Primary rocks, also known as igneous rocks, are formed from solidified molten magma and are fundamental to Earth's geology. These rocks are classified into intrusive and extrusive types based on their formation process. Understanding primary rocks is essential for grasping the Earth's structure and geological processes.

Q. 4 Describe the characteristics and types of primary rocks.

Model Answer:

Introduction

Primary rocks, also known as igneous rocks, are formed directly from the cooling and solidification of magma or lava. These rocks are considered "primary" because they are the original rocks from which other rock types are derived.

Body

There are two main types of primary rocks - 

‍

• Intrusive (Plutonic) Rocks:
  • Form when magma cools slowly beneath the Earth's surface
  • Have large, visible crystals due to slow cooling
  • Examples - granite, diorite, and gabbro
• Extrusive (Volcanic) Rocks:
  • Form when lava cools rapidly on the Earth's surface
  • Have small crystals or glassy texture due to rapid cooling
  • Examples - Basalt, obsidian, and pumice

•  Pyroclastic Rocks
  • These rocks are formed from volcanic materials ejected during explosive eruptions. They include fragments of various sizes and compositions.
  • Tuff: Composed of volcanic ash and small rock fragments. It can be fine-grained or coarse-grained.
  • Volcanic Breccia: Contains larger rock fragments in a finer matrix. It is formed from volcanic debris.

‍

Some key characteristics of primary rocks include - 

• Texture - Ranges from fine-grained to coarse-grained, depending on cooling rate
• Mineral composition - Typically composed of silicate minerals
• No layering or fossils - Unlike sedimentary rocks
• Hardness - Generally harder than sedimentary rocks
• Density- Often denser than other rock types. 

Importance of Igneous Rocks

• Geological Significance-They provide information about the Earth's interior and the processes that occur beneath the surface.
• Economic Importance- Many igneous rocks are sources of valuable minerals and metals. For example, granite is widely used in construction, and basalt is used in road building.
• Soil Formation - Weathering of igneous rocks contributes to soil formation, which is essential for agriculture.

‍

Instant Mains Evaluation with SuperKalam

✅ Now that you have gone through the model answer, try practicing and writing it in your own words and evaluate it instantly with SuperKalam here - Evaluate Mains Answer instantly