Igneous rocks 2011acloutier copyright

acloutier copyright 2011acloutier copyright 2011

Igneous RocksIgneous Rocks by Ann C. Cloutier Earth & Space Science by Ann C. Cloutier Earth & Space Science


Igneous rocksIgneous rocks are formed from the crystallization of magma.are formed from the crystallization of magma.

can form can form on or near theon or near the surface of surface of Earth > extrusive igneous rockEarth > extrusive igneous rock

or form internally or form internally beneathbeneath the Earth the Earth surface > intrusive igneous rocksurface > intrusive igneous rock

granite is the most common intrusive granite is the most common intrusive igneous rockigneous rock

ignis is Latin for “fire”ignis is Latin for “fire” lava is magma that has flowed out lava is magma that has flowed out

onto Earth’s surfaceonto Earth’s surface


Lava Lava && MagmaMagmaare the same except where they coolare the same except where they cool

Lava cools quickly on Lava cools quickly on the surface forming the surface forming fine grained crystals fine grained crystals

> tuff, scoria, pumice> tuff, scoria, pumice Ejected lava does not Ejected lava does not

have time to form have time to form crystals we can see crystals we can see

> obsidian > obsidian (volcanic glass)(volcanic glass) rhyoliterhyolite

Magma cools slowly Magma cools slowly beneath Earth’s surface beneath Earth’s surface and forms larger coarse and forms larger coarse grained igneous rocks grained igneous rocks

> granite pegmatites> granite pegmatites Aa and Pahoehoe are Hawaiian words

geologist use for types of lava


Magma is a mix of Magma is a mix of gases, rock, water and mineral gases, rock, water and mineral

crystalscrystals elements found in elements found in

magma are the same magma are the same major elements found in major elements found in Earth’s crustEarth’s crust

oxygen, silicon, oxygen, silicon, aluminum, iron, aluminum, iron, magnesium, calcium, magnesium, calcium, potassium , sodiumpotassium , sodium

Silica is the most Silica is the most abundant and affects the abundant and affects the characteristics of magmacharacteristics of magma


Three types of magmaThree types of magma

Basaltic Granitic Basaltic Granitic AndesiticAndesitic

magma characteristics vary due to magma characteristics vary due to water content and silica Si O water content and silica Si O 2 2

water and silica can affect the water and silica can affect the melting temperature melting temperature

which will affect the magma’s which will affect the magma’s viscosity viscosity (how it flows)(how it flows)


How do rocks melt ?How do rocks melt ?

to melt rock we need temperatures ~ to melt rock we need temperatures ~ 800 * C – 1,200 * C800 * C – 1,200 * C

partial melting occurs because partial melting occurs because different minerals have different different minerals have different melting pointsmelting points

magma can have a mix of molten magma can have a mix of molten rock and unmelted rock crystals > rock and unmelted rock crystals > which explains why some crystal in which explains why some crystal in magma are larger than othersmagma are larger than others


Pegmatite's are cooled Pegmatite's are cooled magmamagma

Gems often are found in Gems often are found in pegmatitespegmatites Gems are formed Gems are formed

under these under these conditions of slow conditions of slow cooling magma cooling magma deep undergrounddeep underground


Geothermal Gradient Geothermal Gradient

affect the type of magma affect the type of magma formed formed

TemperatureTemperature PressurePressure Water contentWater content Mineral compositionMineral composition

The greater the pressure on the rock results The greater the pressure on the rock results in the higher the melting point will become.in the higher the melting point will become.The greater the water content results in the The greater the water content results in the decrease in the melting pointdecrease in the melting point


Where does all the heat come Where does all the heat come from ?from ?

Heat is transferred from Earth’s core > to the mantle > on to Heat is transferred from Earth’s core > to the mantle > on to the lithospherethe lithosphere


Fractional CrystallizationFractional Crystallization

When magma cools, it crystallizes in the When magma cools, it crystallizes in the reverse order of partial melting-the first reverse order of partial melting-the first minerals to crystallize from magma, are minerals to crystallize from magma, are the last minerals to melt during partial the last minerals to melt during partial meltingmelting


Bowen’s Reaction SeriesBowen’s Reaction Series Canadian geologist N.L.Bowen demonstrated Canadian geologist N.L.Bowen demonstrated

that as magma cools, minerals form in that as magma cools, minerals form in predictable patternspredictable patterns

known as Bowen’s Reaction Series (BRS) known as Bowen’s Reaction Series (BRS) illustrates the relationship between cooling illustrates the relationship between cooling magma and the minerals that formmagma and the minerals that form

Two main patterns were discovered and Two main patterns were discovered and documented by Bowen:documented by Bowen:

1. a 1. a continuous patterncontinuous pattern, with gradual changes of , with gradual changes of mineral composition in the feldspar groupmineral composition in the feldspar group2. is characterized by an abrupt change of mineral 2. is characterized by an abrupt change of mineral

types types in the iron-magnesium group in the iron-magnesium group discontinuous discontinuous patternpattern


Chart with Bowen’s ReactionChart with Bowen’s Reactiontemperaturestemperatures

magma typemagma type

http://http://

www.youtube.com/watch?v=en6ihAM9fe8www.youtube.com/watch?v=en6ihAM9fe8


Igneous Rock FormationIgneous Rock Formationclassified by light or dark mineralsclassified by light or dark minerals


Classification of Igneous Classification of Igneous RocksRocks


Silica content and DensitySilica content and Density


Igneous Rocks Igneous Rocks can be formed Intrusively or can be formed Intrusively or

ExtrusivelyExtrusively Intrusive igneous Intrusive igneous

rocks form inside rocks form inside the Earth’s crustthe Earth’s crust

Extrusively formed Extrusively formed rocks form outside rocks form outside or near the surface or near the surface of the Earth’s crustof the Earth’s crust


Concept map of igneous rock Concept map of igneous rock formationformation


Crystal size and cooling rateCrystal size and cooling rate the relationship of the relationship of

how large a crystal how large a crystal can become is can become is determined by the determined by the amount of time and amount of time and space allowed for a space allowed for a crystal to form.crystal to form.

small crystals cooled small crystals cooled quicklyquickly

larger crystals cooled larger crystals cooled

s l o w l ys l o w l yRare and beautiful


Felsic < > Mafic RockFelsic < > Mafic Rock

Felsic rock such as granite, are light-Felsic rock such as granite, are light-colored and have high silica content, colored and have high silica content, contain quartz and the feldspars contain quartz and the feldspars orthoclaseorthoclase

Mafic rocks such as gabbro, are dark-Mafic rocks such as gabbro, are dark-colored have lower silica content and are colored have lower silica content and are rich in iron and magnesiumrich in iron and magnesium

Mafic rocks can contain plagioclase, Mafic rocks can contain plagioclase, biotite, amphibole, pyroxene and olivinebiotite, amphibole, pyroxene and olivine

Grain size and texture give more clues Grain size and texture give more clues when identifying igneous rockswhen identifying igneous rocks


Texture of Igneous RocksTexture of Igneous Rocks Porphyritic texture are Porphyritic texture are

rocks with two different rocks with two different grain sizesgrain sizes

Granite is the most Granite is the most durable igneous rock durable igneous rock and is used in many and is used in many construction projectsconstruction projects

Granite has interlocking Granite has interlocking grain crystals which grain crystals which give it great strengthgive it great strength

Pegmatites have large-Pegmatites have large-grained mineral crystalsgrained mineral crystals


Kimberlite Kimberlite There’s diamonds in them’ there hills or craters !

Diamonds can be found on Diamonds can be found on all continents including the all continents including the

USA USA



OresOresgold, silver, copper, leadgold, silver, copper, lead

valuable ore deposits are often associated valuable ore deposits are often associated with igneous rockswith igneous rocks

must be mined for a profit $$$$$must be mined for a profit $$$$$ ores often form in the Earth when fluids ores often form in the Earth when fluids

left during magma crystallization contain left during magma crystallization contain high levels of silica and water. high levels of silica and water.

leftover elements that were not leftover elements that were not incorporated into common mineralsincorporated into common minerals

important metallic elements important metallic elements > > gold,silver,lead,copper form in metal rich veinsgold,silver,lead,copper form in metal rich veins

Mining magnetiteMining magnetite



Most of New York’s skyscrapers Most of New York’s skyscrapers were built using granite > a strong were built using granite > a strong

igneous rockigneous rock

The EndThe End

I love the Empire State

building !

Igneous rocks 2011acloutier copyright

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