MCQ Detailed View

The Earth’s crust is made up of different types of rocks, classified based on how they are formed. Rocks that originate from molten material (also known as magma or lava) within or on the surface of the Earth are called igneous rocks.

How Igneous Rocks Are Formed:

Inside the Earth, intense heat melts solid rock into magma. When this molten material cools and solidifies, it forms igneous rocks. The process can occur:

1. 
   

   Beneath the surface: Magma cools slowly deep underground, forming intrusive igneous rocks like granite, with large, visible crystals.

   
   


2. 
   

   On the surface: When magma erupts from a volcano as lava and cools rapidly, it forms extrusive igneous rocks like basalt or pumice, which have smaller crystals or porous textures.

   
   

Why Other Options Are Incorrect:

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  Sedimentary rocks: Formed from compressed layers of sand, mud, and organic material over long periods (e.g., sandstone, limestone).

  
  


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  Schist rock: A type of metamorphic rock, formed from existing rocks under heat and pressure, not directly from magma.

  
  


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  Metamorphic rocks: Result from transformation of existing rocks (igneous or sedimentary) due to extreme heat, pressure, or chemical processes, not directly from molten material.

  
  

Key Facts:

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  Igneous rocks make up about 95% of the Earth’s crust, though much of it lies beneath oceans and sediments.

  
  


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  The word igneous comes from the Latin word “ignis”, meaning fire, reflecting its fiery origins.

  
  


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  Examples: Granite, Basalt, Obsidian, Diorite, Pumice.

  
  

Thus, the correct answer is:

✅ Igneous rock — the type of rock formed directly from molten (fire) material within or on the Earth’s surface.