Extrusive

Definition

Extrusive refers to igneous rocks that are formed from lava that cools and solidifies quickly on the Earth's surface. This rapid cooling typically results in fine-grained textures because there isn’t enough time for large crystals to form, making extrusive rocks distinct in their appearance and composition compared to their intrusive counterparts, which cool slowly beneath the surface.

5 Must Know Facts For Your Next Test

1. Extrusive rocks can be classified into various types based on their mineral composition, such as basalt and rhyolite.
2. These rocks often have features like vesicles, which are small holes formed by gas bubbles escaping during solidification.
3. Extrusive igneous processes are commonly associated with volcanic activity, including eruptions and lava flows.
4. The rate of cooling in extrusive rocks can influence their texture, leading to variations like glassy or aphanitic textures.
5. Many extrusive rocks are found at or near tectonic plate boundaries where volcanic activity is prevalent.

Review Questions

• Compare and contrast extrusive and intrusive igneous rocks in terms of formation and texture.
  • Extrusive igneous rocks form from lava that cools quickly on the Earth's surface, leading to fine-grained textures due to rapid solidification. In contrast, intrusive igneous rocks form from magma that cools slowly beneath the surface, resulting in larger crystals. This fundamental difference in cooling rates explains why extrusive rocks typically have a glassy or aphanitic texture while intrusive rocks often exhibit a coarse-grained texture.
• Evaluate the role of volcanic activity in the formation of extrusive igneous rocks and its impact on surrounding environments.
  • Volcanic activity plays a crucial role in the formation of extrusive igneous rocks as it involves the eruption of magma onto the Earth's surface, which then cools to create these rocks. The impact on surrounding environments can be significant; eruptions can reshape landscapes, create new landforms like islands and plateaus, and even affect climate patterns temporarily through ash clouds. Furthermore, volcanic eruptions can enrich soil fertility in areas where lava has solidified, promoting plant growth.
• Analyze how the mineral composition of extrusive igneous rocks influences their physical properties and uses in construction.
  • The mineral composition of extrusive igneous rocks directly influences their physical properties such as hardness, durability, and appearance. For example, basalt is dense and strong, making it ideal for construction materials like aggregate in concrete. Other extrusive rocks like pumice are lightweight and porous, often used for insulation or as a lightweight aggregate. Understanding these properties allows engineers and architects to select appropriate materials based on the demands of construction projects.

Related terms

Volcanic: Related to or produced by volcanoes, volcanic rocks are primarily composed of materials ejected during volcanic eruptions.

Pumice:

A light, porous volcanic rock that forms when lava cools rapidly and gas bubbles are trapped within, resulting in a frothy texture.

Basalt:

A common extrusive igneous rock that is dark-colored and rich in iron and magnesium, often formed from the rapid cooling of lava at the Earth's surface.