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igneous rocks notes.notebook January 17, 2017
Origin• extrusive—volcanic; on the surface examples—rhyolite and basalt• intrusive—plutonic; beneath the surface examplegranite PullPull
Classification—igneous rocks are classified according to their texture and composition
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Texture—describes the size, shape, & arrangement of mineral crystals of which it is made. This depends on the rate at which the rock cooled.
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Composition—mineral composition of igneous rock PullPull
form from the cooling of magma or lava• crystallization: intergrown crystals formed when liquid rock cools PullPull
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PullIgneous Rocks
coarse grained (phaneritic)crystals are uniform and large enough to see w/o a microscope; magma cools slowlyExamples: gabbro, diorite,
and granite
fine grained (aphanitic)very small crystals; molten material cools quickly on or near the earth’s surface
Examples: Ryolite and basalt
Types of Igneous Textures
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igneous rocks notes.notebook January 17, 2017
porphyrtictwo very different contrasting sizes of crystals b/c of two different cooling rates that occurred for the rock
glassyno mineral crystals developed b/c of very rapid cooling; may also create a frothy appearance b/c of escaping gasses
Examples: obsidian and pumice.
Igneous Rock Composition
felsiclight colored, high silica; composed mainly of minerals quartz and potassium feldspar examplegranite
intermediatemixture of both light colored and dark colored minerals
maficdark colored minerals, low silica, but rich in iron and magnesium. examplebasalt
ultramaficcomposed of entirely dark minerals such as pyroxene or olivine; rarely observed on earth’s surface.
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