Extrusive igneous rock

Definition

Extrusive igneous rock is formed from the cooling and solidification of molten lava on the Earth's surface. These rocks typically have a fine-grained texture due to the rapid cooling that occurs when lava erupts and comes into contact with air or water, preventing large crystals from forming. Their characteristics are essential in understanding volcanic activity and the geological processes that shape the Earth's crust.

5 Must Know Facts For Your Next Test

1. Extrusive igneous rocks are typically associated with volcanic eruptions, which can create various landforms such as shield volcanoes, stratovolcanoes, and lava plateaus.
2. Common examples of extrusive igneous rocks include basalt and pumice, each with distinct properties based on their mineral composition and cooling history.
3. The rapid cooling of lava at the surface leads to a glassy appearance in some extrusive rocks, such as obsidian, which lacks any visible crystal structure.
4. Extrusive igneous rocks often contain vesicles, which are small gas bubbles formed during solidification, giving them a unique texture and appearance.
5. The study of extrusive igneous rocks helps geologists understand volcanic activity and the processes that shape the Earth's landscape over time.

Review Questions

• Compare and contrast extrusive igneous rocks with intrusive igneous rocks in terms of formation and texture.
  • Extrusive igneous rocks form from lava that cools quickly on the Earth's surface, resulting in fine-grained textures and often glassy appearances. In contrast, intrusive igneous rocks form from magma that cools slowly beneath the surface, allowing larger crystals to develop. This difference in cooling rates is key in distinguishing these two types of igneous rocks, as their textures provide insights into their formation environments.
• Discuss the role of extrusive igneous rocks in understanding volcanic processes and their impact on Earth's geology.
  • Extrusive igneous rocks are critical for understanding volcanic processes because they form directly from erupting lava. By studying these rocks, geologists can gain insights into eruption styles, magma composition, and the conditions under which volcanoes operate. The presence of different types of extrusive rocks helps scientists reconstruct past volcanic activity and assess potential hazards associated with future eruptions.
• Evaluate how the characteristics of extrusive igneous rocks contribute to their use in various applications, including construction and landscaping.
  • Extrusive igneous rocks possess unique characteristics that make them valuable for various applications. For instance, basalt's durability and strength make it an excellent material for road construction and concrete production. Similarly, pumice is lightweight and abrasive, making it useful in landscaping for soil aeration or as an aggregate in lightweight concrete. Understanding these properties allows for better utilization of extrusive igneous rocks in practical applications while also highlighting their geological significance.

Related terms

Magma: Magma is molten rock located beneath the Earth's surface, which can erupt as lava and ultimately solidify to form igneous rocks.

Volcanic rock: Volcanic rock is a type of extrusive igneous rock that forms from lava that cools quickly after being expelled during a volcanic eruption.

Aphanitic texture: Aphanitic texture refers to a fine-grained texture found in extrusive igneous rocks, where individual mineral grains are too small to be seen without a microscope.