Download Chp 5 Igneous Rocks.ppt

Warm Up
1. What is the purpose of the currents?
2. What are the 3 different types of
rocks?
3. How do you create each type of
rock?
https://www.youtube.com/watch?v
=aCnAF1Opt8M
Minerals
&
Rocks
IGNEOUS ROCKS
Igneous rocks
• Formed from the crystallization of magma or
lava
• Igneous rocks are classified two
ways
1.By the way they are formed
2.Their mineral composition and color
Lava is molten material on Earth’s
surface.
• Extrusive = form above Earth’s surface are
fine-grained and cool quickly
• Intrusive = form below Earth’s surface are
coarse-grained and cool slowly
Fine grained (extrusive)
Coarse grained (intrusive)
Igneous Rocks Mineral Classification
– Felsic light-colored igneous rocks and have high
silica contents.
– Mafic dark-colored igneous, have lower silica
contents, and are rich in iron and magnesium.
– Intermediate- are between Felsic and Mafic
– Ultramafic- Very low silica content and high
levels of iron and magnesium
The three main groups of igneous rocks are
felsic, mafic and intermediate. They are each
classified by their mineral compositions. An
example of a felsic rock is granite. An example
of a mafic rock is basalt. An example of a
intermediate rock is andesite.
• Ultramafic- Very low silica content and high
levels of iron and magnesium
Grain Size/Cooling Rates p. 109
When lava flows onto the Earth’s surface it is exposed to air and moisture.
Under these conditions, the lava cools quickly and there is not enough
time for crystals to form. Therefore, extrusive igneous rocks such as
obsidian have no visible mineral grains.
Cleavage- in structural geology and petrology, describes
a type of planar rock feature that develops as a result of
deformation and metamorphism
Texture
Mineral grains can have interlocking edges because
different cooling rates. Well-shaped crystals can form
during cooling. When this happens, porphyritic texture
occur.
• Rocks with a porphyritic texture can form when
crystals of two different sizes form together.
This could happen because of slow cooling
magma began cooling rapidly.
porphyritic
Igneous Rocks as Resources
• Igneous rocks have several characteristics that make
them especially useful as building materials.
– The interlocking grain textures of igneous
rocks help to give them strength.
– Many of the minerals found in igneous rocks
are resistant to weathering.
Ore Deposits
Ores are minerals that contain a useful
substance that can be mined for a profit.
Valuable ore deposits are often found
within igneous rocks.
–Ores are removed by underground
mining or from large, open-pit mines.
–If the cost of separating the waste
material becomes higher than the value
of the ore itself, then the mineral will no
longer be classified as an ore