Igneous rock

Welcome to the second episode of the Petrology course! Building upon our introduction to petrology, this episode focuses on igneous rocks, one of the three major rock types. We will explore how igneous rocks form from the cooling and solidification of molten rock (magma or lava). The episode will cover the classification of igneous rocks based on their texture (grain size) and composition (mineral content), distinguishing between intrusive (plutonic) and extrusive (volcanic) rocks. You'll learn how these characteristics provide clues about the cooling history and environment in which the rocks formed. This episode forms a necessary foundation for understanding sedimentary and metamorphic rocks, to be presented next.

Check your understanding

These are the same multiple-choice questions you will see in the Quiz section after you listen to the episode. Use them here to preview or review the answers.

How are igneous rocks formed?

  1. From the accumulation of sediments.
  2. From the cooling and solidification of molten rock.
  3. From the alteration of existing rocks under high pressure and temperature.
  4. From the precipitation of minerals from water.
  5. From organic material.
  6. From wind erosion

What is the difference between intrusive and extrusive igneous rocks?

  1. Intrusive rocks are formed from lava, while extrusive rocks are formed from magma.
  2. Intrusive rocks have large crystals, while extrusive rocks have small crystals.
  3. Intrusive rocks are formed at the Earth's surface, while extrusive rocks are formed deep underground.
  4. Intrusive rocks are always felsic, while extrusive rocks are always mafic.
  5. Intrusive rocks contain fossils.
  6. There is no difference

What is the term for molten rock found beneath the Earth's surface?

  1. Lava
  2. Magma
  3. Sediment
  4. Mineral
  5. Rock
  6. Crystal

Which of the following is an example of a coarse-grained, intrusive igneous rock?

  1. Basalt
  2. Obsidian
  3. Granite
  4. Andesite
  5. Rhyolite
  6. Pumice

What does the texture of an igneous rock tell us?

  1. The exact age of the rock.
  2. The rate at which the molten rock cooled.
  3. The specific minerals present in the rock.
  4. The original location of the rock.
  5. The type of volcano it came from.
  6. Its color

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