Describe the main types off rocks. How the different types
of rocks formed ?
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Answer Posted / tushardutt pandey
A rock is any large massif the harder potion of the earth’s crust- in word we ca say that one if the skid materials . in the some case it consists of only a single mineral but generally of several minerals. A rock however dies not normally have a definite chemical composition as a mineral does
The rocks may be classified into four main types according to the way in which they have been forms as follows.
(1) Stratifies or Sedimentary Rocks:- There are the rocks which have been laid down in beds or layers(strata) by wind, running water or the seas.. These rocks are important in many ways as 75% part of the earth is made up of these rocks
Formation :-Plants and animals might sometimes have been buried and their hard part might left therein. Lather in the sediments were raised by earth-quakes into dry land. These ‘remains’ one knows as “fossils”. We can side this type of rocks into 3 groups.
i. Alluvium which are still firmed by rivers
ii. Young soft rocks which are not subject to great earth-quakes or mountaian-bulding movement oil is found in such rocks
iii. Old hard rocks which have not been folded bent and cracked by many earth-quakes occurred and they often raised into high mountains. Amongst the soft rocks, we usually find hard bands which gave rise to water-falls etc
(2) Igneous Rocks this type of rocks are also known as fiery rocks are formed due to interior heat if the earth. More rocks are if two types
i. Volcanic rocks These are the rocks which reach the surface in Volcanoes. In other countries the greate areas if rock in the Deccan around Bombay have originated in this way
ii. Thore rocks . There are the rocks which moved under-ground but became solid before they reached the surface A good example of these rocks is Granite. Such rocks are generally hard and resist weathering.
(3) Meteamorphic Rocks This means the rocks which have changed their forms. We know that earth-quake bend and fold the earth’s crust and gradually build up great mountains. In the process the rocks ate changed and hardened. Other rocks become buried by the fresh layers piled in the top of heat in the lower part of the earth’s crust. We all know that if we take a piece of clay and bake if , the brick which results is quite different from the clay. This is a the rocks might have altered far more. Therefore, it is not possible to say what the shape and composition of original rock. We call such rocks as metamorphic rocks. It takes a pretty long time to get changed. Some if the areas of crystalline rocks were firmed ages and ages ago and have remained unchanged ever since
In our country, the Deccan in a nice example of this type of rocks.
(4) Organic Rocks These rocks are formed of the remains by or of, animals or plants(organisms). Coal is an organic rock which is formed from the remains of forests which have been formerly submerged and later on buried. Mineral oils are also formed its load of mud in the sea or a lake.
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