How does Extrusive Igneous rock form?

Answer 1

Extrusive igneous rocks, also known as volcanic rocks, form from the rapid cooling and solidification of molten rock (magma) that erupts onto the Earth's surface. Here’s a step-by-step overview of the process:

1. Magma Generation: Magma forms in the Earth's mantle due to the melting of pre-existing rocks. This can occur due to various factors, including increased temperature, decreased pressure, and the addition of volatiles like water.

2. Eruption: When the pressure from the magma builds up, it can erupt through volcanic vents. This eruption can occur explosively or effusively, depending on the viscosity of the magma and the amount of gas it contains.

3. Lava Flow: Once the magma reaches the surface, it is referred to as lava. The lava can flow out of the volcano and spread across the landscape. The flow can take various forms, including sheets, plateaus, or more viscous formations.

4. Cooling and Solidification: As the lava comes into contact with the relatively cooler air or water at the surface, it begins to cool rapidly. The quick cooling prevents the formation of large crystals, resulting in a fine-grained or glassy texture typical of extrusive rocks.

5. Formation of Rock Types: The composition of the lava (which can vary in terms of silica content) will influence the kind of extrusive igneous rock that forms. Common types include:

   • Basalt: Low in silica, dark-colored, and typically forms from fluid lava flows.
   • Rhyolite: High in silica, light-colored, and tends to form from more viscous lava eruptions.
   • Pumice: Volcanic glass that forms when lava cools quickly with trapped gas bubbles, resulting in a light, porous texture.

6. Post-Eruption Processes: After the lava cools and solidifies, it can undergo further weathering and erosion or may be subject to additional volcanic activity.

In summary, extrusive igneous rocks form when lava erupts from volcanoes, cools quickly at the Earth's surface, and crystallizes into solid rock.

Answer 2

How does Intrusive Igneous rock form?

Answer 3

Intrusive igneous rocks, also known as plutonic rocks, form from the slow cooling and solidification of magma beneath the Earth's surface. Here’s a detailed explanation of the process:

1. Magma Generation: Intrusive igneous rocks begin with the generation of magma in the Earth's mantle or lower crust. This magma forms as a result of melting pre-existing rocks due to increased temperature, decreased pressure, or the introduction of volatiles.

2. Magma Intrusion: The molten magma, being less dense than the surrounding solid rock, rises through the crust. During its ascent, it may encounter cooler rock formations, where it can either cause melting of surrounding rock or migrate into existing rock formations, leading to the formation of intrusions, which can be large bodies of magma called plutons or smaller formations called dikes and sills.

3. Cooling and Crystallization: As the magma is trapped beneath the surface, it cools slowly over long periods of time (often thousands to millions of years). This slow cooling allows the minerals within the magma to crystallize and grow into larger crystals, which is a defining characteristic of intrusive igneous rocks.

4. Formation of Rock Types: The composition of the magma also influences the type of intrusive igneous rock that forms. Common types include:

   • Granite: Composed mainly of quartz, feldspar, and mica; this is a coarse-grained rock rich in silica.
   • Diorite: Intermediate in composition between granite and gabbro, often with a mix of light and dark minerals.
   • Gabbro: Lower in silica and rich in iron and magnesium; this rock is dark-colored and coarse-grained.

5. Exposure of Intrusive Rocks: Over time, erosion and tectonic activity may expose these intrusive rocks at the surface. Because they are formed deep within the Earth, they often resist weathering and can become prominent features in the landscape, such as mountain ranges or exposed rock formations.

6. Post-Evolution Processes: Intrusive rocks may also be transformed by processes such as metamorphism, where they can change under heat and pressure without melting, or by being uplifted due to tectonic forces.

In summary, intrusive igneous rocks are formed from magma that cools slowly beneath the Earth's surface, resulting in the development of large, visible crystals, and are typically exposed through geological processes over time.