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Limestone—A Crucial and Versatile Industrial Mineral Commodity

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Limestone—A Crucial and Versatile Industrial Mineral Commodity Limestone—A Crucial and Versatile Industrial Mineral Commodity imestone, as used by the minerals Lindustry, is any rock composed mostly of calcium carbonate (CaCO3). Although limestone is common in many parts of the United States, it is critically absent from some. Limestone is used to produce Portland cement, as aggregate in concrete and asphalt, and in an enormous array of other products, making it a truly versa- tile commodity. Portland cement is essential to the building industry, but despite our Nation’s abundance of limestone, there have been cement shortages in recent years. These have been caused in part by a need to find new areas suitable for quarrying oper- ations. To help manage our Nation’s Limestone is an essential mineral commodity of national importance. Some of the many prod- resources of such essential mineral ucts made using limestone are shown in this photograph—breakfast cereal, paint, calcium commodities, the U.S. Geological supplement pills, a marble tabletop, antacid tablets, high-quality paper, white roofing gran- Survey (USGS) provides crucial data ules, and Portland cement. (USGS photograph; use of trade, firm, or product names is for and scientific information to industry, descriptive purposes only and does not imply endorsement by the U.S. Government.) policymakers, and the public. other sea-dwelling creatures use these Earth’s surface. This process is called two chemicals to make protective shells “metamorphism.” There are also rare “igneous” carbonate rocks that have What is Limestone? by combining them to form calcite or “aragonite,” which is the same chemical crystallized from molten magma in the “Limestone” means any rock formed composition as calcite but has a different same way that lavas or granites have. mostly of calcium carbonate (CaCO3), crystal form. These are called “carbonatites,” and this but to geologists, limestone is only one Some limestones have been changed rock type is mined at a few places in the of several types of “carbonate rocks.” by the introduction of magnesium in world as industrial limestone. These rocks are composed of more ground water. Magnesium in ground Sedimentary limestone deposits than 50% carbonate minerals, generally water may convert some or all of the cal- can be extensive, covering hundreds the minerals calcite (pure CaCO3) or cite in the limestone to dolomite. Also, of square miles, and can be relatively dolomite (calcium-magnesium carbonate, some rocks formed near the shores of uniform in thickness and quality. There- CaMg[CO3]2) or both. ancient seas in arid climates were mostly fore, limestone quarries can be large Most carbonate rocks were depos- dolomite at the time they were deposited. and long lived, mining limestone layers ited from seawater. These sedimentary Limestone comes in many different that can be hundreds of feet thick over carbonate rocks are common on every varieties. Chalk is a very fine grained, areas of several square miles. Many continent and have formed through most porous marine limestone composed quarries produce multiple products, and of geologic history; they are still form- almost entirely of microscopic fossils. crushed rocks that are not pure enough ing today in the tropics as coral reefs and Travertine is a freshwater sedimentary for certain uses may still be suitable as at the bottoms of shallow seas. Marine limestone that has very thin, crenu- road aggregate. Marble quarries can limestone forms because seawater has lated layers and is commonly formed also be very large. However, these rocks high concentrations of two key dissolved at springs. Marble is a carbonate rock, that were once regularly bedded have chemicals—calcium (Ca++) and bicar- usually a marine limestone, that has been been metamorphosed into irregularly – bonate (HCO3 ) ions. In the near-surface squeezed and deformed like plastic by shaped bodies that are more difficult layer of most oceans, corals, clams, and great heat and pressure deep beneath the and costly to mine. U.S. Department of the Interior Fact Sheet 2008–3089 U.S. Geological Survey Revised August 2012 DISTANCE TO MARKETS AND SUITABLE QUARRY SITES AFFECT THE PRICE AND AVAILABILITY OF LIMESTONE In large parts of the United States there are extensive deposits of marine lime- stone. Most of the cost of limestone to the customer is determined by how far N away it comes from and how it is shipped. This aerial photograph shows the Antire Quarry in a rural setting near Eureka, Missouri. Interstate Highway 44 and the Burlington Northern and Sante Fe Rail- road are at the top right of the photo. The quarry is 25 miles southwest of central St. Louis, providing easy access to low-cost transportation and proximity to major markets. Other suitable quarry sites have been swallowed up by the city’s growth in recent years, resulting in “resource 0 1,000 feet sterilization.” (Photograph from Google- 0 400 meters Earth; used by permission of Bussen Quarries, Inc.) In large parts of the United States limestone is simply crushed and sieved applications. Most dolomite that is mined there are extensive deposits of marine for use in landscaping and roofing. is simply crushed and sieved for use as limestone of various ages from a few Powdered limestone is used to remove aggregate in concrete or asphalt. thousand to more than 350 million years impurities from molten metals like steel. old. Some deposits have chemical grades It can also remove toxic compounds from The Portland Cement Shortage as high as 95% CaCO . However, some the exhaust of coal-burning power plants. 3 Portland cement is one of the most areas are completely without any suitable Limestone is used as a filler in a variety important products made from limestone. limestone deposits. Most of the cost of of products, including paper, plastic, and It is essential in many construction appli- paint. The purest limestone is even used limestone to the customer is determined cations. The United States is not self-suf- in foods and medicines such as breakfast by how far away it comes from and how ficient in cement and must import it from cereals and calcium pills. it is shipped. Shipping by barge on water other countries to make up for shortfalls. Limestone is also the raw material for is cheaper than by train which, in turn, is Imports of clinker (the product from the making lime (CaO) that is used to treat cheaper than shipping by truck. first step in making cement) and finished soils, purify water, and smelt copper. cement accounted for about 23% of total Uses of Limestone Lime has many additional uses in the U.S. cement sales in 2006. In the years chemical industries. Limestone has many industrial uses just prior to 2007, Portland cement was Dolomites are commonly less suitable in seriously short supply in the Nation. and can be used as mined or processed than other industrial limestones for most into a wide variety of products. It is the Competition from other countries, an raw material for a large variety of con- inadequate ocean transport system, and struction, agricultural, environmental, underestimated cargo space requirements and industrial materials. were among the causes. Limestone is used in construction When Portland cement was in very almost everywhere. In 2007, crushed short supply, its price increased signifi- limestone was 68% of all crushed rock cantly. Consumers sought substitutes. They used pressure-treated wood, insu- produced in the United States. Also, lated steel, and polystyrene in panels, limestone is the key ingredient in making and even redesigned building footers to Portland cement. Despite our Nation’s reduce the amount of cement needed. abundance of limestone, there have been Cement shortages also caused construc- cement shortages in recent years. tion delays that resulted in increased Some of the purest of natural lime- costs for roads, bridges, and buildings. stones are marbles. For centuries, marble Many buildings in the Nation’s capital are has been the decorative stone of choice in Sources of Limestone in the Future government buildings and public statues. covered with limestone. The Apex Building/ Travertine is also used as a dimension Federal Trade Commission has an upper exte- Establishing new limestone quarries stone in tiles and tabletops. Some white rior of Indiana limestone. (USGS photograph) and cement plants in the United States is a slow process, and supply shortfalls U.S. crushed stone operations have vibration, and truck and other traffic associ- require time to correct. It takes about 2 been declining in number, about 20% loss ated with quarry operations. years to build a new cement plant, and per decade since 1971. However, from Some limestones are also aquifers, the permitting process can take much lon- 2001 through 2006, total annual U.S. lime- that is, they are rock units that can yield ger—8 to 10 years. Perhaps an even more stone production increased according to water to wells. Where limestone is an challenging problem is that people may U.S. Geological Survey (USGS) Mineral aquifer, there can be concerns that con- not welcome new quarries and plants Commodity Summaries, so the average taminants from the quarrying operations to their area. In spite of these obstacles, size of a quarry is increasing. In other could escape into the ground water. many U.S. cement companies are in the parts of the world, new production is com- In many areas of the United States process of expanding and modernizing ing mainly from a few very large quar- where limestone is found, it gradually their operations. ries. Despite increased U.S. production, dissolves in rainwater at the surface or in When an area of suitable and mine- the Nation was importing more and more the near-surface ground water. In humid able rock is swallowed up by urban of its limestone products until the recent climates, great volumes of limestone dis- growth or when mining becomes prohib- downturn in construction.
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