distinguish between extrusive and intrusive rocks?

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Both are formed from the crystallization of minerals caused by the cooling of magma. 

Intrusive igneous rocks cooled below the surface of the planet, however, and generallydisplay larger crystals due to the increased amount of time spent at mineral crystallization temperatures from the insulating effect of surrounding material. 

Examples: granite, gabbro, diorite, peridotite. 


Extrusive rocks are formed from magma at or above the surface of the planet, and generally display smaller mineral crystals, or no crystals at all, because of the rapid cooling environment in which they form. Chemically, an intrusive and extrusive rock could be identical, the only difference being the size of the mineral crystals they contain. 

Examples: obsidian, rhyolite, pumice, scoria, basalt

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EXTRUSIVE IGNEOUS ROCK

  1. extrusive rock is formed outside the earth crust
  2. it is formed by the solidification of molten lava outside the earth crust
  3. as lava cools down quickly the extrusive rocks have a fine grained structure
  4. ex:- basalt

INTRUSIVE IGNEOUS ROCKS

  1. entrusive rock is formed inside the earth crust
  2. it is formed by the solidification of magma inside the crust
  3. as magma cools down slowly they have large grained structure
  4. ex:- granite

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Extrusive or volcanic rocks: These rocks are formed when magma breaks through the crust and reaches the surface of the earth (where it is called lava). It cools rapidly and solidifies to form rocks. The common rocks formed in this manner are basalt and obsidian.

Instrusive or plutonic rocks: These rocks are formed when magma fails to break through the crust and cools slowly under the crust  forming rocks. Because of slow cooling it solidifies into rocks with large grains of crystals. The common eg of rocks formed in this manner are granite and dolerite.

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