Paleogeology

Paleogeology, Paleoclimate, in relation to Evolution of Life on Earth

granite

close-up images of various granitesGranite is typically a medium to coarse grained felsic, intrusive igneous rock (plutonic) that is usually pink to dark gray, sometimes black, depending on its chemistry and mineralogy. Granites are the commonest basement rocks of the continental crust, many dating from the Precambrian.

In some granites, individual crystals are larger than the groundmass (porphyrys). Granites primarily comprises orthoclase and plagioclase feldspars, quartz, hornblende, muscovite and/or biotite micas, with minor accessory minerals such as magnetite, garnets, zircon and apatite. Rarely, a pyroxene is present. Very rarely, iron-rich olivine, fayalite, occurs.

Granites are classified according to the QAPF diagram for granitoids and phaneritic foidolites (plutonic rocks) that compares the percentages of quartz, alkali feldspar (orthoclase, sanidine, or microcline) and plagioclase feldspar.

As a plutonic rock, granite is often exposed in weathered tors, dykes and as massive batholiths.

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