Classifying Igneous Rocks
Igneous rocks are formed either from magma cooling within the Earth, classified as intrusive or plutonic, or from lava cooling on Earth's surface, classified as extrusive or volcanic.
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Sebastien Seto Feldspar comes in different forms; plagioclase feldspar series Volcanic igneous rocks found
predominantly along west coast of NA
Plutonic igneous rocks found in Canadian Shield and along the west coast Fe and Mg content in Mafic make
Mafic darker than Felsic Igneous Rocks CHARACTERISTICS OF IGNEOUS ROCKS INTRUSIVE Appear green to black
Low Silica content Found in the Earth's mantle EXTRUSIVE Appear light grey
ex.Granite, Rhyolite Form in ocean basins and hot spots.
Apper dark grey
ex.Basalt Can be either Mafic, Intermediate, or Felsic TEXTURE OF ROCKS PORPHYRITIC Mix of smooth matrix and coarse crystals
from cooling slow to cooling fast PHANERITIC Coarse/Rough texture from slow cooling APHANITIC Smooth texture from fast cooling TWO TYPES OF IGNEOUS ROCK INTRUSIVE/PLUTONIC Forms from magma cooling and
crystallizing in the Earth EXTRUSIVE/VOLCANIC Forms from lava cooling and
crystallizing on Earth's surface EXAMPLES OF
IGNEOUS ROCK OBSIDIAN(similar to Rhyolite) RHYOLITE(2,3,8) ANDESITE(1,2,3,7) BASALT(3,7) GRANITE(3,4) MINERAL TYPES 8.QUARTZ 7.PYROXENE 6.ORTHOCLASE 5.OLIVINE 4.MUSCOVITE 3.FELDSPAR 2.BIOTITE 1.AMPHIBOLE TWO CLASSIFICATIONS OF MAGMA FELSIC "Acidic Magma" High in Silica content
Low Fe,Mg content MAFIC "Basic Magma" Low Silica content
High in Fe,Mg content THREE TYPES OF MAGMA RHYOLITIC Low temperatures:650-800 C
therefore high viscosity and gas content High in K,Na
Low in Fe,Mg,Ca 65-75% Silica content ANDESITIC Intermediate temperatures:800-1000 C
therefore medium viscosity and gas content Intermediate in chemical content 55-65% Silica content BASALTIC High temperatures:1000-1200 C
therefore low viscosity and gas content High in Fe,Mg,Ca
Low in K,Na 45-55% Silica(SiO2) content TYPES OF VOLCANIC
ERUPTIONS EFFUSIVE/
NON-EXPLOSIVE Characterized by very fluid (basaltic) lava EXPLOSIVE Spews a lot of smoke and tephra into the air Caused by viscous magma
