Question

Which of the following is an example of extrusive igneous rock?
1. Granite
2. Basalt
3. Marble
4. None of the above

Answer 1

Correct Answer - Option 2 : Basalt

The correct answer is Basalt.

• ​Basalt is a dark-colored, fine-grained, igneous rock.
• Basalt is an extrusive igneous rock formed by the rapid cooling of lava.
• Basalt is rich in iron and magnesium and is mainly composed of olivine, pyroxene, and plagioclase. 

• Igneous rocks are formed when molten material from within the Earth, called magma, cools down and solidifies forming crystals.
• They are characterized by an interlocking crystalline texture.
• Igneous Rocks mainly are of two types:
  • ​Intrusive rocks:
    • ​Intrusive (plutonic) rocks form when magma solidifies within the crust below the surface.
    • It usually cools slowly and produces large crystals. 
    • Examples of intrusive igneous rocks are diabase, diorite, gabbro, granite, pegmatite, and peridotite.
  • Extrusive rocks
    • Extrusive (volcanic) rocks form when magma erupts onto the surface of the Earth as lava flows, and usually cools quickly producing small crystals.
    • It can also erupt explosively as ash.
    • Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals.
    • Some cool so quickly that they form an amorphous glass.
    • These rocks include Andesite, Basalt, Dacite, Obsidian, Pumice, Rhyolite, Scoria, and Tuff.

• Granite: 
  • ​Granite is the most common intrusive rock in Earth’s continental crust.
  • It is familiar as a mottled pink, white, grey, and black ornamental stone. 
  • It is coarse- to medium-grained.
  • Its three main minerals are feldspar, quartz, and mica, which occur as silvery muscovite or dark biotite, or both. 
• Marble:
  • A marble is a metamorphic rock that forms when limestone is subjected to the heat and pressure of metamorphism..
  • It is composed primarily of the mineral calcite (CaCO3) and usually contains other minerals, such as clay minerals, micas, quartz, pyrite, iron oxides, and graphite.
  • Marble is usually a light-colored rock.
  • Marble is of extremely high purity with a bright white color is very useful.