TYPES OF ROCKS

TYPES OF ROCKS

TYPES OF ROCKS

Types of Rocks

SEDIMENTARY

Sedimentary rocks are formed by consolidation and cementation of the sediments deposited under water. Typical sedimentary rocks are sandstones, limestone and shale.
The formation of sedimentary rocks place in three stages

Weathering and ErosionDuring weathering and erosion, the preexisting rocks and their constituent minerals are broken down. The material thus produced is called the sediment. The sediments are usually transport and deposited in area of accumulation by the action of water or less frequently by glacial and wind action. During transportation, the sediments are roughly sorted and deposited according to size , bigger rocks fragments, such as gravel, settle first, sands are next in order and clay are deposited in the last. The minerals which are dissolved by the water travel in solution.

SedimentationThe process of accumulation of sediments at a site of deposition is called sedimentation. The material carried in solution precipitates and accumulates. Sedimentation is the intermediate stage in the formation of sedimentary rocks.

Lithification and DigenesisLithification is a process by which soft and loose sediments are converted into hard and firm rocks. This process is also called consolidation. During this process many physical and chemical changes take place within the sediment. Such changes are called diagenetic changes and the process is described as diagenesis.

IGNEOUS

As a name indicates the class of rock constitutes material that have crystallized form a previously molten condition with regard to made of occurrence.
It is further divided into two types

Intrusive RocksThe rocks that are crystallized within the earth are known as intrusive rocks.
Extrusive RocksVolcanic rocks formed by cooling of molten material at the surface are called extrusive rocks.

the consolidated fragmental products of volcanic eruption formed still another group known as Pyroclastic Rocks.

METAMORPHIC ROCKS

Metamorphic rocks are formed when the pre-existing rocks have been changed in texture and composition by increased temperature and pressure. Typical rocks of this kind are schist and gneiss.
Strictly speaking any change which takes in a rock subsequently to its formation is metamorphism; however the parent’s tendency is to consider a metamorphism only those changes that take place under the action of heat, pressure or both. All other chances are considered as attraction or weathering.
Consequently metamorphism rocks may be defined as naturally accruing substance that has been formed form the parent rock (Igneous/sedimentary by the action of heat pressure or both).

It is further divided into two types

Contact MetamorphismResulting from the action of heat and solutions.

Dynamic MetamorphismResulting from the action of differential pressure