Rocks Of The Earth

The Earth’s crust is composed of rocks, which are mineral materials of the Earth. These rocks can be combinations of various mineral elements, such as silica-containing silicon and oxygen. They vary in texture, structure, colour, permeability, mode of occurrence, and resistance to denudation. Rocks are categorized into three types: Igneous rocks, Sedimentary rocks, and Metamorphic […]

The Earth’s crust is composed of rocks, which are mineral materials of the Earth. These rocks can be combinations of various mineral elements, such as silica-containing silicon and oxygen. They vary in texture, structure, colour, permeability, mode of occurrence, and resistance to denudation.

Rocks are categorized into three types: Igneous rocks, Sedimentary rocks, and Metamorphic rocks.

 

Characteristics of Igneous rocks:

  1. Crystalline structure with crystals present.
  2. Absence of layering.
  3. Lack of fossils.
  4. Typically hard and impervious.
  5. Resistance to erosion and weathering.

 

Formation Process:

Igneous rocks are formed by the cooling and solidification of molten magma expelled from beneath the Earth’s crust. As the magma approaches the surface, it encounters lower temperatures, leading to cooling and solidification, resulting in the formation of igneous rocks.

 

There are two major types of Igneous rocks:

  1. Plutonic (Intrusive) Igneous rocks: Formed inside the Earth’s crust before reaching the surface, resulting in rocks with large crystals (e.g., granite, gabbro, diorite).
  2. Volcanic (Extrusive) Igneous rocks: Formed outside the Earth’s crust due to the cooling and solidification of molten magma on the surface, leading to rocks with small crystals (e.g., basalt).

 

Characteristics of Sedimentary Rocks:

  1. Occur in layers or strata.
  2. Can be coarse, fine, soft, or hard.
  3. Lack crystalline structure.
  4. Do not contain fossils.
  5. Not resistant to erosion.

 

Formation Process:

Sedimentary rocks are formed from sediments deposited by water, wind, or ice. These sediments accumulate in layers, and over time, compression hardens them to create sedimentary rocks, which are stratified or layered.

 

There are three main types of Sedimentary rocks based on their mode of formation:

  1. Mechanically formed Sedimentary rocks: Formed from accumulated sediments of other rocks over time (e.g., sandstone, breccia, shale, clay, conglomerates).
  2. Organically formed Sedimentary rocks: Formed from the remains of living organisms, such as plants and animals. Those derived from plant remains are known as CARBONACEOUS Rocks (e.g., Coal, Peat, Lignite, Petroleum), while those from animal remains are CALCAREOUS Rocks (e.g., Limestone and Chalk).
  3. Chemically formed Sedimentary rocks: Precipitated chemically from solutions (e.g., Potash, Sodium Chloride, Nitrate, Gypsum, and Dolomite).

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