Rocks are found on the upper part of lithosphere. These rocks can be classified into various types search as the igneous rocks the sedimentary rocks and the Metamorphic rock. The basis of differentiating the rocks is their origin and their components with which they are formed.
1. Volcanic rocks or the igneous rocks –
These types of rocks are formed by the cooling of magma or the hot Lava present inside the surface of the earth. These are not stratified rocks that is the do not occur in strata or layers. Their extremely heart and resistance and these types of Rocks are normally crystalline in structure. On the basis of the acid content rocks are classified as acid igneous rocks and basic igneous rocks. Those rocks which have a high proportion of silica inside them are acid igneous rocks for example granite. These types of rock less than and lighter in colour as compared to the basic igneous rocks. Basic igneous rocks have a greater proportion of basic oxide and that is why they are denser and darker in colour.
On the basis of origin igneous rocks can be classified into plutonic and Volcanic rocks. Plutonic rocks and intrusive rocks and are formed at some depth inside the earth crust and are exposed to the surface due to erosion and denudation. By the Volcanic rocks are extrusive rocks and solidify on the earth surface.
2. The sedimentary rock – there was a time that stratified rocks because they are present in layer. These types of rocks are formed from sediments accumulated over long periods of time usually underwater. These types of Rock and non-crystalline and often contain fossils plants and microorganisms. They are the most Varied type of Rock in formation and they are classified according to their age.
On the basis of origin or formation sedimentary rocks can be classified into mechanically formed rocks, organically formed rocks and chemically formed rock.
Examples of sedimentary rocks are conglomerate limestone Chalk sandstone etc.
3. The metamorphic rocks- all the rocks whether igneous or sedimentary become Metamorphic or change rock under great heat and pressure particularly during intense Earth movements. Due to this the original character of these rocks may be greatly altered. For example clay becomes slate limestone becomes marble coal becomes graphite etc.