Granite ( /ˈɡrænɨt/) is a common widely occurring type of intrusive, felsic, igneous rock which is granular and crystalline in texture. This rock consists mainly of quartz, mica, and feldspar. Occasionally some individual crystals (phenocrysts) are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is sometimes known as a porphyry. Granites can be pink to gray in color, depending on their chemistry and mineralogy. By definition, granite is an igneous rock with at least 20% quartz by volume. Granite differs from granodiorite in that at least 35% of the feldspar in granite is alkali feldspar as opposed to plagioclase; it is the alkali feldspar that gives many granites a distinctive pink color. Outcrops of granite tend to form tors and rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite is usually found in the continental plates of the Earth's crust.
Granite is nearly always massive (lacking internal structures), hard and tough, and therefore it has gained widespread use as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3-6 • 1019 Pa·s. Melting temperature is 1215 - 1260 °C.
The word granite comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a crystalline rock.
Granitoid is a general, descriptive field term for light-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids.
Famous quotes containing the word granite:
“Mans own youth is the worlds youth; at least he feels as if it were, and imagines that the earths granite substance is something not yet hardened, and which he can mould into whatever shape he likes.”
—Nathaniel Hawthorne (18041864)
“We placed the wreaths upon the splended granite sarcophagus, and at its feet, and felt that only the earthly robe we loved so much was there. The pure, tender, loving spirit which loved us so tenderly, is above usloving us, praying for us, and free from all suffering and woeyes, that is a comfort, and that first birthday in another world must have been a far brighter one than any in this poor world below!”
“I make myself this time
Of wood or granite or lime
A wall too hard for crime
Either to breach or climb....”
—Robert Frost (18741963)