granite, coarse-grained igneous rock of even texture and light color, composed chiefly of quartz and feldspars. It usually contains small quantities of mica or hornblende, and minor accessory minerals may be present. Depending on the feldspar present, granite may be pink, dark gray, or light gray. It is commonly believed to have solidified from molten rock (called magma) under pressure. However, some granites show no contacts with surrounding wall rock, but instead gradually grade into metamorphic rock. Others show relic features found in sediments. This evidence suggests that some granites are not igneous in origin, but metamorphic. Some granites are the oldest known rocks on earth; others were formed during younger geologic periods. Crystallized at depth, granite masses are exposed at the earth's surface by crustal movement or by the erosion of overlying rocks. Very coarse-grained granite, called pegmatite, may contain minerals and gemstones of economic value. Such pegmatites are found in the Black Hills of South Dakota. Granite has been used since ancient times as a building material.

Granite City, city (1990 pop. 32,862), Madison co., SW Ill., an industrial suburb of East St. Louis, on the Mississippi; inc. 1896. It has port and rail connections. Some metal products are manufactured; however, the suburb has been affected by the surrounding cities and area, which have become highly depressed economically due to declining industries.

Coarse- or medium-grained intrusive rock that is rich in quartz and alkali feldspar. One of the most common rocks of the Earth's crust, it is formed by the cooling of magma. Granite was once used extensively as paving blocks and building stone, but today its principal uses are as roadway curbing, veneer for building faces, and tombstones. Granite characteristically forms irregular masses of extremely variable size, ranging from less than 5 mi (8 km) in maximum dimension to larger masses (batholiths) that are often hundreds of square miles in area.

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