Difference Between Intrusive and Extrusive Igneous Rocks
Igneous rocks are formed through the solidification of molten magma or lava. They can occur in two different settings: intrusive and extrusive. These terms refer to the location and conditions under which the rocks are formed. Here are the key differences between intrusive and extrusive igneous rocks.
1. Formation: Intrusive igneous rocks are formed when magma cools slowly beneath the Earth’s surface, resulting in the formation of large crystals. Extrusive igneous rocks, on the other hand, are formed when lava cools rapidly on the surface, leading to the formation of small crystals or glass-like texture.
2. Cooling rate: Intrusive rocks cool slowly due to the insulating properties of surrounding rocks, allowing sufficient time for larger crystals to form. Extrusive rocks cool rapidly due to exposure to air or water, resulting in the formation of small or microscopic crystals.
3. Crystal size: Intrusive rocks typically have larger crystals that are visible to the naked eye. In contrast, extrusive rocks have smaller crystals that may require the use of a microscope to be observed.
4. Texture: Intrusive rocks generally have a coarse-grained or phaneritic texture due to their slow cooling process. Extrusive rocks exhibit a fine-grained or aphanitic texture due to rapid cooling.
5. Examples: Common examples of intrusive igneous rocks include granite, diorite, and gabbro. Examples of extrusive igneous rocks include basalt, andesite, and rhyolite.
6. Composition: Intrusive rocks have a higher silica content and are often classified as either felsic or intermediate in composition. Extrusive rocks have a lower silica content and are typically classified as mafic or intermediate in composition.
7. Presence of gas bubbles: Extrusive rocks may contain gas bubbles or vesicles due to the rapid cooling process, which traps gas within the solidifying lava. Intrusive rocks, formed underground, do not have gas bubbles.
8. Surface exposure: Intrusive rocks are not visible at the surface unless they are exposed by tectonic forces or weathering and erosion processes. Extrusive rocks are commonly found at the Earth’s surface, forming volcanic features such as lava flows and volcanic cones.
9. Geological significance: Intrusive igneous rocks often form the core of mountain ranges and are associated with the formation of various minerals and ore deposits. Extrusive igneous rocks play a significant role in building volcanic islands, creating new land, and contributing to the formation of soils.
10. Economic importance: Intrusive igneous rocks, such as granite, are widely used as construction materials, dimension stones, and countertops. Extrusive igneous rocks, like basalt, are used for road construction, asphalt, and aggregates.
Questions and Answers:
1. What is the main difference between intrusive and extrusive igneous rocks?
– The main difference lies in their formation process and cooling rate.
2. How are intrusive igneous rocks formed?
– They are formed when magma cools slowly beneath the Earth’s surface.
3. How are extrusive igneous rocks formed?
– They are formed when lava cools rapidly on the surface.
4. Why do intrusive rocks have larger crystals than extrusive rocks?
– Intrusive rocks cool slowly, allowing enough time for larger crystals to form.
5. What is the texture of intrusive igneous rocks?
– They generally have a coarse-grained or phaneritic texture.
6. What are some examples of intrusive igneous rocks?
– Granite, diorite, and gabbro are common examples.
7. How do extrusive igneous rocks cool rapidly?
– They cool rapidly due to exposure to air or water on the Earth’s surface.
8. What texture do extrusive igneous rocks exhibit?
– They exhibit a fine-grained or aphanitic texture.
9. Name some examples of extrusive igneous rocks.
– Basalt, andesite, and rhyolite are common examples.
10. Do intrusive rocks contain gas bubbles?
– No, intrusive rocks do not contain gas bubbles.
11. Why do extrusive rocks sometimes have gas bubbles?
– The rapid cooling process traps gas within the solidifying lava, forming gas bubbles.
12. Can intrusive rocks be seen at the Earth’s surface?
– Intrusive rocks are usually not visible at the surface unless exposed by geological forces or weathering.
13. Where are extrusive rocks commonly found?
– Extrusive rocks are commonly found at the Earth’s surface, forming volcanic features.
14. What types of igneous rocks form the core of mountain ranges?
– Intrusive igneous rocks often form the core of mountain ranges.
15. Which igneous rocks contribute to the formation of new land?
– Extrusive igneous rocks contribute to the formation of new land by building volcanic islands.
16. Why are intrusive igneous rocks economically important?
– They are used as construction materials, dimension stones, and countertops.
17. What are some common uses of extrusive igneous rocks?
– They are used for road construction, asphalt, and aggregates.
18. Are intrusive rocks high or low in silica content?
– Intrusive rocks have a higher silica content.
19. Are extrusive rocks high or low in silica content?
– Extrusive rocks have a lower silica content.
20. How do intrusive and extrusive igneous rocks differ in geological significance?
– Intrusive rocks are associated with mineral and ore deposits and play a role in mountain formation, while extrusive rocks build volcanic landforms and contribute to soil formation.
