Vermont State Stone
Granite is a hard, crystalline, plutonic igneous or (possibly) metamorphic rock. Its medium-to-large crystal size gives it a flecked or granular appearance, thus its name, from the Latingranum. Granite varies in composition depending on the parent rock that melts or partially melts to form it; the dominant components are silica and feldspar, which form the lighter-colored parts of the rock. The darker parts may be biotite, hornblende, muscovite, pyroxene, or other minerals. Granite is most often predominantly white, gray, pink, or red. Green and brown granites also occur. So-called "black granites" are really mafic (magnesium/ferric) rocks, not granite, which is felsic (feldspar/siliceous).
A STATE SYMBOL
In 1992, Vermont named three official state rocks: granite, marble, and slate. Vermont has been quarrying granite for over two centuries and has supplied building material to many U.S. cities. Barre, the center of the quarrying activity, is home to Rock of Ages, the world’s largest granite quarry, which is more than 125 years old.
Barre was already quarrying granite in a small way in 1875, when the railway opened in the little town. A great burst of growth followed, generated by 68 granite quarries shipping fine granite far and wide. The industry attracted quarry workers from England and Sweden and carving artisans from Italy and Scotland, shaping the cultural makeup of the area. Another quarrying locale, Woodbury, sold several varieties of granite including Woodbury gray, Bethel (or peerless white), imperial blue, and Vermont white.
A museum dedicated to the granite industry is under development in Barre. The museum will feature exhibits on the geology, technology, history, and culture of the granite quarries so vital to the city and the state. The site also includes a stone arts school.
Granite is plutonic, which means it forms underground, and is at least sometimes igneous, meaning it forms from magma. The underground origin allows slow cooling of the magma or parent rock and accounts for the medium to large crystal size characteristic of the rock.
Geologists have searched for a means to explain how so much granite rises from the earth’s lower crust where it originates into the upper crust. Tectonic uplift and surface erosion may lead to granite’s exposure at the surface; however, these forces are not sufficient to account for the emplacement of most granite. Major theories presume that granite moves upward through surface rocks while it is still relatively hot, either pushing the other rocks aside or filling gaps at fault lines.
Another disputed question is whether the majority of granite is actually metamorphic (silicified from softer rock). The prevailing theory remains that granite is primarily igneous.
Granite is the principal bedrock underlying large parts of northeastern Vermont; it also occurs as intrusions in rocks throughout the eastern half of the state and along the Lake Champlain shoreline. Worldwide, granite is widespread in continental landforms. It is the primary material of numerous mountain ranges formed above tectonic subduction zones; low-relief granite plutons, such as the vast Laurentian Shield of North America, underlie flatter topography as well. By contrast, the ocean floor is primarily made of basalt.
Granite is one of the most favored stones for building construction because of its load-bearing capacity and resistance to weathering. In rough form, it is also a material of choice for other applications where toughness is essential, such as for breakwaters and riprap (shoreline protection), and for interiors where its hardness and glossy finish are both practical and beautiful. Granite aggregate is used for railroad ballast and as chip seal for road surfaces.
Two quarries in Vermont still produce dimension stone (stone cut for architectural use). A recent project of the Woodbury Quarries has been an addition to the Pennsylvania state capitol (see Famous Examples section below). Granite quarries also produce crushed stone; in 2006, 278,000 tons of crushed stone quarried in Vermont were sold for a total of $2.8 million.
Vermont’s Woodbury gray granite built Chicago’s Cook County Courthouse and City Hall in 1885, and the Carnegie Library in Syracuse, New York in 1907. The most famous building using Vermont granite is the Pennsylvania State Capitol, completed in 1906 and faced with Woodbury gray granite.
Granite is used throughout the world in buildings and monuments. Aberdeen, Scotland, and Hyderabad, India, are two cities that have used great quantities of locally quarried granite in their buildings; Aberdeen is nicknamed "the Granite City."
Because granite endures weathering better than most rocks, it forms some of the nation’s most impressive stone outcrops. The granite formations of Yosemite National Park are among the most famous.
Chemical Formula: SiO2
Color: White, gray, pink or red
Chemical Formula: CaCO3
Color: White or lightly colored, usually with dark streaks
Chemical Formula: Varies, primarily SiO2 & KAl2(Si3Al)O10(OH,F)2
|Author: World Trade Press|