B.12. Rocks
A rock is an aggregate of one or more minerals. There are the following types of rocks –
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Igneous Rocks |
An igneous rock forms out of magma and lava from the interior of the earth, also known as primary rock. Eg. Granite, Gabbro, Basalts. |
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Sedimentary Rocks |
Rocks (igneous, sedimentary and metamorphic) of the earth’s surface are exposed to denudational agents and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits through compaction turn into rocks. This process is called lithification. Eg. Sandstone, coal, limestone, chert, etc. |
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Metamorphic Rocks |
These rocks form under the action of pressure, volume, and temperature (PVT) change. Metamorphism occurs when rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks or the underlying rocks are subjected to great amounts of pressure by overlying rocks. Metamorphism is a process by which already consolidated rocks undergo recrystallization and reorganization of materials within the original rocks. Eg. Granite, syenite, slate schist, etc. Rocks do not remain in their original form for long but may undergo transformation. The Rock cycle is a process through which old rocks are transformed into new ones. |