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Geological Sources of Building Stone NORMAN HERS Throughout history, the geologic availability of materials has been a principal factor affecting techniques of construction, structure and stability, decorative detail, and overall aesthetic aspects of buildings and monuments. Greece and Rome, for instance, had abundant, locally available stones, including marble and limestone, all of which were used in the construction of the principal monuments of classical times. In the United States, weathering-resistant, strong, and attractive building stones are abundant in all but one geological province: the Atlantic and Gulf Coastal Plain. Abundant stone is supplied by the other geological provinces, which are composed of crystalline rocks or older sedi- ments. Four states accounted for 51 percent of the total U.S. production of dimension stone in 1980: Indiana, a leader in limestone, and Georgia, Vermont, and New Hampshire in marble and granite. Granite accounted for 50 percent of domestic production; the rest, in order of volume, were limestone, sand- stone, slate, and marble. Throughout recorded history man has had a special relationship with building stone. He was quite content to construct his own home out of timber, mud wattle, thatch, or whatever other matenals were easily worked and available; but for his monumental buildings, only the most beautiful and durable stone would do. We think of ancient Athens as a city of gleaming marble, of the monumental buildings of the Acrop- Norman Herz is Professor of Geology, Department of Geology, University of Georgia, Athens. 49

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50 CONSERVATION OF HISTORIC STONE BUILDINGS olis and of the Agora, when in all probability its principal aspect must have been that of unbaked, sun-dried brick the adobe of our south- western United Statescapped by terra-cotta roof tiles. WycherIey has speculated that the view from the Acropolis today, of red-tile roofs, must be identical to that of classical times.) What has lasted over two millenia are not the adobe dwellings but the buildings and monuments constructed of gleaming white marble from Mount Pentelikon in At- tika or from the island of Paros in the CycIades. The ancient Greeks sought to preserve and transmit to later generations what they deemed most significant in their culture not their mean day-to-day existence but their philosophy, religion, and form of government; and this could best be done through marble monuments. Almost all important cultures in both the Ad World and the New World have shared this special feeling about building stone. Primitive societies set up stone calms to memorialize the site of important events or to mark important routes. More advanced cultures quarried and used dimension stones to construct monuments and buildings, again with the thought of preserving what they thought most important in their heritage. In this century we have moved steadily from buildings constructed principally of dimension stone to those using materials that are easier and cheaper to handle, such as steel and concrete. How- ever, when we deem a building monumental in scope, such as the new National Gallery of Art, marble is still used. In many architectural designs, dimension stone is used as a thin curtain wall or veneer, in slabs 7/8 in. to 5 in. thick, to add grace and beauty to what may appear otherwise aesthetically less attractive constructions. The term "stone" as used in this country includes all consolidated rock that is mined or quarried and used for construction, roads, or chemical, metallurgical, and agricultural activities. As a construction material, dimension stone is prepared to predetermined size and finish. About 314 B.C., Theophrastus listed characteristics that made building stone valuable: (al found in large areas and made up of whole layers; (b) can be extracted in whole blocks; {c) possesses a pleasing color and other aesthetic features, such as (~) smoothness; and (e) is relatively hard, i.e., structurally strong.2 In the 2300 years since these observa- tions, all we have added is the ability to resist the accelerated weath- ering common in today's urban or acid-rain environment. The availability of building stones was an important architectural consideration until the start of this century. Abundant limestone and marble in classical Greece enabled the architect to develop a unique style that combined elaborate use of marble with delicate decorative detail in all visible parts of the buildings. Limestone and marl blocks

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Geological Sources of Building Stone 51 were used to lighten the building superstructure, but they were always veneered with marble. The Romans, on the other hand, developed massive structures that generally employed less marble and more con- crete, although all building materials of the known world were avail- able to and used by Roman architects. Rome developed many concepts and systems, such as mass production, accumulation of stocks, pre- fabrication, and standardization of qualities and dimensions of building stones and other materials. This made it possible to accomplish such feats as building the Pantheon in less than 10 years Pa. 118-128 A.D.) and the Baths of Diocletian in less than 8 (ca. 298 - 306 A.D.~.3 The flowering of the Gothic cathedral was related directly to the availability of attractive and easily quarried sedimentary rocks. In the Middle Ages the cost of quarrying and finishing the stone equalled the cost of transportin.g it 12 miles from the Quarry site. so that local stone _ ~ . , , ~ _ ]] 1 , . 1 . 1 ~ . ~ ~ A ~ . _ generally dictated the architectural style,4 but important exceptions always existed for the most prestigious buildings. Much of the stone- work for the Norman cathedral at Canterbury, for example, was ob- tained from quarries in Caen, France. As our own capital has grown in prestige and international importance, we have also used a greater variety of exotic building stones, such as Carrara marble and travertine from Italy, larvikite from Norway, and anorthosite from Canada. VARIETIES OF BUILDING STONES Almost every kind of rock can be used as dimension stone.5 The prin- cipal controls on usage are aesthetic appeal and physical properties, including resistance to weathering. The geological definition of a rock is based on its chemistry, fabric, and mineralogy; these attributes are also the principal determinants of its properties. The American Society for Testing and Materials (ASTM) has adopted standard definitions for the principal commercial dimension stones. Building stones are de- scribed below both from the geological once ASTM points of view. Rocks are divided into three overlapping genetic groups: Sedimentary rocks, such as limestone and sandstone. Igneous rocks, such as granite and diabase (traprock). Metamorphic rocks, such as marble and slate. Limestone ASTM defines limestone as a rock of sedimentary origin, composed principally of calcium carbonate (calcite) or the double carbonate of

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52 CONSERVATION OF HISTORIC STONE BUILDINGS calcium and magnesium (dolomite!. The textures vary greatly, from uniform grain size and color to a cemented-shell mash. Oolitic lime- stone, a popular building stone in this country, Britain, and France, consists of cemented rounded grains of calcite or aragonite generally under 2 mrn in diameter. Some limestones have varying amounts of other material, such as quartz sand or clay mixed in with the carbonate minerals. Most limestones are formed of shells or reworked shell frag- ments, although many commercial limestones, including colitic and very fine-grained and compact varieties, are chemical precipitates. Sandstone ASTM defines sandstone as "a consolidated sand in which the grains are composed chiefly of quartz and feldspar, of fragmental texture, and with various interstitial cementing materials, including silica, iron oxides, calcite, or clay." Commercially used sandstone is a cIastic sediment consisting almost entirely of quartz grains, 1/16 to 2 mrn in diameter, with various types of cementing material. Enough voids generally remain in the rock to give it considerable permeability and porosity. In the United States, commercially available sandstones in- clude the well-known brownstone, an arkosic sandstone that is rich in feldspar grains and was quarried in the Triassic basins of the eastern states. Travertine Travertine is a variety of limestone deposited from solution in ground- waters and surface waters. When it occurs hard and compact and in extensive beds, as around Rome, it can be quarried and used as an attractive building stone. It is generally variegated gray and white or buff, with irregularly shaped pores distributed throughout the ground- mass. Granite Commercial granite includes almost all rocks of igneous origin. True granites consist of alkali feldspars and quartz with varying amounts of other minerals, such as micas and homblende, in an interlocking and granular texture, and with all mineral constituents visible to the naked eye. Geologically, granite is distinguished from other rocks that it resembles, such as granodiorite, quartz monozonite, and syenite, on the basis of the percentages of quartz, potassium feldspar, and plagio-

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Geological Sources of Building Stone 53 cIase feldspar. This distinction is not made commercially; in fact, black fine-grained igneous rocks, such as basalt or diabase, are commonly called "black granite." Other dark "granites" include rocks that, pet- rographically, are anorthosite, gabbro, syenite, and charnockite. Marble According to ASTM, commercial marble includes all crystalline rocks composed predominantly of calcite, dolomite, or serpentine and ca- pable of taking a high polish. Geologically, marble is considered only as a metamorphic rock foxed by the recrystallization of a limestone or dolomite under relatively high heat and pressure. Thus, in addition to geological marble, commercial marble includes many crystalline limestones, travertine, and serpentine, a metamorphosed ultramafic rock. In the metamorphic process, original sedimentary features, ex- cept for bedding, which is preserved as a compositional layering, are destroyed. The original minerals, calcite and dolomite, are recrystal- lized in an interlocking mosaic texture, and the impurities form mag- nesium and iron silicates. The color of many marbles is due to these accessory minerals, such as talc, chlorite, amphiboles, and pyroxenes, as well as iron oxides, hydroxides, sulfides, and graphite. Slate ASTM requires a slate to possess an excellent parallel cleavage that allows the rock to be split with relative ease into thin slabs. Slate is a metamorphosed rock derived from argillaceous sediments consisting of extremely fine-grained quartz, the dominant mineral, and mica and other platy minerals. The color of state is generally determined by the oxidation state of the iron or the presence of graphite or pyrite. Other Types A great variety of other types of rocks are sold commercially, including: {a) quartzite a metamorphosed sandstone consisting almost entirely of quartz and utilized locally, as the Sioux Falls quartzite of South Dakota and the Baraboo quartzite of Wisconsin; (b) greenstone~e- fined by ASTM as a metamorphic rock principally containing chlorite, epidote, or actinolite; (c) basalt or traprock- a microcrystalline vol- canic or dike rock that consists primarily of pyroxene and a calcic plagiocIase (the stark black churches of the Auvergne of Central France are largely made of basalt); and (I) obsidian a volcanic glass that

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54 CONSERVATION OF HISTORIC STONE BUILDINGS commercially includes pumice in the United States, has low density because of its frothy texture, and Con be easily shaped with hand tools. BUILDING STONE IN THE UNITED STATES In the early part of this century the total value of dimension stone produced was greater then that of crushed stone.6 As other materials were substituted for dimension stone in construction, and as a national highway program was developed, these roles were reversed. In recent years the total amount of dimension stone has been less than 0.5 percent of total stone produced and its value about 4 percent of the total. Despite this decline in relative production, the actual amount of dimension stone produced since 1973 has not varied greatly from 1.5 million tons. A high of 1.9 million tons was reached in 1974 and a low of 1.3 million tons in 1980. The total value of `dimension stone increased from $86.0 million in 1973 to $147 million in 1981. ISee Table 1.16 7 The total production of dimension stone in 1981 increased less than 1 percent over 1980 but its value rose 6 percent. In 1981 in terms of volume, about 50 percent of the production was granite, 22 percent limestone, 13 percent sandstone, 5 percent marble, and 7 percent slate. In 1979 marble was the most costly at $177 per ton, followed by slate, $147; granite, $110; limestone, $55; and sandstone, $40. In 1980, di- mension stone was produced in 39 states by 263 companies operating 426 quarries. Leading states were Georgia, which produced 18. 1 percent of U.S. building stone; Indiana, 13.4 percent; Vermont, 13.4 percent; and New Hampshire, 6.3 percent. These four states accounted for just TABLE 1 U.S. Production of Dimension Stone, 1929-1981 Value Tons Produced (millions of Year {millions) dollars) 1929 4.7 70 1939 2.3 25 1949 1.8 52 1959 2.3 25 1969 1.9 99 1979 1.35 123 1981 1.32 147 SOURCE: U.S. Bureau of Mines, 1975, 1982.

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Geological Sources of Building Stone 55 over half of domestic production. Other states producing more than 35,000 tons in 1980 include California, Massachusetts, Minnesota, North Carolina, Ohio, Pennsylvania, South Dakota, Texas, and Wis- consin. Domestic reserves of building stone must be considered inexhaust- ible,5 although shortages of special varieties may develop because of economic or aesthetic factors. Geological controls of various types of rocks are such- that all common builcting-stones occur abundantly in nature, so that the exhaustion of;one quarry or district can quickly lead to the discovery and exploitation of similar stone in another dis- trict. The factors that determine whether a new building stone district should be opened are economic and environmental: Can the stone be quarried, finished, and transported to markets under existing environ- mental regulations and at competitive prices? The most important markets have been the more densely populated areasthe Northeast, upper Midwest, and Southern California- but this picture is changing as people move to the Southwest, or Sun Belt. The list of the principal producing states shows that the dimension stone industry has been concentrated in areas where the geology is favorable, but also where traditional markets are not too far removed. The distributional and geological controls over building stone pro- duction in the United States are best understood from the point of view of lithologic provinces [Figure 11. Five provinces can be distin- guishe`1, corresponding roughly to physiographic provinces, that con- trol the lithologic types found in each.5 These are {a) Atlantic and Gulf Coastal Plain, (b) Appalachian Crystalline Province, C) Central-Interior Sedimentary Basins, {~) Lake Superior Crystalline Province, and (e) Western Province. The Appalachian and the Central-Interior provinces have produced the greatest amounts of building stones, being blessed with both favorable geology and proximity to markets. AtIantic and Gulf Coastal Plain The Atlantic and Gulf Coastal Plain Province commences in the south- eastern half of New Jersey and includes part or ah of the coastal states to Texas. It is generally underlain by poorly consolidated sedimentary rocks of Cretaceous to Recent age that lie in nearly honzontal layers. Very little dimension stone has been produced because the rocks lack strength, although in Colonial times a coquina limestone that harfd- ened when exposed to the air was widely used in Flonda and other southeastern states.

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56 CONSERVATION OF HISTORIC STONE BUILDINGS 1. Atlantic & Gulf Coastal Plain 2. Appalachian Crystallines T = Triassic basins 3. Central-lnterior Basins G = granite 4. Lake Superior Crystallines 5. Western Province , , ~ r r A '~1 ~~> bird i 'I 1~ ') ^~ ~ ~ ~ _,,'~._.- - ~~ fit 0 400 \ ~ ,0 . , 400 FIGURE 1 Lithologic provinces of the United States. SOURCE: Laurence, 1973.8 Appalachian Crystalline Province The Appalachian Crystalline Province includes the Appalachian mountain belt, from the Blue Ridge and Piedmont in the south, north- ward to the Reading Prong and New Tersey-Hudson Highlands, the Adirondack Mountains, and New England. Included geographically within this province is the lithologically unrelated Triassic Basin Sub- province. This province consists of crystalline rocks, both igneous and met- amorphic, of Precambrian and Paleozoic age that formed under rela- tively high pressures fi.e., deep burial) and high temperatures. Uplift and erosion have exposed this ancient "root zone" of what must have been at one time much higher mountain ranges. This province leads in the production of granite, slate, marble, serpentine, and other crys- talline rocks and has the added attribute of proximity to important markets. Slate is principally produced in Virginia, Pennsylvania, New York, and Vermont; marble in Georgia, Vermont, and Alabama; and serpentine and verde antique in Vermont and Virginia. Granite has been produced in almost every state within the province, principally in Georgia but also in Connecticut, Rhode Island, Massachusetts, New

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Geological Sources of Building Stone Hampshire, Vermont, New York, Pennsylvania, North Carolina, and South Carolina. The Triassic Basin Subprovince was formed before the continental breakup of North America and Europe-Africa. It consists of down- faulted basins with tilted but undeformed sedimentary rocks, as well as basaltic flows and diabasic dike rocks (traprock). The three principal basins are (a) along the Connecticut River, where a large production of brownstone, an arkosic red sandstone, was used in building con- struction in many large eastern cities around the turn of the century (production now is negligible because the stone does not resist the accelerated weathering of modem city environments); (b) the Newark Basin of New Jersey, which has produced much traprock; and (c) the Triassic Basins of Virginia. 57 Central-Interior Sedimentary Basins The Central-Interior Sedimentary Basins are generally underlain by flat-lying sedimentary rocks of Paleozoic, Mesozoic, and Cenozoic age and also include a few very important areas of crystalline rocks. The province extends from the western slopes of the Appalachian Moun- tains to the foothills of the Rocky Mountains. The only areas where the rocks are not flat-lying, but are rather complexly folded and faulted, are in the Valley and Ridge Physiographic Province, just west of the Blue Ridge, and the Ouachita Mountains of Oklahoma and Arkansas. Crystalline rocks are exposed in the cores of domal uplifts, as in the Black Hills of South Dakota and elsewhere. The eastern two-thirds of the province is underlain by Paleozoic sedimentary rocks that have produced more than 80 percent of the total domestic sandstone and limestone. Good geological controls are evident in the distribution of the quarried stones. The province was a vast inland sea during most of the Paleozoic and bordered on the ancient Appalachia landmass. Nearshore, detrital sandstones were laid down; to the west, in the shallow seas away from the ancient shoreline, carbonate limestones were precipitated. Thus sandstone is produced in New York, Ohio, and Pennsylvania, closer to the ancient shoreline, and the largest limestone production is farther west, in Indiana and Missouri. Granite exposed in this province is an important source of building stone and is produced in South Dakota, Missouri, Oklahoma, and Texas.

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58 CONSERVATION OF HISTORIC STONE BUILDINGS Lake Superior Crystalline Province The Lake Superior Crystalline Province comprises parts of Minnesota, Wisconsin, and Michigan at the southward terminus of the much greater Canadian Shield Province of Precambrian age. This small U.S. province has produced much granite; in fact, it stands second after the Appalachian Crystallines in production. Western Province The Westem Province includes the area from the Rocky Mountain foothills to the Pacific Ocean. Geologically, there are a great number of lithologic subprovinces represented that formed in many different environments. A great variety of rocks can be found; the sole limitation on dimension-stone production from this area is the distance to viable market centers. All the principal types of building stones are produced in this area. Granite is the most widespread and has been quarried in California, Colorado, and Washington. Sandstone has come principally from the Colorado Plateau and limestone from California. Travertine has been quarried in Idaho and obsidian and pumice in California and Nevada. Much of the production has been near the large population centers of southern California. FOREIGN SO URCES Tariffs on dimension stone vary from zero to 12.7 percent ad valorem for most-favored nations, according to type, size, value, and degree of preparation. In the period 1978-80 in terms of value, Italy supplied 71 percent of imports of dimension stone, Canada 9 percent, Mexico 5 percent, and all other countries 15 percent. In tees of total value, we export less then half of what we import: In 1980, exports were $36.4 nonillion and imports $88.9 million. Italy dominates the international trade in dimension stone; it is the leading importer of rough blocks and the leading exporter of finished stone. The principal export has been marble, especially from the Carrara district; but travertine from around Tivoli, serpentine, volcanic tuff, and limestone are also ex- ported. Other countries have supplied many types of granite, true gran- ite as well-as the so-called black granite of Canada (anorthosite from Lac Saint lean) and of Norway (larvikite).

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Geological Sources of Building Stone TECHNOLOGY 59 The dimension stone industry is labor intensive, has been so in the past, and must remain so in the foreseeable future. This has hampered growth and more widespread use of building stone, since production methods remain slow, cumbersome, ant! costly.9 Research on extrac- tive and finishing equipment has recently resulted in improvement of basic designs and has helped keep the cost of building stone lower than expected in terms of normal inflation. Modernization has in- volved the use of high-speed, diamond stone saws, grinders, and drills, as well as improved conventional wire saws and jet or water-piercing drills. Little blasting can be done in mining dimension stone, and quarrying must involve the use of diamond saws, wire saws, and drill- ing machines. Large circular saws~are used for final processing; some are 1Q it (3 m) or more in diameter with diamond or steel shot inserts. Similar equipment, utilizing diamond saws and abrasives, is employed for the final polishing and decorating of the stone. ENVIRONMENTAL PROBLEMS Environmental problems confront stone producers to a greater extent than they do producers of almost any other mineral cornmodity.6 The problems arise not from noxious waste products but because many quarries are in urban areas, close to their potential markets. Such problems include high noise levels from quarrying operations, dust from mining and sawing, solid waste blocks left on the surface, and general unsightliness. Rarely, as happened in a serpentine quarry in Maryland, particulate asbestos derived from asbestos fibers in the rock is detected in air. The question of possible health hazards from such sources has been studied by both the EPA and the Bureau of Mines, which has established a Particulate Mineralogy Unit to examine fur- ther and classify rock-derived dusts and fibers. None of these environ- mental problems is insoluble, except possibly those relating to ser- pentine, which is one of the least important of the building stones. The single major threat to stone resources is probably competing land uses. Once the deposits have been covered by building lots or made into parks or recreational areas, they are removed as potential sources of raw materials. Large eastern cities such as New York, which must now obtain much of its sand and gravel for construction from the floor of the continental shelf, are prime examples of the conse- quences of unlimited development without planning for future raw material sources. Land rehabilitation after depletion of dimensional

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60 CONSERVATION OF HISTORIC STONE BUILDINGS stone deposits by surface mining can also be very costly. In the average mining operation, ore is extracted, and the waste, generally most of the mined rock, can be resumed to the hole left by quarrying to help recontour the surface. In a dimension stone quarry much of the stone removed is used, and restoration of the land to its previous surface using on-site wastes is all but impossible. OUTLOOK The demand for dimension stone has been relatively stable or decreas- ing slightly since 1962. The only way that the competitive position of stone relative to other construction materials could be improved would be to develop low-cost methods of extraction and maintain consistent standards of color and strength in large-scare, rapid con- struction projects. In many parts of Georgia, for instance, granite is a much stronger and cheaper curbstone material than concrete because of improved production methods. Stone may develop discoloration or weathering soon after being put in place in a monument or construction.~ Methods for more rapid testing of dimension stones are needed. Such tests must also include exposure of the stone to various types of environments. Conservation of building stone, in the sense of conservation of a natural resource, is not a problem. Our domestic resources are inex- haustible, although real or potential shortages in localized areas can be serious. Once an area has been identified as the source of a strong and attractive building stone, every effort should be made to preserve it by zoning laws and by conscious efforts to discourage urban devel- opment within it. Geological studies by the federal and state govern- ments should always identify potential sources of building stones. Perhaps a data base can be built up of future sources, especially deposits that merit special legal protection so that they can be preserved until needed. So Tong as man believes in preserving his cultural heritage and trans- mitting his monuments to future generations, his primary concerns must remain the preservation, production, and protection of durable and attractive building stones. REFERENCES b 1. R.E. Wycherley, The Stones of Athens (Princeton, NJ., 1978~. 2. A. Dworakowska, Quames in Ancient Greece, Polish Academy of Sciences, Bib- liotheca Antiqua, 14 (1975~. 3. J.B. Ward-Perkins, Roman Architecture tH.N. Abrams: New York, 1977~.

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Geological Sources of Building Stone 4. P. McCleary, Structure and Intuition, American Institute Architect journal, 69~12), pp. 5~59, 119 {1980~. 5. W.R. Power, Dimension and Cut Stone, pp. 157-174 in Industrial Minerals and Rocks, S.J. Lefond, ed. {American Institute of Mining Engineers: New York, 1975~. 6. J.E. Shelton and H.J. Drake, Stone, pp. 1031-1048 in Mineral Facts and Problems, 1975 {U.S. Bureau of Mines: Washington, D.C., 1976. 7. U.S. Bureau of Mines, Stone in 1981, Mineral Industry Surveys (U.S. Bureau of Mines: Washington, D.C., 1982~. 8. R.A. Laurence, Construction Stone, in U.S. Geological Survey Professional Paper 820, pp. 157-162 ~ 1973~. 9. A.H. Reed, Stone: Mineral Commodity Profile 17 {U.S. Bureau of Mines: Wash- ington, D.C., 1978i. 10. E.M. Winkler, Stone: Properties, Durability in Man's Environment, 2nd edition {Springer-Verlag: Newt York, 1975~. 61