How are igneous rocks formed?
Igneous rocks are formed by the cooling and crystallization of molten rock.
Key Terms
How are igneous rocks formed?
Igneous rocks are formed by the cooling and crystallization of molten rock.
Intrusive and extrusive igneous rocks are classified based on what criteria?
How quickly the molten rock cools and crystallizes, and where this occurs with respect to Earth's surface
What is required to generate an igneous rock with a fine-grained texture?
A fine-grained texture is the product of rapid cooling and crystallization of lava.
A phaneritic texture is characteristic of a(n) __________ igneous rock that cooled __________.
intrusive; below the surface
What does it mean if an igneous rock has an aphanitic texture?
The igneous rock exhibits mineral crystals too small to see with the naked eye.
What three components make up most magmas?
Liquid Portion, Solid Portion, Gaseous Portion
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| Term | Definition |
|---|---|
How are igneous rocks formed? | Igneous rocks are formed by the cooling and crystallization of molten rock. |
Intrusive and extrusive igneous rocks are classified based on what criteria? | How quickly the molten rock cools and crystallizes, and where this occurs with respect to Earth's surface |
What is required to generate an igneous rock with a fine-grained texture? | A fine-grained texture is the product of rapid cooling and crystallization of lava. |
A phaneritic texture is characteristic of a(n) __________ igneous rock that cooled __________. | intrusive; below the surface |
What does it mean if an igneous rock has an aphanitic texture? | The igneous rock exhibits mineral crystals too small to see with the naked eye. |
What three components make up most magmas? | Liquid Portion, Solid Portion, Gaseous Portion |
name two minerals that are unlikely to coexist in the same igneous rock. | Muscovite and pyroxene |
Igneous rocks of felsic composition have __________ and __________ relative to mafic igneous rocks. | greater silica; lower melting temperature |
Which of the following is true about mafic igneous rocks? | Mafic igneous rocks are rich in Fe, Mg, and Ca. |
You have found a mafic rock with a phaneritic texture. What is a potential rock name? | Gabbro |
what minerals make up rhyolite? | Quartz, K-feldspar, and plagioclase feldspars, with relatively fewer biotite and amphiboles |
Which mineral class makes up most igneous rocks? | Silicates |
Peridotite is the main constituent of which part of the Earth? | Upper mantle |
Which two minerals define a felsic composition? | Quartz and Potassium Feldspar |
What is one way a glassy texture forms? | Lava cools rapidly. |
Which of the following describes a texture containing bubble-shaped cavities? | Vesicular |
Which of the following textures describes an igneous rock with anomalously large crystals? | Pegmatitic |
What does an igneous rock with a pyroclastic texture tell a geologist? | the rock was likely formed by a violent volcanic eruption. |
Which of the following textures indicates two stages of cooling and crystallization? | Porphyritic |
Which of the following igneous rocks contains no mineral crystals? | obsidian |
What is the term used to describe a very large, widespread, and deep intrusive body of igneous rock? | batholith |
In what type of igneous feature would you find rocks with a vesicular texture? | the surface of a lava flow |
Working in the field, you see a thin, dark-colored igneous sill across the valley. Without seeing the sill up close, what texture would you expect it to possess? | fine-grained |
Working in the field, you come upon a light-colored, fine-grained igneous rock that contains some very large dark-colored crystals. How do you account for this complex mineralogy? | The dark crystals formed first, undergoing slow cooling, and the remainder cooled quickly. |
Ultramafic rocks contain __________ and are commonly found in __________. | olivine; mantle |
What is an accessory mineral? | A mineral that makes up a relatively small portion of the total rock composition |
Which of the following best describes the difference between granite and rhyolite? | Granite is phaneritic and rhyolite is aphanitic. |
What is the rock name of an intermediate rock with two distinct grain sizes? | Andesite porphyry |
What do pumice and scoria have in common? | They both exhibit a vesicular texture. |
At a subduction zone, melting is triggered by _____. | the introduction of water |
Which is the following statements best describes the relationship between pressure and melting point in the Earth's Interior? | Higher melting points are determined by higher pressures |
What is the term used to describe increased temperature with depth in the Earth? | Geothermal gradient |
How can a magma body change its composition? CHOOSE ALL THAT APPLY. | Magmatic differentiation |
________ describes how an entire suite of silicate minerals can form from a single basaltic magma as it cools and crystallizes. | Bowen's Reaction Series |
Which mineral on the Bowen's Reaction Series will be the last to melt if an igneous rock is heated? | Olivine |
Which mineral on the Bowen's Reaction Series will be the first to melt if an igneous rock is heated? | Quartz |
Once a source rock partially melts, what does it produce? | Felsic magma and mafic residue |
According to Bowen's Reaction Series, __________ is one of the first minerals to melt, but last to crystallize. | quartz |
How is basaltic magma transformed into felsic magma? | Basaltic magma partially melts the continental crust, which is more felsic in composition. |
What causes an elevated geothermal gradient in a divergent plate setting? | Decompression melting of the mantle |
In a subduction zone, water driven from subducted oceanic crust causes __________. | the melting temperature of mantle rocks to decrease |
Which process is thought the generate most felsic magmas? | Heat from basaltic magma partially melting overlying crust |
What is the term for a tabular igneous pluton that occurs in an orientation that is discordant with the bedding surfaces of adjacent sedimentary rocks? | dike |
What is the term for a tabular igneous pluton that occurs in an orientation that is concordant with the bedding surfaces of adjacent sedimentary rocks? | sill |
Which of the following terms is best described as a massive pluton? | batholith |
Batholiths are known to form the cores of mountain ranges such as the Sierra Nevada. What is the implication of this observation? | Because batholiths form deep within Earth, the occurrence of one at the surface implies that it has since been uplifted and/or the rocks above have been removed. |
While working in the field, you find a dike cutting across some sedimentary rocks. What grain size would you expect to find in this pluton? | fine-grained |