Geography [3 Mark Question Answer]

Regional metamorphism When metamorphism of bed rocks takes place over a very large area, it is called Regional metamorphism. It is usually caused by the movement of the earth’s crust. Contact metamorphism when it takes place over a small area, it is called Local Metamorphism or Contact Metamorphism. It commonly occurs when hot magma comes in contact with other rocks.

During the formation of sedimentary rocks, the sediments are deposited in waterbodies and get sorted out according to their size. The sediments accumulate in different layers or strata arranged one above the other. Each layer or stratum has particles of given size. In sedimentary rocks each layer or stratum has particles of a given size. Therefore, sedimentary rocks are also called stratified rocks.

The composite zone inhabited by most living creatures is called biosphere. It includes a part of the atmosphere, the hydrosphere and a part of the lithosphere. All three layers are essential for life to exist.
As lithosphere is only a small part of the biosphere, therefore, man’s habitat is the biosphere and not the lithosphere in the true sense.

A rock can be defined as “an aggregate of minerals that forms a more or less definite unit of the earth’s crust”. A rock does not possess a definite composition like that of a chemical compounds, but is usually a mixture of various minerals.
The bulk of rocks is made up of silica or quartz and feldspar. Feldspar are composed of silica, aluminium, potassium and sodium or calcium. Some rocks are composed of grains cemented together, while several other are crystalline, compact or even glass-like.
All material (whether hard like stone or sand) of which the crust of the earth is composed are called rocks e.g, stone, clay, lava, sand, chalk, salt, coal marble etc.

There are three types of this type of rocks :

1. Mechanically formed rocks : Denudation of rocks by agents of change results in layers of sedimentary rocks by mechanism.
2. Chemically formed rocks : These are formed by evaporation of calcarious water and accumulated along lake and lagoon beds, e.g. gypsum and rock salt.
3. Organically formed rocks : These are formed by deposition of dead plants and animals e.g. limestone rock (or Calcareous rock) lignite, bituminous and anthracite coal are carbonaceous rocks formed by compression of vegetation under the layers of sedimentary rocks. In the same way petroleum in between the sedimentary rocks is the result of zurasic age dinosaurs e.g. shale rock, containing oil.

The rocks contain minerals in the form of ores, but minerals do not contain rocks. Sedimentary rocks contain fossil fuels like coal and petroleum etc, igneous rocks are rich in minerals like copper, gold, iron etc, metamorphic rocks contain valuable building stones like marble and garnet, feldspar etc. Rocks have no definite chemical composition, while minerals have particular chemical composition.