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Igneous Rocks - New Roads School

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					Igneous Rocks
      Types Of Igneous Rocks
Types Of Igneous Rock
    Igneous rocks are mainly classified on basis of their texture an composition.

Main Types
Granite,A coarse-grained igneous rock composed of K-feldspar, plagioclase, and quartz,
    with small amounts of mafic minerals

Diorite,A phaneritic intrusive igneous rock consisting mostly of intermediate plagioclase
    feldspar and pyroxene, with some amphibole and biotite.

gabbro, A dark-colored, coarse-grained rock composed of Ca-plagioclase, pyroxene, and
   possible olivine, but no quartz.

rhyolite, A fine-grained volcanic rock composed of quartz, K-feldspar, and plagioclase. It is
    the extrusive equivalent of a granite.

andesite, Afine-grained igneous rock composed mostly of plagioclase feldspare and fom 25
   to 45% pyroxene, amphibole, or biotite, but no quartz or K-feldspar. It is abundant in
   mountains bordering the Pacific Ocean, such as the Andes Mountains of South
   America, from which this name was derived.

Basalt, A dark-colored, fine-grained, mafic volcanic rock composed of plagioclase (over
   50%) and pyroxene. Olivine may or may not be present.
Textures
Rocks with Phaneritic Textures
Granite
Dirorite
Gabbro
Peridotite
Rocks with Aphanitic Textures
Rhyolite
Andesite
Basalt
Komatiite
     Rocks with Pyroclasti Textures

Ash-Explosive volcanic eruptions of rhyolitic and
  andesitic magmas commonly produce large
  volumes of fragmental material that are ejected
  high into the atmosphere, the fragments range
  from dust-size pieces a.k.a ash.
Pumice- is a vescular frothy glass common among
  the larger fragments.
Tephra- deposits are composed of shrads of volcanic
  glass, pumice, broken phenocrysts, and foreign
  rock fragments.
The other rock textures are, tuff, pyroclastic-fall tuff,
  and ash-flow tuff.
Extrusive Rock Bodies
 Extrusive igneous
 rocks form from
 magma that
 extrudes onto the
 earth’s surface
 from volcanic
 eruptions, these
 rocks include lava
 flow and volcanic
 ash.
Products of Basaltic Eruptions
 Basaltic eruptions are probably the most
 common type of volcanic activity on Earth.
 The lava is generally extruded from
 fractures or fissures in the crust. Basaltic
 lavas erupt with temperatures ranging
 between 1000 and 12000 C.THE lava can
 flow with speeds up to 40 km/hr down
 steep slopes, but rates of 20 km/hr are
 considered unusually rapid. EX, the
 basaltic lava on Galapagos islands move
 an average of 170 m/hr.

				
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posted:12/3/2011
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