Types of Granite Introduction
Published:
2023-02-14
Granite is an intrusive rock in acidic (SiO2>66%) magmatic rocks, which is the most common type of rock in this category, mostly light fleshy red, light gray, off-white, etc. Medium-coarse, fine-grained, massive structure. There are also some mottled structures, spherical structures, and gneiss-like structures.
Granite is an intrusive rock in acidic (SiO2>66%) magmatic rocks, which is the most common type of rock in this category, mostly light fleshy red, light gray, off-white, etc. Medium-coarse, fine-grained, massive structure. There are also some mottled structures, spherical structures, and gneiss-like structures. The main minerals are quartz, potassium feldspar and acid plagioclase, and the secondary minerals are biotite, hornblende and sometimes a small amount of pyroxene. There are many kinds of accessory minerals, the common ones are magnetite, sphene, zircon, apatite, tourmaline, fluorite and so on. Quartz content is the most among all kinds of igneous rocks, and its content can range from 20-50%, and a few can reach 50-60%. The content of potassium feldspar is generally more than that of plagioclase, and the ratio between the two contents is usually that potassium feldspar accounts for two thirds of the total feldspar, plagioclase accounts for one third, and potassium feldspar is more in granite. It is light flesh red, but also off-white and gray. Gray-white potassium feldspar and plagioclase are often not easy to distinguish on hand specimens. At this time, we have to carefully observe the twin crystal characteristics of these two feldspars, because plagioclase has poly-sheet twin crystals, and when the specimen is turned, we can see regular light and dark poly-crystals on plagioclase crystals, while potassium feldspar It is a card-type twin crystal, showing two halves of crystals with different brightness.
Granite can also be further named according to the type of dark minerals. For example, dark minerals are mainly biotite, which can be called biotite granite, which is a common type of granite. If it is biotite and muscovite, its content is nearly equal, it can be called dimica granite, if the dark minerals are mainly hornblende, it is called hornblende granite, if the dark minerals are mainly pyroxene, it is called pyroxene Stone granite, which contains almost no dark minerals, can be called white granite.
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