Granite

Granite is a common and widely-occurring group of intrusive felsic igneous rocks that forms at great depths and pressures under continents. Granite consists of orthoclase, plagioclase quartz, hornblende, biotite, muscovite and minor accessories such as magnetite, garnet, zircon and apatite minerals. Rarely a pyroxene is present. Ordinary granite always carries a small amount of plagioclase, but when this is absent the rock is referred to as alkali granite. An increasing proportion of plagioclase feldspar causes granite to pass into granodiorite. A rock consisting of equal proportions of orthoclase and plagioclase plus quartz may be considered a quartz monozonite. A granite containing both muscovite and biotite micas is called a binary granite.

The word granite comes from the Latin granum, a grain, in reference to the grained structure of such a crystalline rock.

Granite occurs as stock-like masses and as batholiths often associated with mountain ranges and frequently of great extent. Granite has been intruded into the crust of the Earth during all geologic periods, except perhaps the most recent; much of it is of Precambrian age. Granite is widely distributed throughout the Earth.

Because of its hardness and comparative cheapness in relation to marble, granite is often used to make kitchen countertops. A granite countertop can be cut in any shape, and it is virtually unscratchable. Very hot pots must not be placed onto it though, because the temperature differential could possibly crack the granite.

Average density: 2750 kg/m3 (range 1741 to 2800)

See also: list of minerals




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