Marble (rock)
Marble is a metamorphic rock that forms from the recrystallization of limestone or dolomite under heat and pressure. This geological process alters the rock, resulting in a coarser-grained, harder material primarily composed of calcite. Marble is commonly found in regions undergoing tectonic activity, such as the Italian Apennines and parts of the United States like Vermont, Georgia, and Alabama. Historically, marble has been valued for its aesthetic appeal and durability, making it a popular choice for architecture, sculpture, and monuments for over five thousand years. Renowned artists, including Michelangelo, have favored marble for its sculptural qualities. Quarrying marble involves large operations that have evolved from traditional methods to modern techniques, improving efficiency while maintaining the integrity of the material. Marble's chemical stability means it has minimal environmental impact during extraction, and its versatility extends to applications in flooring, wall coverings, and even electrical insulators. Overall, marble remains a significant and enduring material in both artistic and structural contexts.
Marble (rock)
Where Found
Marbles, geologically defined as metamorphically altered calcareous rocks, are found in the core areas of younger mountain chains formed by the collision of tectonic plates and the consequent uplift and distortion of carbonate sedimentary strata. They are also found in the exposed roots of ancient, very eroded mountain chains of continental shield areas. Important marble-producing areas include the Carrara area in the Italian Apennines and Vermont, Georgia, and Alabama in the United States.
Primary Uses
Marble is used in architecture as both an ornamental and a structural stone. It is also used as an artistic medium for three-dimensional art such as sculpture, interior furnishings, and mortuary and historical monuments.
Technical Definition
Geologists define marble as a type of rock produced by metamorphic processes acting on either limestone or dolomite (dolostone), causing recrystallization through heat and pressure to produce a coarser-grained, harder rock. Stonemasons and quarriers have a more generic definition, which calls almost any hard rock that accepts a fine polish marble.
Description, Distribution, and Forms
As defined geologically, marble is a type of rock composed primarily of calcite. It can be, like limestone, monomineralic in nature—that is, a rock composed of only one, or nearly one, mineral. Thus it can be up to 99 percent calcite (calcium carbonate). True marble can be derived from either limestone or dolomite (sometimes called dolostone). Dolomite (calcium magnesium carbonate) is a carbonate rock in which much, if not most, of the original calcium carbonate has been replaced by magnesium. True marbles are formed by two types of metamorphism: regional and contact. Regional metamorphism is usually tectonic in nature and involves the slow compression and heating of rocks by large-scale crustal movements of the Earth over long periods of time. Contact metamorphism is caused by rocks coming into contact, or near contact, with sources of great geologic heat, such as intruding bodies of magma; in these cases change can be effected within a short period of time.
History
Marble in its various forms has been known and admired since remote antiquity as a stone of choice for many applications. Some of the earliest known works of true architecture that have survived from ancient Mesopotamia, Egypt, and Greece featured marble as either decorative or structural elements. Sculptures, bas-reliefs, dedicatory columns, and triumphal arches have frequently featured various marbles. Thus marble has been in use at least five thousand years, dating back to the first civilizations, and its use continues up to the present. Many sculptors through the ages—among them such giants as Michelangelo, working in the fifteenth and sixteenth centuries in Italy—have preferred marble, especially the pure white varieties.
Obtaining Marble
Marbledeposits are quarried in large operations that may involve hundreds of workers. In Europe marble is often obtained from quarries that have been worked continuously since antiquity. Until the last century or so, work was laboriously performed with age-old traditional tools and methods, but with the advent of power equipment the methodology and speed of extraction have greatly improved. Some constants have remained, such as the general strategy regarding extraction of large blocks of marble: removing the overburden (overlying sediments and rubble, if any), defining a quarry floor and front by quarrying monolithic blocks of marble parallel to their natural jointing planes, cutting away large blocks on all sides and removing the marble to the quarry floor, trimming, removing the marble from the quarry, and transporting it to the purchaser (often by use of specially built railroad systems).
Marble extraction has never had significant environmental effects, as the true marbles are chemically inert for all practical purposes. The metamorphism they underwent in their natural development stabilized their constituent minerals, including the trace minerals such as iron and magnesium from which colored marbles derive their patterns and hues.
Uses of Marble
The primary importance of marble is its use in architectural columns, floorings, wall coverings, sculpture, vases and other receptacles, and monuments of all sorts. Beginning in the twentieth century, new minor uses were found for marble, including electrical outlet baseplates and other electrical insulators, as it is a good natural insulator.
Bibliography
Dietrich, R. V., and Brian J. Skinner. Gems, Granites, and Gravels: Knowing and Using Rocks and Minerals. New York: Cambridge University Press, 1990.
Kogel, Jessica Elzea, et al., eds. “Decorative Stone” and “Dimension Stone.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: Society for Mining, Metallurgy, and Exploration, 2006.
Mannoni, Luciana, and Tiziano Mannoni. Marble: The History of a Culture. New York: Facts On File, 1985.
Pellant, Chris. Rocks and Minerals. 2d American ed. New York: Dorling Kindersley, 2002.
Price, Monica T. The Sourcebook of Decorative Stone: An Illustrated Identification Guide. Buffalo, N.Y.: Firefly Books, 2007.
Robinson, George W. Minerals: An Illustrated Exploration of the Dynamic World of Minerals and Their Properties. Photography by Jeffrey A. Scovil. New York: Simon & Schuster, 1994.
Schumann, Walter. Handbook of Rocks, Minerals, and Gemstones. Translated by R. Bradshaw and K. A. G. Mills. Boston: Houghton Mifflin, 1993.
U.S. Geological Survey.
U.S. Geological Survey.