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How are extrusive and intrusive rocks formed?

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NCERT Solutions for Class 7 Social Science
Geography Chapter 2 Inside Our Earth
Question 1(iv) Page No. 10
NCERT Academic Session 2023-2024

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  1. Formation of Extrusive and Intrusive Rocks:

    Extrusive Rocks:
    – Formation: Result from rapid cooling of lava on the Earth’s surface during volcanic eruptions.
    – Cooling Rate: Quick cooling leads to fine-grained or glassy textures.
    – Examples: Basalt and obsidian are common extrusive rocks.

    Intrusive Rocks:
    – Formation: Formed from slow cooling of magma beneath the Earth’s surface.
    – Cooling Rate: Slow cooling results in coarse-grained textures.
    – Examples: Granite and diorite are typical intrusive rocks.

    Distinct cooling rates influence textures, creating differences between extrusive and intrusive rock types.

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