Physical Geology

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Intrusive igneous rock

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Physical Geology

Definition

Intrusive igneous rock is a type of rock that forms from the slow crystallization of magma beneath the Earth's surface. This process occurs over long periods, allowing large crystals to develop, which results in a coarse-grained texture. The characteristics of intrusive igneous rocks can provide insights into the conditions under which they formed and the type of magma involved.

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5 Must Know Facts For Your Next Test

  1. Intrusive igneous rocks typically exhibit a coarse-grained texture due to the slow cooling process that allows large crystals to form.
  2. Common examples of intrusive igneous rocks include granite, diorite, and gabbro, each characterized by different mineral compositions.
  3. The formation of intrusive igneous rocks occurs in various geological settings, including volcanic arcs, continental crust, and mid-ocean ridges.
  4. Intrusive rocks often contain features like xenoliths, which are fragments of surrounding rock that have been incorporated into the magma.
  5. Because they cool slowly, intrusive igneous rocks are often less susceptible to weathering compared to their extrusive counterparts.

Review Questions

  • Compare and contrast intrusive igneous rocks with extrusive igneous rocks in terms of formation and texture.
    • Intrusive igneous rocks form from magma that cools slowly beneath the Earth's surface, resulting in a coarse-grained texture with larger crystals. In contrast, extrusive igneous rocks form from lava that cools quickly on the Earth's surface, leading to a fine-grained texture with smaller crystals or a glassy appearance. The difference in cooling rates is the primary factor influencing their textures and mineral compositions.
  • Discuss how the mineral composition of intrusive igneous rocks can affect their physical properties and uses in construction.
    • The mineral composition of intrusive igneous rocks significantly influences their physical properties such as hardness, density, and color. For instance, granite, composed mainly of quartz and feldspar, is known for its durability and aesthetic appeal, making it a popular choice for countertops and buildings. On the other hand, rocks like diorite may have different applications due to variations in their strength and appearance. Understanding these properties helps in selecting appropriate materials for construction projects.
  • Evaluate the geological significance of studying intrusive igneous rocks in understanding Earth's history and processes.
    • Studying intrusive igneous rocks provides valuable insights into Earth's geological history and processes. Their formation can reveal information about past volcanic activity, magma composition, and tectonic settings. Additionally, analyzing these rocks helps geologists understand how crustal processes have shaped the Earth's surface over time. This knowledge is crucial for reconstructing past environments and predicting future geological events.

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