Igneous Flashcards
What is granite?
Granite is a phaneritic (coarse-grained) igneous rock with a felsic composition, typically composed of about 25% quartz and 65% feldspar, mainly Na-spar and K-spar. They can also contain minor amounts of muscovite and biotite micas, as well as amphibole (hornblende).
Rocks and magmas can also be described as granitic.
What does felsic mean?
Felsic is a term used to describe igneous rock or magma that are composed mainly of light colored silicates; primarily quartz, k-spar, and plagioclase, with minor amounts of amphibole and muscovite (light) mica.
Higher in silicon than other igneous rocks, they have highly connected structures and thus have less impurities (0% to 25% dark minerals), are lighter colored, and have relatively low melting points.
Felsic, from feldspar and silica (quartz).
What is rhyolite?
Rhyolite is the extrusive equivalent of granite.
It is an aphanitic (fine-grained) igneous rock with a felsic composition, typically composed of about 25% quartz and 65% feldspar, mainly Na-spar and K-spar. It is typically buff or pink colored, though it can also be light gray. It can frequently contain glass fragments or voids, and occasionally will contain amphibole (hornblende), and muscovite/biotite micas.
Rocks and magmas can also be described as rhyolitic.
What is andesite?
Andesite is a medium-gray aphanitic (fine grained) igneous rock containing roughly even amounts of felsic and mafic minerals, mainly amphibole and plagioclase, with smaller amounts of pyroxene and biotite (dark) mica.
Porphyritic textures are also very common, and will display light rectangular crystals of plagioclase feldspar or black elongated crystals of amphibole if phenocrysts are visible.
Andesitic rocks can often resemble rhyolite.
Andesite is named after the Andes Mountains in South America, though it’s also very common in the Cascades.
Rocks and magma can also be described as andesitic.
What does intermediate mean?
Intermediate composition is a term used to describe igneous rocks or magma that are have roughly even amounts of felsic and mafic minerals, and as such are moderately colored, have mid levels of silicon content, and are moderately well connected.
Intermediate rocks contain 25% to 45% dark silicate minerals, mainly amphibole (hornblende) and plagioclase, with lesser amounts of pyroxene, and biotite (dark) mica.
What does mafic mean?
Mafic is a term used to describe igneous rock or magma that contain 45% to 85% dark silicate minerals, mainly pyroxene and plagioclase feldspar, with lesser amounts of olivine and amphibole (hornblende).
Darker from their high iron and magnesium content, they are typically denser than lighter colored igneous rocks, and as such have a less connected structure, lower percentages of silicon, and a high melting point.
Mafic, from MAGnesium and Ferrum (iron).
What does ultramafic mean?
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What does phaneritic mean and what are common synonyms?
Igneous rocks with a phaneritic texture have slowly cooled and crystallized at great depths, with a coarse grained texture of intergrown crystals that are large enough to see without magnification.
Synonyms are coarse grained, intrusive, and plutonic.
Phaneritic, from phaner, meaning visible.
What does intrusive mean and what are common synonyms?
Intrusive igneous rocks have slowly cooled and crystallized at great depths, causing a coarse grained texture of intergrown crystals that are large enough to see without magnification.
Synonyms are phaneritic, coarse grained, and plutonic.
What does coarse-grained mean and what are common synonyms?
Igneous rocks with a coarse grained texture have slowly cooled and crystallized at great depths, causing intergrown crystals that are large enough to see without magnification.
Synonyms are phaneritic, intrusive, and plutonic.
What does fine-grained mean and what are common synonyms?
Igneous rocks with a fine-grained texture have quickly cooled and crystallized within the upper crust, creating a fine texture of intergrown crystals that are too small to distinguish individual minerals without magnification.
Synonyms are aphanitic and extrusive.
What does aphanitic mean and what are common synonyms?
Igneous rocks with an aphanitic texture have quickly cooled and crystallized within the upper crust, creating a fine grained texture of intergrown crystals that are too small to distinguish individual minerals without magnification.
Synonyms are fine grained and extrusive.
Aphanitic, from a, meaning not, and phaner, meaning visible.
What does extrusive mean and what are common synonyms?
Extrusive igneous rocks have quickly cooled and crystallized within the upper crust, creating a fine grained texture of intergrown crystals that are too small to distinguish individual minerals without magnification.
Synonyms are aphanitic and fine grained.
Aphanitic, from a, meaning not, and phaner, meaning visible.
What does pyroclastic mean and what is a common synonym?
Igneous rocks with a pyroclastic texture are a consolidation of individual rock fragments that are ejected during an eruption. They can be very fine ash, molten blobs, or angular blocks torn from the vent.
A common synonym is fragmental.
What does porphyritic mean?
Igneous rocks with a porphyritic texture contain some minerals that have slowly cooled and crystallized at great depths, causing a coarse grained texture, and then moved to a different environment (by eruption, for example) causing the remaining minerals to cool quickly, resulting in a fine grained texture as well.
The end result is a rock composed of large crystals embedded in a matrix of smaller crystals.
The term porphyritic precedes any other names when there are appreciable phenocrysts.
