Basic Introduction To Granite

Granite is an intrusive rock among acidic (SiO2>66%) magmatic rocks. This is the most common type of rock in this category, mostly light flesh red, light gray, and off-white. Medium-coarse, fine-grained structure, block structure. There are also patchy structures, spherical structures, and gneiss-like structures. The main minerals are quartz, potash feldspar and acid plagioclase, and the secondary minerals are biotite, hornblende, and sometimes a small amount of pyroxene. There are many types of accessory minerals, the common ones are magnetite, sphene, zircon, apatite, tourmaline, fluorite and so on. Quartz content is the largest among various magmatic rocks, and its content can range from 20-50%, and a few can reach 50-60%. The content of potash feldspar is generally more than that of plagioclase. The relationship between the two contents is often that potash feldspar accounts for two-thirds of the total feldspar, plagioclase occupies one-third, and potash feldspar is more in granite. It is light flesh red, but also gray and gray. Off-white potash feldspar and plagioclase are often difficult to distinguish on hand specimens. At this time, we must carefully observe the double crystal characteristics of these two feldspars, because plagioclase has double crystals. When rotating the hand specimens, we can see that there are regular light and dark aggregates on the plagioclase crystals, and potassium feldspar It is a cassette double crystal, showing two halves of crystals with different brightness.