Transcript rocks-sec 2 igneous

Chapter 3 – Section 2
Igneous Rocks
Open your books to page 62 AND take
notes over the yellow slides!
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Igneous rock (from the Latin ignis meaning
born of fire)
Formation of Igneous Rocks
Igneous rocks are created when hot
magma OR lava cools and hardens
Rocks
Igneous Rocks – created
when hot magma or lava
cools and hardens
Magma – molten rock material located
underneath the Earth’s surface
Lava – magma that reaches Earth’s surface
– it comes out of volcanoes (see pg. 62,
figure 5)
Magma – below the
Earth’s surface
Lava – above the Earth’s
surface
Where does Magma come from?
In certain places within the Earth, the
temperature and pressure are just right for
rocks to melt and form magma.
Most magma comes from deep below the Earth’s surface
From near the surface to about 150 km
below the surface (this is 90 miles)
Temperatures from about 650 degrees C
(1,202 F)to 1200 degrees C (2,192 F)
Where does the heat come
from to cause rocks to melt?
The decay of radioactive
elements within Earth
Some heat was left over from when Earth
was formed, which originally was molten
Magma is less dense than the surrounding
rock and forced upward towards the
surface (volcano)
Intrusive vs. Extrusive
Igneous rocks are either intrusive or
extrusive, depending on how they were
formed.
Intrusive – igneous rocks that form
from magma below the Earth’s surface
(see pg. 63, figure 6)
- Takes a long time for these to cool, so they rock
crystals are larger and can be easily seen.
- Found at the Earth’s surface only after layers of
rock and soil have eroded away.
- Erosion takes place as these rocks are pushed up
towards the surface.
Intrusive – igneous rock forms
from magma below the Earth’s
surface. (They cool slowly so
crystals are large)
* Think IN – Inside the Earth
Extrusive – igneous rocks that form as
lava cools on the surface of the Earth
(see pg. 63, figure 6)
- When lava flows on Earth’s surface, it is
exposed to air and water
- Lava cools very quickly
- Quick cooling does not allow the atoms time to
arrange themselves so the crystals are very small.
Extrusive – igneous rocks that
form from lava on top of Earth’s
surface (they cool quickly so
crystals are small)
* Think EX – Exit the Earth
Volcanic Glass – cool very quickly so
few or no mineral grains are formed
Exp: obsidian, pumice, scoria
In pumice and scoria, gases become trapped in the
molten material as it cools. Some of these gases
escape and leave behind holes in the rock.
Volcanic Glass – cools very
quickly so few minerals grains
are formed Ex: obsidian,
pumice, scoria
Classifying Igneous Rocks
Igneous rocks are first classified by
whether they are intrusive or extrusive.
Then they are further classified by what
their magma is composed of
Basaltic Rock – dense, dark-colored rock.
Form from magma that is rich in iron and
magnesium (this gives the rock its dark
color)
Basaltic lava is fluid and flows freely from
volcano
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Basalt (an extrusive igneous rock in this
case); light colored tracks show the direction
of lava flow.
Basaltic Rock – dense, dark
colored rock. Made of iron (Fe) &
Magnesium (Mg)
(Iron gives the rock its dark color)
Granitic Rock – light colored rocks –
contains a lot of silica – magma is thick
and stiff
Because magma is stiff, it can build up
great pressure under Earth’s surface,
which is released violently during volcanic
explosions
Granitic Rock – light colored
rock (contains a lot of silica
magma)
- It’s stiff and thick
Andesitic Rock – have mineral
compositions between granitic and basaltic
These volcanoes can erupt violently
REVIEW TABLE 1 ON PG. 64
Andesitic Rock – has mineral
compositions of both granite &
basaltic rock
Here’s a short video about igneous rock