Granite – Properties and Usage
Granite – Properties and Usage
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark gray or even black, depending on their chemistry and mineralogy. Outcrops of granite tend to form tors, and rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels.
Granite is an igneous rock and is formed from magma. Granitic magma has many potential origins but it must intrude other rocks. Most granite intrusions are emplaced at depth within the crust, usually greater than 1.5 kilometers and up to 50 km depth within thick continental crust. The origin of granite is contentious and has led to varied schemes of classification. Classification schemes are regional; there is a French scheme, a British scheme and an American scheme. This confusion arises because the classification schemes define granite by different means. Generally, the ‘alphabet-soup’ classification is used because it classifies based on genesis or origin of the magma.
Ancient Uses of Granites
Granite is nearly always massive (lacking internal structures), hard and tough, and therefore it has gained widespread use as a construction stone. The Red Pyramid of Egypt, named for the light crimson hue of its exposed granite surfaces, is the third largest of Egyptian pyramids. Menkaure’s Pyramid, was constructed of limestone and granite blocks. The Great Pyramid of Giza contains a huge granite sarcophagus fashioned of “Red Aswan Granite.” The mostly ruined Black Pyramid dating from the reign of Amenemhat III once had a polished granite pyramidion or capstone, now on display in the main hall of the Egyptian Museum in Cairo.
Many large Hindu temples in southern India were made of granite. There is a large amount of granite in these structures. They are comparable to the Great Pyramid of Giza
Granites Use in Current age
Granite has been extensively used as a dimension stone and as flooring tiles in public and commercial buildings and monuments. With increasing amounts of acid rain in parts of the world, granite has begun to supplant marble as a monument material, since it is much more durable. Polished granite is also a popular choice for kitchen countertops due to its high durability and aesthetic qualities.
Engineers have traditionally used polished granite surfaces to establish a plane of reference, since they are relatively impervious and inflexible. Sandblasted concrete with a heavy aggregate content has an appearance similar to rough granite, and is often used as a substitute when use of real granite is impractical. Because of the particular rarity of the granite, the best stones can cost as much as US$1,500.
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