This category covers establishments primarily engaged in mining or quarrying dimension stone. Also included are establishments engaged in producing rough blocks and slabs. Establishments primarily engaged in mining dimension soapstone or in mining or quarrying and shaping grindstones, pulpstones, millstones, burrstones, and sharpening stones are classified in SIC 1499: Miscellaneous Nonmetallic Minerals, Except Fuels. Establishments primarily engaged in dressing (shaping, polishing, or otherwise finishing) blocks and slabs are classified in SIC 3281: Cut Stone and Stone Products. Nepheline syenite mining operations are classified in SIC 1459: Clay, Ceramic, and Refractory Minerals, Not Elsewhere Classified.
212311 (Dimension Stone Mining and Quarry)
In 2003, 132 U.S. companies produced 1.35 million tons of dimension stone for use in building, monuments, and curbing with a total value of $236 million. Roughly 176 quarries operated in 2003 in 34 states, with those in Indiana, Wisconsin, Georgia, Vermont, and Massachusetts accounting for 53 percent of the national output. Of the total industry tonnage, 34 percent was granite dimension stone, 28 percent limestone, 16 percent sandstone, 5 percent marble, 1 percent slate, and 16 percent other types of dimension stone.
The use of dimension stone in the high-end single-family housing sector was bolstered by an increase in residential construction in the early 2000s. Despite a weak U.S. economy, historically low interest rates fueled new housing starts. Increased use of granite and marble dimension stone in residential kitchens and bathrooms, limestone dimension stone in landscaping stone and ledges, and "worked" or hand-carved dimension stone and roofing slate in residential homes indicated that the residential segment would continue to be an expanding market for U.S. dimension stone producers.
The U.S. quarrying industry as a whole encompasses two major sectors: crushed stone and dimension stone. Within the dimension stone segment, companies mine, cut, and in some instances prepare stone blocks for such uses as building stone, monument stone, paving stone, and curbing. The dimension stone industry traditionally has accounted for only 0.5 to 1.0 percent of the 1 billion total tons of stone produced annually.
Dimension stone consists of both rough block and dressed stone. Rough stone accounted for 52 percent of all dimension stone produced by U.S. firms in 2003. Roughly 45 percent of rough block was used in building, and 23 percent was used in irregular shaped stone applications. The largest uses of dressed stone were flagging, curbing, and ashlar (a squared cut of stone used as facing material).
Among the many minerals mined for use as dimension stone by U.S. producers are basalt and diabase. Although these minerals, known collectively as trap rock or "trap," are primarily used in crushed stone, small amounts are quarried, cut, and polished as "black granite" for dimension stone. Because traprock dimension products are low-cost commodities in the stone market, they become less profitable as they are transported farther from mining locations. As a result, proximity to end-use markets or inexpensive modes of transportation are considered more important than their properties as minerals.
Another material commonly used as dimension stone is granite. The granite category includes "true" granite, granite gneiss, syenite and diorite, and some forms of granite-gabbro. Dimension granite is used in monuments and memorials; in heavy construction as large blocks; in residential and other buildings as foundation blocks, steps, and columns known as ashlar (when cut to regular shapes and sizes); and as paving stones and curbstones. Factors influencing the value of dimension granite deposits include color, uniformity of texture, and hardness. Besides final appearance, these factors also affect the cost of quarrying, cutting, and "dressing" or processing the rock.
The production of dimension granite historically has occurred in three regions: New England, the Southeast, and the midwestern states of Minnesota, Wisconsin, and South Dakota. Smaller amounts of dimension granite were produced in 14 other states.
Limestone is another material with numerous applications as dimension stone. Mines in Indiana traditionally have accounted for 60 percent of the dimension limestone produced in the United States. Dimension limestone is used nationally for the exteriors of commercial and institutional buildings as "Indiana" or "Bedford stone." Valuable properties of dimension limestone include uniformity of color and texture as well as the absence of elements such as stain-forming iron sulfide and quartz or chert, which impeded extraction of the stone.
Dolomite is a geologically recrystallized form of limestone used for dimension stone, and polished crystalline limestone is sold as "orthomarble." When first quarried, orthomarble is soft and easily worked and can be readily planed and carved into desired shapes. Orthomarble mines in eastern Tennessee produce a limestone known as "Tennessee marble" that ranges in color from light gray to pink, red, and brown, and is used in interior floors, panels, wainscoting, windowsills, and to a lesser extent in exterior construction.
Another popular material used as dimension stone is marble. The term marble applies commercially to any stone, other than granite, that had an attractive appearance and takes a polish. Most rock marketed as marble is not true marble but metamorphic marble, crystallized limestone, cave onyx, travertine, or verde antique (or serpentine). The most common element in true marbles is calcite, although the highest grades of statuary stone are more than 99 percent calcium carbonate. Pure marble is white, but common color variations include light gray, green, red, cream, and black.
Major uses for cut and polished marble are as architectural and statuary stone. More than 50 percent of marble production is utilized in constructing building exteriors as well as interior floors, steps, sills, wainscoting, columns, and trim. Most of the remainder became memorial or statuary stone. Important properties affecting the value of dimension marble include color, texture, hardness, porosity, solubility, and strength. Marble can be worked profitably only on a large scale, and new quarries cannot be economically opened or old ones extended without positive indications that a large bed of stone is present.
The states of Vermont and Georgia produce the bulk of building and monument marble, but other producing states include Alabama, Colorado, Maryland, and North Carolina. Vermont marble quarries are often as deep as 400 feet, and single blocks of Vermont marble weighing as much as 65 tons are used for such purposes as fountain base stones. Georgia marble is used in buildings, monuments, and memorials. Well-known marble structures include the Buckingham Fountain in Chicago and the face of the New York Stock Exchange.
Sandstone provides another material appropriate for use as dimension stone. Dimensions and stone is used for exterior facing and trim on large buildings, for "ashlar" in residential construction, as flagstones and curbstones, and in retaining walls and bridge abutments. Dimension sandstone ranges in texture from very fine to coarse and in deposit depth from a few inches to 200 feet. Some of the most desired colors in sandstones include shades of gray and tan. Uniformity of color in dimension stone is typically favored, but some producers market dimension stones that oxidized during weathering to produce aesthetically appealing spotted and streaked patterns.
Dimension slate is widely used for roofing purposes because it is easily prepared and fixed, weatherproof and durable, and often cheaper than and superior to other roofing materials. An average roofing tile of the highest grade of rock is only about five millimeters thick, which reduces strain on walls and roof supports. In addition to its use in roofing and flagstones, much dimension slate historically was produced as "mill stock" for switchboards and electrical panels, blackboards, mantels, baseboards, steps, sills, and grave vaults. Colored slate, which included red, purple, green, black, and gray, was favored for flagstone.
Techniques for quarrying dimension stone varied according to the type of rock, the depth of the deposit, and the end-use of the mined stone. Unlike some other minerals, which were processed into their marketable form at processing plants and simply extracted from the ground in the most economical fashion possible, the specific enduse of a dimension stone product determined the procedure used to quarry it. Ideal end-products—large, solid, relatively flawless blocks of stone of attractive texture and color—were carefully cut from quarries one by one.
The exact type of quarry excavated by industry firms depended on the nature of the terrain in which the deposit was located. A deposit extending into a hill, for example, could be entered from the side by digging a "bench" quarry. Such quarries provided long, high faces from which the granite could be blasted, as well as direct approaches to the quarry for removal of the mined rock. When granite deposits were located under flat ground, a pit quarry had to be excavated—either wide and shallow quarries for deposits of uniform quality extending overlarge areas, or deep quarries extending from 20 to 300 feet for narrow deposits of great depth.
Most dimension stone was cut from the quarry face into large blocks, undercut at quarry"floor" level, and pried free by wedging. The stone was then cut into "mill blocks" of the desired size (typically from 10 to 60 feet long, 4 feet wide, and 4 to 12 feet thick) by drilling and wedging, and then hoisted from the quarry by derricks. Although light blasting was sometimes used to loosen deposits, explosives were usually avoided because they could damage the rock.
Granite and sandstone quarrying usually involved "broaching," wire sawing, or jet piercing mining methods after the covering rock and silt were removed by scrapers or steam shovels. Broaching consisted of drilling a row of closely aligned holes in the rock face with tungsten carbide drill bits, then removing the blocks between the holes with broaching tools. Wire sawing involved the application of tensioned single-or triple-strand wire cables up to 16,000 feet long, which were drawn through pulleys. The cables formed a "saw" that was held against the rock and fed with a mixture of water and sand, cutting the stone by abrasion at a rate of about two inches per hour (in hard granite). When cutting was completed, channels of about a quarter of an inch wide and 50 to 70 feet deep remained from which the mill blocks could be extracted.
In sandstone and granite deposits with inherent strains or internal pressure, the drilled holes sometimes closed around the drill bit, rendering it ineffective. In such cases, a jet-piercing drill—in which a combustible mixture of oxygen and fuel from the drill's nozzle was used to blast the rock into fragments—could be employed to cut an eight-inch channel through the deposit face. Blocks could then be cut into the desired dimensions and lifted from the quarry by derricks into rail cars for transport to the dressing or preparation mill.
Another method traditionally used by dimension granite miners in shallow quarries involved drilling sixto eight-foot holes (depending on the desired size of the block) and placing small explosive charges into them to create a "parting" in the rock. Compressed air then was forced into pipes cemented in the holes, separating the desired sheet from the rock below. Using this method, granite miners could peel off segments of stone in desired sizes as they were needed.
In marble, limestone, and soft sandstone quarries, electrically powered channeling machines with steel chisels—which moved in a chopping motion back and forth on a track—could be used to cut through the stone. Such machines usually left channels about 2 inches wide, 10 to 12 feet deep, and 4 feet apart. After these initial cuts, drill holes were made into the rock and blocks were loosened from the quarry floor by wedges inserted in the holes. These loosened blocks could then be fashioned into smaller blocks using the "plug and feather" method. Feathers were elongated strips of iron, which were inserted in rows of drill holes. Plugs, or steel wedges, were driven between the "feathers" and alternately struck until a fracture appeared, forcing the feathers and loosening the stone.
Marble quarrying was typically affected by such factors as the "dip" or shape of the marble beds, the quality of the deposit, the expected price of the mined rock, the thickness of the overburden, and the uniformity of the marble. The chief goal of marble quarrying was to produce sound blocks of uniform quality, and quarrying procedures were tailored to each deposit. Marble beds of high value could be worked laterally or vertically through deep cuts made in the marble, while gently dipping layers of marble between solid walls of earth could be worked in deep open quarries.
In a typical marble mining operation, channel cuts were made six feet apart and eight feet deep across the quarry floor. The ends of the resulting strips were cut away from the walls, leaving blocks free to be drilled, wedged, and lifted out. Using this technique, the quarry floor was gradually lowered by successive eight-foot "benches."
Since most dimension stone was mined and dressed through contracts for specific jobs, preparation plants or mills operated by industry firms kept extensive drafting and pattern-making departments to anticipate required stone sizes. Drawings were prepared that detailed the exact dimensions of the requested stone, which were then referred to regularly during the stone finishing or dressing stage. Sawing, planing, rubbing, and polishing with stoneworking machines were among the processes employed in the finishing stage. Finished stones were then carefully marked and packed for shipment.
Between 1987 and 1992, employment in the U.S. dimension stone industry increased 8 percent to 1,400. Companies with five or fewer employees comprised more than one-third of the industry's total shipments in dollar terms, and the number of industry establishments employing twenty or more employees fell from 13 percent in 1987 to only 10 percent in 1992. In 1992, nearly 79 percent of the industry's work force was involved in production, development, and exploration activities at an average income of $19,455. Nonproduction workers averaged annual wages of $30,333.
Major dimension stone industry events in the mid-1990s included major new industry projects, expanding reliance on foreign sources, and new technologies. In 1995, after many delays, the Denver International Airport opened a massive construction project that featured 20,000 square feet of two-centimeter thick marble slabs from the Colorado quarry that had supplied marble for the Lincoln Memorial and the Tomb of the Unknown Soldier. In July 1995, the Korean War Veterans Memorial was also unveiled, in which 41 panels of granite formed a 164-foot-long reflective wall on which were etched photographic images of the conflict. Although exports of U.S. dimension stone (primarily to Italy) decreased slightly in 1995, imports (mostly of dimension granite) rose to $476 million, primarily from Italy, Spain, India, and Canada. Indian green marble found growing use for kitchen countertops, and low-priced Chinese marble emerged as a new product in the U.S. market.
Also in 1995, the National Mining Association (NMA) was formed from the union of the National Coal Association and the American Mining Congress. The group, which represented the entire mining industry, said its initiatives would include advocating for policy and legislation that will promote the health of the industry. Specifically, the group was concerned with, in the words of 1995 association president Richard Lawson, the perception of the "environmental lobby [that] argues that 'public' land must be forever held virtually as wilderness in the public interest." The NMA expressed concern that such environmental initiatives could make resources, including
lands which were home to mineral resources, available only to select "special interests."
New technologies in the late 1990s included "thermally stable" waterjet stone-cutting drill bits for increased penetration rates and extended bit life and computerized wire saws that could cut complex images on monument faces. The images etched on the surface of the Korean War Veterans Memorial, for example, were made by high-precision etching and contour-cutting laser technology made possible by advances in computerized design. A 1997 industry periodical described a new extraction method that used diamond wire sawing machinery (as opposed to traditional hydraulic and mechanized drilling, smooth blasting, and wheel loading). The new technique, manufactured by Blue Pearl, reportedly resulted in smoother surfaces and reduced waste. Such new ways of extracting granite were tested in the United States, as well as Japan, Finland, Italy, and South Africa.
Fueled by the growing demand for "natural stone" finishes, new quarry and processing technologies emerged that permitted the fabrication of very thin stone products. Computers also aided the marketing efforts of industry firms. The explosion of the World Wide Web as a marketing tool in the mid-1990s enabled some dimension stone producers to display their wares through digitized images of their stone products on their own Web pages.
As consumption of dimension stone increased in the United States, so did reliance on imports. By 2003, imports accounted for roughly 86 percent of dimension stone used in the United States. This figure had grown steadily since 1999, when imports accounted for 75 percent of domestic consumption. The value of dimension stone imports grew 23 percent in 2003, from $1.19 billion to $1.46 billion, while the value of exports declined by 6 percent, from $64 million to $60 million.
Consumption of U.S. dimension stone has grown steadily since 1999, when it was valued at $1.01 billion. By 2003, consumption was valued at $1.63 billion. To offset competition from substitute materials such as steel, aluminum, reinforced concrete, lightweight and low-cost facing materials, plastics, glass, aluminum, and porcelain-enameled steel, industry firms had looked to the development of niche markets in granite and marble dimension stone for kitchens and bathrooms; limestone for landscaping, ledges, and tiles; and worked or hand-carved stone for custom-built houses. According to 2004 estimates by the U.S. Geological Survey, demand for dimension stone is expect to grow through 2014 due to the rising prices of substitute materials, as well as expanded varieties of stone and advances in dimension stone processing technology.
Cold Spring Granite Company, Rock of Ages Corporation, Fletcher Granite, Indiana Limestone, Georgia Marble, and Halquist Stone were among the industry's leading companies in the early 2000s. In 2003, Rock of Ages, which maintained nearly 40 granite quarries, billed itself as the "world's leading supplier of granite products" for memorials, mausoleums, and estate pieces. Primarily a supplier of granite blocks to other manufacturers, Rock of Ages was capable of producing 63,000 cubic meters of granite every year from its quarries. By the end of 2003, Rock of Ages had 100 retail outlets in 14 states and sold wholesale products through 160 independent retailers in the United States and Canada. Company sales during 2002 were $92.5 million, falling roughly 2 percent from the previous year, and employees totaled 860.
Georgia Marble was founded in 1835 by an Irish immigrant stone cutter. By 1997, the company was a subsidiary of IMETAL and the largest producer of marble products in the world, with more than 300 marble products produced by its industrial, consumer, and dimension stone divisions. Its dimension stone operations produced structural (panels, columns, and floor tiles) and memorial dimension stone, and its marble stones have been used in the memorials of such prominent Americans as Warren Harding, Thomas Jefferson, and Martin Luther King Jr. In the late 1990s the company had a sales range of $50 to $100 million. In 2003, Georgia Marble continued to operate as a subsidiary of IMERYS, the result of a merger between IMETAL and English China Clays.
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U.S. Geological Survey. Mineral Commodity Summaries, January 2004. Available from http://minerals.usgs.gov/minerals/pubs/mcs/2004/mcs2004.pdf .