics of Oil Spill Cleanup.2ded. Edited by Jennifer Charles. Boca Raton, Fla.: Lewis, 2001. 882 • Oil spills Global Resources Holleman, Marybeth. The Heart of the Sound: An Alas - kan Paradise Found and Nearly Lost. Salt Lake City: University of Utah Press, 2004. Loughlin, Thomas R., ed. Marine Mammals and the Ex- xon Valdez.SanDiego,Calif.:AcademicPress, 1994. National Research Council. Oil in the Sea III: Inputs, Fates, and Effects. Washington, D.C.: National Acad- emy Press, 2003. _______. Oil Spill Dispersants: Efficacy and Effects. Wash- ington, D.C.: National Academies Press, 2005. Ott, Riki.Not One Drop: Betrayal and Courage in the Wake of the Exxon Valdez Oil Spill. White River Junction, Vt.: Chelsea Green, 2008. Web Site National Oceanic and Atmospheric Administration, National Ocean Service, Office of Response and Restoration Exxon Valdez Oil Spill http://response.restoration.noaa.gov/exxonvaldez See also: Alaska pipeline; American Petroleum Insti- tute; Biotechnology; Environmental biotechnology; Exxon Valdez oil spill; Oil and natural gas drilling and wells; Oil industry; Petroleum refining and process- ing; Water pollution and water pollution control. Olivine Category: Mineral and other nonliving resources Where Found Olivine is common in the Earth’s crust. Large depos- its of olivine are often associated with certain volca- noes. Primary Uses The main use of olivine is the use of peridot as a gem- stone, which is found in Arizona and on the Red Sea island of Zebirget. Through chemical reaction, it is also an energy source. Technical Definition Olivine generally appears in a variety of yellowish- green and yellowish-brown colors, depending on its specific chemical composition. It has a hardness of 6.5 to 7 on the Mohsscale.Thenameolivine refers to a se - ries of high-temperature minerals that have the end members forsterite (Mg 2 SiO 4 ) and fayalite (Fe 2 SiO 4 ). When the twoare chemically combined theyform the magnesium iron silicate that is commonly called oliv- ine. The higher-temperature member, forsterite, is rich in the element magnesium. Description, Distribution, and Forms Olivine is the group name for a series of minerals that have the end members forsterite and fayalite. The ol- ivine group of minerals is one of the more important rock-forming minerals that make uptheEarth’s crust. It is a high-temperature mineral group that is often associated with the volcanic rock basalt. It is a com- mon mineral in the rocks that constitute the Earth’s lower crust and upper mantle. Olivine is also one of the essential minerals found in the stony variety of meteorites. Olivine often occurs as attractive crystals. In color, olivine can appear with differing shades of yellowish- green. Depending upon its specific chemical compo- sition, olivine can also appear in shades of yellowish- brown to an almost reddish color. History Forsterite wasnamed after Johann R. Forster, an eigh- teenth century German naturalist who sailed with the English explorer Captain James Cook. Fayalite, the lower-temperature end member of the series, is rich in iron. It was named after the island Fayal in the Azores, where it is abundant. Obtaining Olivine Since olivine is a high-temperature mineral, it is usu- ally absent from the Earth’s surface. Large deposits of olivine are often associated with certain volcanoes. An unusually explosive volcano can rapidly transport olivine up from great depths and then expel it as it erupts. Lavas produced by such volcanoes often have numerous individual olivine crystals scattered throughout; thecrystals may also clump together and form as nodules. In both cases these crystals were forming within the magma at depth and were then transported upwardwith the rising magma. Whenthe magma eventually flowed out of the volcano as lava, it contained the olivine that originally formed at great depth. Associated with these eruptions are other rocks called xenoliths, which also formed at depth; they contain olivine as one of their principal minerals. This kind of rock is called periodite. Global Resources Olivine • 883 Uses of Olivine Peridot is the variety of olivine that is used as a gem- stone. It is somewhat transparent and ranges in color from a yellowish-green to olive green. The dark yellow- green stones are considered to be the most valuable. Flawless peridot is common, and it can be faceted in many different ways. Fine-quality peridot comes from the San Carlos Indian Reservation in Arizona. The most sought-after stones come from the island of Zebirget in the Red Sea. Peridot is the birthstone for the month of August. Paul P. Sipiera Web Sites Natural Resources Canada Canadian Minerals Yearbook, 2005: Magnesium http://www.nrcan.gc.ca/smm-mms/busi-indu/cmy- amc/content/2005/36.pdf U.S. Geological Survey Mineral Information: Magnesium Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/magnesium/ See also: Gems; Igneous processes, rocks, and min- eral deposits; Iron; Magma crystallization; Magne- sium; Minerals, structure and physical properties of; Mohs hardness scale; Silicates; Silicon; Volcanoes. Open-pit mining Category: Obtaining and using resources Open-pit mining refers to the removal of mineral re- sources from the Earth without the use of either tunnels or wells. A gravel pit represents the simplest example of an open-pit mine. Although some mining engineers distinguish between strip mining and open-pit min- ing, the methods employed in both are similar. The ma- jor difference is that strip mines are generally shallow, while a pit may eventually descend to hundreds of me- ters below the original surface of the Earth. Background Open-pit mining is themethodmineowners prefer to use when the mineral body lies close enough to the surface of the Earth to allow the removal of the ore in continuous layers. It is both the safest and most eco - nomical methodofextractingmineralresources from a site. It has beenestimatedthatworldwide 70 percent of all minerals mined are obtained through open-pit mining processes. There is a strong economic incen- tive for mine operators to use the open-pit method. Mining by the open-pit method allows the mining company to extract 100 percent of the ore-bearing rock. In underground mines using tunnels and shaft- ing, the recovery rate of ore-bearing rock is generally 60 percent or less. Open-pit mining is also consider- ably safer than underground mining, as the ore is re- moved with power shovels and large trucks. Although underground mining also uses mechanized equip- ment, the workers are still exposed to risks such as cave-ins and explosions not present in open pits. Methods A few minerals are soft enough to be mined without the use of explosives. More commonly, mining pro- ceeds through a seriesof drilling holes, placing explo- sive charges in the holes and blasting, and then re- moving the shattered rock with extremely large power shovels and trucks. Most equipment used in open-pit mining is gargantuan in size. Power shovels, excava- tors, and draglines are custom-assembled at the mine since they are too large to transport other than in pieces. In the past, when a mine closed, this equip- ment was abandoned at thesite.Today itismore likely to be salvaged as scrap metal. In a few former mining districts, specialized equipment has been left in place and preserved as part of historic landmarks. In some cases the ore body lies close enough to the surface that mining begins directly. More often, a layer of waste material known as the overburden must be removed before the ore itself is exposed. The over- burden consists of the topsoilandunderlyingdirt and rock that contains no extractable ore. When mining begins, the layer of topsoil will be removed carefully and piled separately from other waste material, as the topsoil will be needed for use in the restoration pro- cess when the mine site is exhausted. Depending on the mine site, the type ofore mined, and other factors, the mining may proceed in parallel strips or may be done in a circular pattern that gradu- ally expands in diameter. Coal isoftenminedinstrips, as the mineral frequently occurs in layers that can cover a wide area but are only a meter or so in thick - ness. The mine operator removes the overburden from a strip of coal, excavates the coal, and then re - 884 • Open-pit mining Global Resources peats the process in a strip running next to the first strip. When the ore body is exhausted, the overbur- den will be backfilled into the stripped area as part of the restoration process. In the past, before legislation required mine operators to practice restoration, a strip-mined area often consisted of a devastated land- scape dominated by alternating trenches and ridges, with the land left unusable for either agriculture or wildlife habitat. Beginning with the passage of envi- ronmental regulations in the 1960’s, in the United States, strip-mined areas have been backfilled, lev- eled, and seeded with grass and trees. Metals such as iron are generally mined in pits that become both deeper and wider over time. The min- ing operation will commence as closely as possible to the known center of the site and expand bothout and down as ore is removed. Astimepasses,the pit may be - come surrounded by large piles of tailings, or waste rock. The final depth of the pit will be determined by factors such as the thickness of the ore body and the stability of thesurrounding walls of the pit. Apitdevel- oped to excavate material such as gravel often has walls composed of soft materials, such as a mixture of sand and gravel, and at risk of collapsing into the pit. Gravel pits therefore are generally quiteshallow. Even a pit mine for hard minerals, such as copper or iron, where the mineral is found in rock, may eventually reach a depth where the height of the walls makes it unsafe to dig the pit any deeper. If the ore is suffi- ciently valuable, mining of the remaining ore body may continue using shaft mining. In the past, large open-pit mines often operated next to or within communities, such as Butte, Mon - tana, and Bisbee, Arizona, both of which had enor - Global Resources Open-pit mining • 885 An open-pit mine in Kazakhstan. (Time & Life Pictures/Getty Images) mous copper mines. At one time the Anaconda opera- tion at Butte was reputed to be the largest open-pit mine in the world. As the mines expanded, homes and businesses were forced to relocate to accommodate the mine’soperation.Bytheendofthetwentiethcentury, however, the general public had grown less tolerant of mining. Property owners have sued mining compa- nies over quality-of-life issues such as noise pollution and dust.Developers now generally try to avoid open- ing new open-pit mines close to towns or suburbs. Environmental Issues Open-pit mining raises a number of obvious environ- mental protection questions. Even at its most innocu- ous, the mining process tends to be both noisy and dusty. Truck or rail traffic to and from the mine can create a nuisanceaswell as a safetyhazard for area res- idents. As the pit is deepened, it may affect the local water table. Water can seep into the pit, lowering the water table for the surrounding area, and can then present a hazard to local streams as it is pumped out loaded with sediment. Strip mining on hillsides can lead to erosion and contaminationbyminespillage of the local streams. Depending on the ore being mined, the open-pit mine may present potentially life-threatening prob - lems in addition to dust and noise. The mine itself may be relatively harmless, butprocessing plants built next to the mine to remove the ore from waste rock may involve the use of dangerous chemicals and pro- duce toxic by-products. Precious-metals mining can be particularly hazardous. In gold mining, for exam- ple, the ore oftenoccursin such small amounts within the ore body that remarkably large amounts of ore must be processed to obtain the precious metal using a method that employs cyanide and mercury. If these substances leak into the environment, they can poi- son streams and kill wildlife kilometers away from the mine itself. Iron ore mining can release sulfides into the environment, as can mining coal. Although not as toxic as cyanideand mercury, sulfides raise the acidity of water and can make lakes and streams uninhabit- able by aquatic life. In the United States, Canada, and many other na- tions, mine owners are now required by law to restore an open-pit mining site as closelyaspossibletoitsorig- inal condition. Toxic wastes must be removed or neu- tralized and the pit filled in. Restoration efforts at strip-mining sites in eastern states that enjoy a rela- tively wet climate, such as Tennessee and Ohio, have been successful. Phosphate mining areas in Tennes- see, for example, have been restored for use in agri- culture. Gravel pits and limestone quarries may be used as small wetlands. Water has always been prone to build up in abandoned pitmines.Engineeringcon - sulting firms exist that specialize in preparing aban - 886 • Open-pit mining Global Resources U.S. Bureau of Economic Analysis, , May, 2008.Source: Survey of Current Business $121.3 $225.7 $262.4 $275.8 Billions of Dollars 30025020015010050 2006 2000 2005 2007 Note: Includes oil and gas extraction, other mining, and support activities for mining. U.S. Gross Domestic Product in Mining, 2000-2007 doned pits to become wetlands and ponds. These firms clean up the site, slope the walls to make the pit safer, remove any potentially dangerous mining de- bris, and plant the species of vegetation most benefi- cial to wildlife nativetothe region. Restoration efforts in arid climates have been less successful. Lack of rain makes restoring native vegetation difficult and, even if tailings dumps and mine pits are bulldozed to less artificial contours, the scars from mining will be visi- ble for centuries. Nancy Farm Männikkö Further Reading Bell, Fred J., and Laurance J. Donnelly. “Quarrying and Surface Mining.”InMining and Its Impact on the Environment. New York: Taylor & Francis, 2006. Cameron, Eugene N. At the Crossroads: The Mineral Problems of the United States. New York: Wiley, 1986. Chinese Organizing Committee of the Fourteenth World Mining Congress, ed. Mining for the Future: Trends and Expectations. New York: Pergamon Press, 1990. Hartman, Howard L., and Jan M. Mutmansky. Intro- ductory Mining Engineering. 2d ed. Hoboken, N.J.: J. Wiley, 2002. Hustrulid, William, and Mark Kuchta. Open Pit Mine Planning and Design. 2d ed. New York: Taylor and Francis, 2006. Institution of Mining and Metallurgy. Surface Mining and Quarrying: Papers Presented at the Second Interna- tional Surface Mining and Quarrying Symposium. Lon- don: Author, 1983. Smith, Duane A. Mining America: The Industry and the Environment, 1800-1980. Lawrence: University Press of Kansas,1987. Reprint. Niwot: University Press of Colorado, 1993. Tatiya, Ratan Raj. Surface and Underground Excavations: Methods, Techniques, and Equipment. London: A. A. Balkema, 2005. Twitty, Eric. “The Technology of OpenPitMiningand Blasting.” In Blown to Bits in the Mine: A History of Mining and Explosives in the United States. Ouray, Colo.: Western Reflections, 2001. Web Sites Mine-Engineer.Com Open Pit Surface Mine http://www.mine-engineer.com/mining/ open_pit.htm U.S. Geological Survey Mining and Quarrying http://minerals.usgs.gov/minerals/pubs/ commodity/m&q See also: Mining wastes and mine reclamation; Quarrying; Strip mining; Underground mining. Ophiolites Category: Geological processes and formations Ophiolites are pieces of oceanic crust and upper mantle that have been thrust up on continental crust. They contain a wide range of minerals. Definition The process that forms ophiolites occurs where conti- nental crust is bent down and slips under oceanic crust, generally in a subduction zone. Ophiolites con- sist of a vertical sequence of (from bottom to top) mantle rocks, gabbro, sheeted dykes, and pillowed lavas. Ophiolites are remnants of ancient ocean bas- ins, demonstrating that an ocean basin once existed in the area and that plate convergence has destroyed the ocean basin. Ophiolites generally define and dec- orate suture zones, places where once-separated con- tinental blocks have collided. Ophiolites host a wide range of minerals, including chromite, platinum- group elements, and gold. Ophiolites are also impor- tant from a natural resources perspective because the tectonic forces that have put them in place often also form sedimentary basins that can contain fossil fuel deposits (oil, gas, and coal). Overview The term “ophiolite” comes from the Greek word ophis, meaning snake or serpent; the term’s origin is similar to that of the rock called “serpentinite.” Both terms refer to the mottled green (reptilian) appear- ance of these rocks. Ophiolites are sequences of oce- anic crust and uppermantlethathavebeen emplaced on continental crust by a process known as obduction. Obduction often faults, folds, and otherwise disrupts the original sequence of rocks. Nevertheless, ophio- lites provide the best-known example of the structure of oceanic crust. The typical ophiolite sequence is on the order of Global Resources Ophiolites • 887 . Channel off the coast of California. A total of 69,000 barrels of oil was released as a result of a well blowout. The oil spread over a large area of coastal seas and weathered for a period of seven. thickness of the ore body and the stability of thesurrounding walls of the pit. Apitdevel- oped to excavate material such as gravel often has walls composed of soft materials, such as a mixture of sand. they contain olivine as one of their principal minerals. This kind of rock is called periodite. Global Resources Olivine • 883 Uses of Olivine Peridot is the variety of olivine that is used as