Granite is typical of a larger family of granitic rocks, or granitoids, that are composed mostly of coarse-grained quartz and feldspars palomillo varying proportions. These properties have made granite a widespread construction stone throughout human history.
The word “granite” comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a completely crystalline rock. The alkali feldspar in granites is typically orthoclase or microcline and is often perthitic. The plagioclase is typically sodium-rich oligoclase. True granites are further classified by the percentage of their total feldspar that is alkali feldspar.
Another aspect of granite classification is the ratios of metals that potentially form feldspars. The average density of granite is between 2. C at a few hundred megapascals of pressure. Granite has poor primary permeability overall, but strong secondary permeability through cracks and fractures if they are present. The medium-grained equivalent of granite is microgranite. The extrusive igneous rock equivalent of granite is rhyolite. Granitic rock is widely distributed throughout the continental crust.
Felsic magmas are thought to form by addition of heat or water vapor to rock of the lower crust, rather than by decompression of mantle rock, as is the case with basaltic magmas. Early fractional crystallisation serves to reduce a melt in magnesium and chromium, and enrich the melt in iron, sodium, potassium, aluminum, and silicon. Further fractionation reduces the content of iron, calcium, and titanium. The presence of granitic rock in island arcs shows that fractional crystallization alone can convert a basaltic magma to a granitic magma, but the quantities produced are small. The composition and origin of any magma that differentiates into granite leave certain petrological evidence as to what the granite’s parental rock was. The final texture and composition of a granite are generally distinctive as to its parental rock. For instance, a granite that is derived from partial melting of metasedimentary rocks may have more alkali feldspar, whereas a granite derived from partial melting of metaigneous rocks may be richer in plagioclase.