Describe the formation of igneous, sedimentary, and metamorphic rocks?
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How the three types of rocks form is due to the rock cycle, where rocks are continually renewed.
Igneous rocks are formed when magma cools and crystallises. It can be formed underground or above it. Therefore, igneous rocks can be fine- (rhyolite) or large-grained (granite).
Over time, due to the effects of weathering, rock fragments are compressed and form rocks with bands that clearly define fragments of different sizes. That is one way that sedimentary rocks are formed. The other way is the organic way, where fossils of dead plants and animals give out carbonate minerals that, through chemical reaction, form limestone. The third method is the chemical method, when saturated solutions precipitate.
Metamorphorphic rocks are formed by the intense heat and pressure released in the mantle that causes rocks to bend. Because of this bending and buckling, rocks subduct and are melted in the mantle, which rise upon heating and cool again to form igneous rocks.
Date of comment: Tue, Jul 28th 2009
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