Igneous Rocks
Igneous Rocks
* When magma or lava cools and freezes, it
becomes a mineral.
* A combination of minerals is a Rock.
*
Igneous
rocks are formed from the
crystallization of magma or lava.
-“
Ign
is,” the Greek word for “fire,” is like “Ignite,”
the English word for “to light”
How Are Igneous Rocks Classified?
How Are Igneous Rocks Classified?
1) By Texture
a) Extrusive
-cooled above ground (lava)
•
cooled quickly (a small amount of time)
•
small crystals (they cooled too quickly for
large crystals to grow)
•
may have a glassy texture (no crystals)
•
Fine Grained
How Are Igneous Rocks Classified?
1) By Texture
b) Intrusive
•
cooled inside the Earth (magma)
•
cooled off slowly (a big amount of time)
•
large crystals (they had time for big crystals to
grow)
•
Coarse grained
How Are Igneous Rocks Classified?
1) By texture
c) Porphyritic
•
has big and small crystals
•
slow cooling magma erupted and finished
cooling off quickly
How Are Igneous Rocks Classified?
2) By Mineral Composition
a) Felsic
•
Light color
•
Lightweight
•
High amount of silica
•
Examples: granite, rhyolite
How Are Igneous Rocks Classified?
2) By Mineral Composition
b) Intermediate
•
Medium color
•
Medium weight
•
Less silica
•
Examples: andesite, diorite
How Are Igneous Rocks Classified?
2) By Mineral Composition
c) Mafic
•
Dark color
•
Heavy
•
Low silica content
•
Rich in iron and magnesium
•
Examples: basalt, gabbro
How Are Igneous Rocks Classified?
2) By Mineral Composition
d) Ultramafic
•
Very dark color
•
Very heavy
•
Little silica
•
Rich in iron and magnesium
•
Form deep underground
•
Example: peridotite, kimberlite
Which
of
the
igneous
rocks
pictured
below
contains
the
greatest
amount
of
iron
and
magnesium?
Basalt
Granite
or
DARK
LIGHT
State
the
relative
crystal
size
(fine,
med.,
or
coarse
grained)
for
igneous
rocks
that
cooled
and
solidified
at
locations
A,
B,
and
C.
A.
B.
C.
A.
B.
C.
Coarse Grained
Fine Grained
Medium Grained
Where might a porphyritic texture form?
Mineral
Percentage
Plagioclase
Feldspar
58 %
Amphibole
31%
Biotite
11%
State
the
name
of
the
igneous
rock
that
has
a
coarse
grained
texture
and
the
following
mineral
composition:
Scrap
Paper
Scrap
Paper
58%
Scrap
Paper
58%
Igneous Rocks
Magma Classifications
1) Rhyolitic 70% Silica (SiO
2
)
2) Andesitic 60% SiO
2
3) Basalitic 50% SiO
2
Basalt is what makes up the ocean crust.
If only 50% is silica, there is room for
heavier elements in basaltic magma.