Types of Rocks – Geography Notes PDF in English & Hindi for UPSC and Other Competitive Exams

Types of Rocks: Rocks are naturally occurring solid aggregates of minerals, mineraloids, or organic materials. They are classified into three main types based on their formation and mineral composition: igneous rocks, sedimentary rocks, and metamorphic rocks. Each type of rock has distinct characteristics and forms through different geological processes.

Types of Rocks

Here’s an overview of the three main types of rocks:

Igneous Rocks Solidified from magma and lava
Sedimentary Rocks The result of the deposition of fragments of rocks by exogenous processes
Metamorphic Rocks Formed out of existing rocks undergoing recrystallization
  1. Igneous Rocks:
    • Igneous rocks are formed from the solidification and cooling of molten rock material, either magma (beneath the Earth’s surface) or lava (on the Earth’s surface).
    • They are classified into two main categories: intrusive (plutonic) and extrusive (volcanic) rocks.
    • Intrusive Igneous Rocks: Formed beneath the Earth’s surface, they cool slowly, allowing larger mineral crystals to develop. Examples include granite and diorite.
    • Extrusive Igneous Rocks: Formed on the Earth’s surface, they cool quickly, resulting in smaller mineral crystals. Examples include basalt and pumice.
  2. Sedimentary Rocks:
    • Sedimentary rocks are created through the accumulation and compression of sediments, which may include fragments of other rocks, minerals, and organic materials.
    • They are divided into three main categories: clastic, chemical, and organic.
    • Clastic Sedimentary Rocks: Composed of mineral and rock fragments, such as sandstone, shale, and conglomerate.
    • Chemical Sedimentary Rocks: Formed from the precipitation of dissolved minerals, such as limestone (calcium carbonate) and rock salt (halite).
    • Organic Sedimentary Rocks: Comprised of organic materials, including coal and some types of limestone.
  3. Metamorphic Rocks:
    • Metamorphic rocks are created from the alteration of pre-existing rocks (igneous, sedimentary, or other metamorphic rocks) through heat, pressure, or chemically active fluids.
    • They are often classified based on the degree of metamorphism and foliation (layering).
    • Examples of metamorphic rocks include marble (from limestone), schist, and slate.

It’s important to note that rocks are not static, and they can undergo changes over geological time due to the Earth’s dynamic processes. For example, an igneous rock exposed to high temperatures and pressures can transform into a metamorphic rock, or sedimentary rocks can become buried and compacted to form new sedimentary rocks.

Understanding the types of rocks and their properties is essential in geological and environmental studies, as it provides insights into the Earth’s history, geological processes, and the formation of various landscapes and natural resources.

Download Types of Rocks Notes PDF in Hindi

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By Team Learning Mantras