Igneous Rocks and Their Formation

Questions and Answers

What is the difference between magma and lava?

Magma is molten rock inside the Earth while lava is magma that reaches the surface.

What do the terms extrusive and intrusive refer to?

Extrusive - quick cooling at surface (correct)

Intrusive - quick cooling at surface

Extrusive - slow cooling at depth

Intrusive - quick cooling at surface

What is the difference between volcanic and plutonic igneous rocks?

Volcanic rocks are extrusive and formed at the surface, while plutonic rocks are intrusive and formed in the crust.

What determines the difference between volcanic and plutonic rocks?

The location of formation; volcanic rocks form at the surface, while plutonic rocks form at depth. Signup and view all the answers

What is the difference between basalt and gabbro?

Basalt is volcanic (extrusive) and gabbro is plutonic (intrusive). Signup and view all the answers

What is the difference between andesite and diorite?

Andesite is volcanic (extrusive) and diorite is plutonic (intrusive). Signup and view all the answers

What is the difference between granite and rhyolite?

Granite is plutonic (intrusive) and rhyolite is volcanic (extrusive). Signup and view all the answers

What is the difference between obsidian and pumice?

Obsidian forms from regular magma, while pumice forms from cooling gassy, frothy magma. Signup and view all the answers

What is the difference between mafic and felsic rocks?

Mafic rocks are darker and denser, composed of iron and magnesium, while felsic rocks are lighter and high in silicate. Signup and view all the answers

What rocks are considered mafic, felsic, or intermediate?

Basalts and gabbros are mafic; obsidian and pumice are felsic; andesites and diorites are intermediate. Signup and view all the answers

What is the difference between granite and granodiorite?

Granite has less magnesium and iron, while granodiorite contains more dark minerals. Signup and view all the answers

Which igneous rock type best represents the Sierra Nevadas?

Granitic rocks of the Mesozoic age. Signup and view all the answers

What major compositional layer of the Earth do ultramafic rocks containing olivine or serpentine represent?

Oceanic crust. Signup and view all the answers

What are the characteristic rocks of convergent plate boundaries?

Granites, rhyolites, andesites, and diorites. Signup and view all the answers

What is a pluton?

A pluton is a plutonic rock formed intrusively. Signup and view all the answers

What is a batholith?

A giant plutonic intrusion. Signup and view all the answers

Where can you find ancient and young basaltic rocks in California?

Mesozoic era basaltic rocks can be found in Mt. Shasta, Lassen, and Cascade volcanoes, while young basaltic rocks are in the Mojave and Basin range of eastern California. Signup and view all the answers

Where can you find Mesozoic felsic rocks in California?

In the Sierra Nevadas. Signup and view all the answers

Where can you find Quaternary rocks in California?

In the Coast Ranges and the Mojave and Basin ranges of eastern California, as well as at the Cascade andesitic volcanoes in the north. Signup and view all the answers

Study Notes

Magma and Lava

Magma is molten rock located beneath the Earth's surface; when it reaches the surface, it becomes lava.
Extrusive igneous rocks form from rapidly cooled lava, while intrusive igneous rocks crystallize from slowly cooled magma deep underground.

Volcanic vs. Plutonic Igneous Rocks

Volcanic rocks (extrusive) solidify at the Earth’s surface; examples include basalt and rhyolite.
Plutonic rocks (intrusive) solidify beneath the surface; examples include gabbro and granite.
Texture differences: intrusive rocks tend to be coarse-grained, while extrusive are usually fine-grained or glassy.

Types of Igneous Rocks

Basalt is a volcanic mafic rock; gabbro is its plutonic counterpart.
Andesite (volcanic) and diorite (plutonic) are intermediate rocks found at convergent boundaries.
Granite (plutonic) is felsic, while rhyolite (volcanic) is its extrusive equivalent.

Obsidian vs. Pumice

Both obsidian and pumice are volcanic rocks; obsidian is dense and glassy, while pumice is formed from gas-rich lava, giving it a frothy texture.

Mafic and Felsic Rocks

Mafic rocks are rich in iron and magnesium, darker, denser, and typically contain little to no water; examples include basalt and gabbro.
Felsic rocks are high in silica, lighter, less dense, and contain water in their mineral compositions; examples include quartz-rich rocks like granite.

Granite vs. Granodiorite

Granite contains less magnesium and iron, leading to a higher quartz content.
Granodiorite contains more calcium and sodium, resulting in the presence of more dark minerals.

Regional Igneous Rock Abundance

Sierra Nevadas are primarily composed of granitic rocks from the Mesozoic era.
The Cascades volcanic chain mostly features andesitic rock.

Ultramafic Rocks

Ultramafic rocks, such as those containing olivine or serpentine, are indicative of the oceanic crust.

Igneous Rock at Plate Boundaries

Convergent boundaries typically show granites, rhyolites, andesites, and diorites.
Divergent boundaries generally have basalt and gabbro.
Transform faults feature a variety of igneous rock types.

Plutons and Batholiths

A pluton is a body of intrusive igneous rock; a batholith is a large plutonic intrusion.
The Sierra Nevada contains a prominent batholith made up of granitic rocks.

Basaltic Rocks in California

Mesozoic basaltic rocks are found in regions like Mount Shasta, Lassen, and the Cascade volcanoes.
Young basaltic rocks from the Late Cenozoic are located in the Mojave and the eastern Basin Range.

Felsic Rocks in California

Mesozoic felsic rocks are primarily found in the Sierra Nevadas.
Quaternary rocks are located in the Coast Ranges, Mojave, eastern California Basin Ranges, and the northern Cascade andesitic volcanoes.

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Explore the fascinating world of igneous rocks, including the differences between volcanic and plutonic types. This quiz covers magma and lava, types of igneous rocks, and their textures. Test your knowledge on basalt, granite, obsidian, and more!