The word granite has been derived from the Latin word ‘granum’ meaning grain. Granite is an intrusive, igneous rock with a granular and phaneritic texture, occupying 70-80% of the Earth’s crust. It is plutonic in origin, implying that it was formed deep underground. This rock is primarily composed of interlocking crystals of alkali feldspar (65% by volume), quartz (20% by volume), mica, amphiboles and other minerals. Depending on the mineral composition, the colour of granite can be red, pink, grey or white with dark mineral grains visible to the unaided eye. Granite is a hard and tough rock with an average density between 2.65 and 2.75 g/cm.
Till now, granite is know to occur only on Earth where it is found abundantly in all continents as part of the continental crust. This rock is found either in small, stock like masses spread over an area less than 100 km² or as batholiths which are part of orogenic mountain ranges. Granite usually forms the base underground rock with other continental and sedimentary rocks resting over it. Granite also occurs in lacoliths, dikes and sills. Other rock variations, similar in composition to granite, are alpites and pegmatites. Alpites with finer grain size than granite, occur at the margins of granitic intrusions. Pegmatites with coarser grains than granite often share locations with granite deposits.
There are several controversial theories regarding the origin of granite. The most widely propagated ones are the magmatic theory and the hypermetamorphic theory. According to the magmatic theory, plutonic rocks like granite, which are often found associated with mountain ranges, originated from magma. It is believed that during the formation of mountains, when one continental edge subdues another one below it, the pressure and frictional forces generated by this phenomenon is sufficient to melt the rocks underneath the subdued continental edge. This melted rock or magma seeps up in the form of large globules or plutons. It takes an extremely long time for the plutons to arrive at the surface of the earth and to be converted into a surface rock, the pluton must be eroded by the weathering forces acting on the ground. This could be one of the processes by which granite formation takes place. The hypermetamorphic theory, however, disregards the magmatic theory and instead propagates that granite is the result of melting and re-crystallization of sedimentary rock instead of magma. However, as of yet, the precise method of granite formation, is still under research till a conclusive proof of formation of this rock is attained.
Granite is endowed with all the desirable properties required to use it as a dimension stone. It is hard and durable enough to resist abrasion and bear significant weight. It is also considerably inert in nature and can be polished to achieve a brilliant finish. Hence, this stone is used for a variety of structural and decorative purposes. Both the ancient world and the modern one bear evidence of the importance of granite as a building material. The Brihadeeswarar Temple in Tanjore, India, is an example of an architectural wonder built entirely of granite. The Red Pyramid of Egypt, an ancient sarcophagus in the Great Pyramid of Giza and other architectural masterpieces of Egypt, have granite as one of the important construction materials. Today, Granite is commonly used in the making of roads, pavements, monuments, public buildings and bridges. Aberdeen in Scotland is often referred to as the ‘Granite City’ due to the extensive use of granite in the construction work of the city. In case of indoor applications, granite is a great choice for manufacturing kitchen countertops, floor tiles, stair treads, etc. The material also finds use in building gravestones and memorials. The crushed form of granite is used as fillings for various construction activities.
Granite is mined worldwide but the most exotic colours are obtained from granite deposits in Brazil, India, China, Finland, South Africa and North America. Granite mining is a capital and labour intensive process. Chunks of granite are extracted from deposits by cutting or blasting procedures. Specialized slicing machines are used to cut the extracted chunks of granite into transportable slabs which are then packed and transported via rail or shipping services. China, Brazil and India are some of the leading granite producers in the world.
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