GEO 303 Lecture Notes - Lecture 5: Gabbro, Oceanic Crust, Stratovolcano

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10 May 2016
Geo Lecture Chapter 5: Igneous Rocks
Next lecture: chapter 7
Lab: minerals, continued, ch 4
Next lab: chapter 6
?: Do we have to know chemical composition of silica?
Igneous Rocks:
oCharacteristics of igneous rock type
Cooling/Grain size/texture
Composition: felsic/mafic
Rocks: naturally occurring, solid aggregate, may be composed of
oMore than one mineral (ex: granite, basalt)
oOne mineral only (ex: limestone, marble)
oNo mineral (ex: coal, volcanic glass)
Classified by the way they form:
oIgneous rocks: crystalize from melts
oSedimentary rocks: form from sediments
oMetamorphic rocks: form by recrystallization of igneous or
sedimentary rocks
Igneous rocks: formed by cooling and solidification of magma or lava
oCooling at a temp where crystallization begins
oRocks can form at the surface (lava flowing at the surface, cools,
solidifies, forms minerals, called extrusive)
oOther types are ejected violently from the crater
oIntrusive rocks, formed in the subsurface, source of magma, molten
rock deep in the earth, cools, solidifies
Classified according to where they cool and solidified
oIntrusive (plutonic): magma cools beneath Earth’s surface
oExtrusive (volcanic): lava cools on earth’s surface
Intrusive: Igneous rocks, think of how they form by cooling rate
oDeep subsurface cools slower, going towards surface cools faster
cause less heat. Hitting surface is the fastest
oCooling slowly leads to big crystals
Size of crystals can tell what type they are
Extrusive igneous rocks: form by cooling of lava at the Earth’s surface
oCools quickly
oSmall or no crystals
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