A rock is a solid cumulative of minerals located in the earth's lithosphere.
They are generally classified into igneous, sedimentary, and metamorphic rocks, on the basis of their mineral, chemical, and textural composition.
While studying the characteristics of these rocks, it is essential to be aware about the processes that are responsible for their formation.
Igneous Rocks Igneous rocks are created when molten magma cools down. Plutonic or intrusive rocks come into being when magma cools and crystallizes gradually inside the earth's crust. Volcanic or extrusive rocks are formed when the magma reaches the surface either as lava or as fragmental ejectiles.
Though rocks have been classified into igneous rocks, sedimentary rocks, and metamorphic rocks, there are no distinct lines between them.This could even be the case when the K-Ar and Ar-Ar analyses yield "dates" compatible with other radioisotopic "dating" systems and/or with fossil "dating" based on evolutionary assumptions. Furthermore, there would be no way of knowing, because the Ar not from radioactive decay, except of course by external assumptions about the ages of the rocks. The knowledge about these rocks is crucial, especially, during construction-related activity.Metamorphic Rocks Metamorphic rocks form when rocks undergo metamorphosis/changes due to heat and pressure.