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Questions and Answers
What type of rock forms when basaltic magma mixes with granitic magmas?
What type of rock forms when basaltic magma mixes with granitic magmas?
Which rock is considered an intrusive basalt equivalent?
Which rock is considered an intrusive basalt equivalent?
What type of rock has a medium or coarse-grained texture and rarely contains quartz?
What type of rock has a medium or coarse-grained texture and rarely contains quartz?
What type of rock is formed by the end stage of magma's crystallization and contains exceptionally large crystals?
What type of rock is formed by the end stage of magma's crystallization and contains exceptionally large crystals?
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Which rock is formed when the liquid rock cools very slowly over a long period of time underground?
Which rock is formed when the liquid rock cools very slowly over a long period of time underground?
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Where are most Pegmatites found in relation to other types of rocks?
Where are most Pegmatites found in relation to other types of rocks?
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What is the most common intrusive rock in Earth's continental crust?
What is the most common intrusive rock in Earth's continental crust?
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Which intrusive igneous rock is characterized by the presence of a feldspathoid mineral like nepheline or leucite?
Which intrusive igneous rock is characterized by the presence of a feldspathoid mineral like nepheline or leucite?
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Which type of igneous rocks are formed inside the Earth?
Which type of igneous rocks are formed inside the Earth?
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What type of igneous rock is basalt?
What type of igneous rock is basalt?
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What is the main difference between intrusive and extrusive igneous rocks?
What is the main difference between intrusive and extrusive igneous rocks?
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What color is diorite typically found in?
What color is diorite typically found in?
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Which of the following is an example of an extrusive igneous rock?
Which of the following is an example of an extrusive igneous rock?
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What causes partial melting of the oceanic plate to produce a basaltic magma?
What causes partial melting of the oceanic plate to produce a basaltic magma?
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What causes the vesicular texture in some extrusive igneous rocks?
What causes the vesicular texture in some extrusive igneous rocks?
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Which type of rock can be observed with naked eyes due to the presence of visible minerals?
Which type of rock can be observed with naked eyes due to the presence of visible minerals?
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What type of texture do intrusive igneous rocks like granite and diorite have?
What type of texture do intrusive igneous rocks like granite and diorite have?
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Why does obsidian have a smooth texture with no visible grains?
Why does obsidian have a smooth texture with no visible grains?
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Study Notes
Igneous Rock Formation
- Basaltic magma mixing with granitic magmas forms andesite, a volcanic rock with intermediate composition.
- Gabbro is the intrusive basalt equivalent, containing similar minerals to basalt but crystallized underground.
Texture and Crystallization
- Rocks with a medium or coarse-grained texture, typically lacking quartz, include diorite.
- Pegmatite forms during the last stages of magma crystallization, featuring exceptionally large crystals due to slow cooling.
- Intrusive igneous rocks cool very slowly underground, allowing for larger crystal formation, exemplified by gabbro and granite.
Geological Context
- Most pegmatites are found near granite deposits, typically in the late stages of magmatic evolution.
- Granite is the most common intrusive rock in Earth's continental crust, characterized by its light color and coarse texture.
- Nepohelinite and leucite are identified in intrusive igneous rocks that contain feldspathoid minerals like nepheline, distinct from more common feldspar minerals.
Intrusive vs. Extrusive
- Intrusive igneous rocks form beneath the Earth’s surface, whereas extrusive igneous rocks form from lava that cools quickly on the surface.
- Basalt is classified as an extrusive igneous rock, typically dark in color and fine-grained.
- Diorite is usually found in shades of gray and black, often speckled with lighter minerals.
Oceanic and Extrusive Textures
- Partial melting of the oceanic plate due to subduction causes basaltic magma formation, resulting in volcanic activity.
- The vesicular texture in some extrusive igneous rocks occurs due to trapped gas bubbles during rapid cooling.
- Coarse-grained rocks with visible minerals can be recognized visually without a microscope, characteristic of many intrusive rocks.
- Intrusive igneous rocks like granite and diorite exhibit a phaneritic texture, where individual crystals are easily identifiable.
- Obsidian displays a smooth texture and lacks visible grains due to rapid cooling that prevents crystal formation.
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Description
Learn about the formation of igneous rocks inside and outside the Earth's crust. Discover the difference between intrusive and extrusive igneous rocks and common examples like granite and diorite.
