Granite

It belongs to the intrusive rock in acidic (SiO2>66%) magmatic rocks, which is the most common type of rock in this class, mostly consisting of light flesh red, light gray, gray white, etc. Medium to coarse grained, fine-grained structure, blocky structure. Some are patchy structures, spherical structures, and gneissic structures. The main minerals are quartz, potassium feldspar and acid plagioclase, and the secondary minerals are Biotite, Amphibole, and sometimes a small amount of pyroxene. There are many kinds of accessory minerals, such as Magnetite, sphene, zircon, Apatite, Tourmaline, fluorite, etc. The quartz content is the highest among various magmatic rocks, ranging from 20-50%, with a few reaching 50-60%. The content of potassium feldspar is generally higher than that of plagioclase, and the ratio between the two is often two-thirds of the total amount of feldspar and one-third of plagioclase. Potassium feldspar in granite is mostly light flesh red, and there are also gray white and gray. Gray white potassium feldspar and plagioclase are often difficult to distinguish on hand specimens. At this point, we need to carefully observe the twin crystal characteristics of these two types of feldspars, because plagioclase has polycrystalline twin crystals. When rotating the specimen, regular alternating light and dark clusters can be seen on the plagioclase crystal, while potassium feldspar is a card twin crystal, manifested as two half crystals with different brightness levels.
Granite can also be further named according to the type of dark mineral, for example, dark mineral is mainly Biotite, which can be called Biotite granite, which is a common type of granite. For example, Biotite and Muscovite, whose contents are nearly equal, can be called two mica granite; if the dark mineral is mainly Amphibole, it is called hornblende granite; if the dark mineral is mainly pyroxene, it is called pyroxene granite; if there is almost no dark mineral, it can be called white granite.