ROCKS AND THE ROCK CYCLE

Rocks are the basic foundation in the study of Geology. When Earth was in the process of formation it was mere fluid but as the time passed it turned out into the solid form. The solid form of the Earth was constituted in the formation of rocks. When we study rocks we come to know that there is an unending cycle going on for the formation of the rock known as “Rock Cycle.”

ROCK CYCLE:

The rock cycle is a combination of processes by which the rocks are formed on the Earth. Rocks are not in a stable form. They are continuously changing their form, from one mineral form to the other. But it all has to start from some point. The rocks formed are of three types:

@  Igneous rocks

@  Sedimentary rocks

@  Metamorphic rocks

The starting point of the rock cycle is the magma. The scorching hot molten material present in the region of mantle and outer core (inner core is in solid form). The magma is in molten form due to the residual heat and heat produced by the radioactive decay. This heat leads to the formation of heat diapers and these heat diapers extend to form Mantle plumes. When the mantle plumes increase in size they are known as Super plumes. However, these super plumes make up magma chambers and these magma chambers due to pressure and temperature lead to venting out of magma and thus this magma is erupted onto the land releasing lave, ash and numerous gases.

BASICS OF START OF ROCK CYCLE

Formation of Igneous Rocks:

When the lava erupted from volcano cools down it forms Igneous Rocks. Igneous is a Greek word meaning Fire. The igneous rocks formed are of three types formed on the basis of the depth they are formed:

@  Intrusive/ plutonic igneous rocks:

The rocks formed well below surface of the Earth and appear to be crystallized from magma emplaced or intruded in surrounding rock. Example granite, gabbro and sodalite etc.

@  Intermediate/ hypabasal igneous rocks:

The rocks that are neither plutonic nor volcanic but intermediate between them, found at the shallow depths. Example Dolorite etc.

@  Extrusive/volcanic igneous rocks:

The rocks that are exposed on the surface of Earth due to eruption of lava and solidify are known as extrusive rocks. Example rhyolite, basalt, trachyte etc.

Formation of Sedimentary Rocks:

Sediment is a collective name for loose, solid particles that originate from:

                                                                    i.            Weathering and erosion of pre-existing rocks.

                                                                  ii.            Chemical precipitation from solutions.

The processes that involve formation of sedimentary rocks are:

A.    Weathering/ Erosion:

The physical removal of the some part of the rock takes place with the help of some agent such as water; wind etc. or the other method of distortion of the rock is by the help of chemical or mechanical weathering.

B.     Transportation:

The material that is weathered and eroded is then transported from one place to another by the help of winds, water, tectonic activity etc.

C.     Deposition:

The deposition of the unconsolidated material that is transported takes place and is settled down at some particular area and it is known as environment of deposition.

D.    Lithification:

The combined processes by which the loose eroded sediments undergo for its conversion to as sedimentary rock is called Lithification. The tight packing up of sediments with a resulting decrease in the pore spaces is known as Compaction. When the remaining pore spaces are invaded by the underground water, they can be filled up with the loose particles called as cement and the process is known as Cementation.

Formation of Metamorphic Rocks:

The rocks that are produced by the action of metamorphism on the preexisting rocks i.e. action of high temperature or pressure or may be both and converting them into texturally or mineralogically distinct new rock but not melting the pre-existing rocks are known as metamorphic rocks and the phenomenon is called as Metamorphism.

But yes if the introduction of ions from external source brings about chemical change in the newly formed rocks it is known as Metasomatism.

 Temperature, pressure, fluids and time acting upon the rocks are the top factors of metamorphism. When the effect of these factors are increased from the safe level metamorphic rocks are tend to change to magma and the cycle starts again. However, some of the metamorphic rocks if exposed on the surface are likely to change back to sedimentary rocks.

The rock cycle take hundreds of millions of years to reach to completion. It is very slow process but resulting in the lack of equilibrium in the nature.