Igneous Rock formed from Magma Crystals from molten rock > silica

1. Igneous Rocks
by Ann C. Cloutier Earth & Space Science
acloutier copyright 2011

2. Igneous rocks
are formed from the crystallization of magma.
 can form on or near the surface of Earth
>
extrusive igneous rock
 or form internally beneath the Earth surface >
intrusive igneous rock
 granite is the most common intrusive igneous
rock
 ignis is Latin for “fire”
 lava is magma that has flowed out onto Earth’s
surface
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3. Lava & Magma
are the same except where they cool
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Lava cools quickly on the
surface forming fine grained
crystals
> tuff, scoria, pumice
Ejected lava does not have
time to form crystals we can
see
> obsidian (volcanic glass)
rhyolite
Magma cools slowly beneath
Earth’s surface and forms
larger coarse grained igneous
rocks
> granite pegmatites
Aa and Pahoehoe are
Hawaiian words geologist use
for types of lava
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4. Magma is a mix of
gases, rock, water and mineral crystals

elements found in magma
are the same major elements
found in Earth’s crust

oxygen, silicon, aluminum,
iron, magnesium, calcium,
potassium , sodium
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Silica is the most abundant
and affects the characteristics
of magma
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5. Three types of magma
 Basaltic
Granitic
Andesitic
 magma characteristics vary due to water content
and silica Si O 2
water and silica can affect the melting
temperature
 which will affect the magma’s viscosity

(how it flows)
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6. How do rocks melt ?
 to melt rock we need temperatures ~ 800 * C –
1,200 * C
 partial melting occurs because different
minerals have different melting points
 magma can have a mix of molten rock and
unmelted rock crystals > which explains why
some crystal in magma are larger than others
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7. Pegmatite's are cooled magma
Gems often are found in pegmatites
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Gems are formed under
these conditions of slow
cooling magma deep
underground
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8. Geothermal Gradient
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affect the type of magma
formed
Temperature
Pressure
Water content
Mineral composition
The greater the pressure on the rock results in the
higher the melting point will become.
The greater the water content results in the decrease in
the melting point
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9. Where does all the heat come from ?
Heat is transferred from Earth’s core > to the mantle > on to the lithosphere
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10. Fractional Crystallization
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When magma cools, it crystallizes in the reverse order
of partial melting-the first minerals to crystallize from
magma, are the last minerals to melt during partial
melting
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11. Bowen’s Reaction Series
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Canadian geologist N.L.Bowen demonstrated that as
magma cools, minerals form in predictable patterns
known as Bowen’s Reaction Series (BRS) illustrates
the relationship between cooling magma and the
minerals that form
Two main patterns were discovered and documented
by Bowen:
1. a continuous pattern, with gradual changes of
mineral composition in the feldspar group
2. is characterized by an abrupt change of mineral types
in the iron-magnesium group discontinuous pattern
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12. Chart with Bowen’s Reaction
temperatures
http://
www.youtube.com/watch?v=en6ihAM9fe8
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magma type

13. Igneous Rock Formation
classified by light or dark minerals
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14. Classification of Igneous Rocks
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15. Silica content and Density
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16. Igneous Rocks
can be formed Intrusively or Extrusively
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Intrusive igneous rocks
form inside the Earth’s
crust
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Extrusively formed rocks
form outside or near the
surface of the Earth’s
crust
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17. Concept map of igneous rock formation
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18. Crystal size and cooling rate
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the relationship of how
large a crystal can
become is determined
by the amount of time
and space allowed for a
crystal to form.
small crystals cooled
quickly
larger crystals cooled
Rare and
s l o w l y
beautiful
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19. Felsic < > Mafic Rock
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Felsic rock such as granite, are light-colored and have
high silica content, contain quartz and the feldspars
orthoclase
Mafic rocks such as gabbro, are dark-colored have
lower silica content and are rich in iron and
magnesium
Mafic rocks can contain plagioclase, biotite,
amphibole, pyroxene and olivine
Grain size and texture give more clues when
identifying igneous rocks
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20. Texture of Igneous Rocks
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Porphyritic texture are rocks
with two different grain sizes
Granite is the most durable
igneous rock and is used in
many construction projects
Granite has interlocking
grain crystals which give it
great strength
Pegmatites have largegrained mineral crystals
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21. Kimberlite
There’s diamonds in them’
there hills or craters !
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22. Diamonds can be found on all
continents including the USA
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23. Ores
gold, silver, copper, lead
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valuable ore deposits are often associated with igneous
rocks
must be mined for a profit $$$$$
ores often form in the Earth when fluids left during
magma crystallization contain high levels of silica and
water.
leftover elements that were not incorporated into
common minerals
important metallic elements > gold,silver,lead,copper form
in metal rich veins
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24. Mining magnetite
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25. Most of New York’s skyscrapers
were built using granite > a strong igneous rock
I love the
Empire State
building !
The End
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