Classifying Igneous Rocks

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Igneous rocks

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Three main types of rocks

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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