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.