Granite is a common type of felsic intrusive igneous rock which is granular and phaneritic in texture. The word “granite” comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock
The term ‘granite’ also applies to a group of intrusive igneous rocks with similar textures and slight variations on composition and origin. These rocks mainly consist of eldspar,quartz,mica, and amphibolemi. These form interlocking somewhat equigranular matrix of felddspar and quartz with scattered darkerbiotite mica and amphibole (often hornblende) peppering the lighter color minerals. 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 known as a granite porphyry. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. By definition, granite is an igneous rock with at least 20% quartz and up to 65% alkali feldspar 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 potassium feldspar that gives many granites a distinctive pink color.
Granite is nearly always massive (lacking any internal structures), hard and tough, and therefore it has gained widespread use throughout humanity, and more recently 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 • 10 19 Pa·s. Melting temperature is 1215–1260 °C.
Granite has poor primary permeabilitybut strong secondary permeability.