Transcript 3.2 Notes

 How
can two rocks made of the
same minerals look very different?
 Deep
inside Earth, temperatures
are hot enough (750 to 1250
degrees C) to melt rock.
 Molten
rock inside Earth is called
magma.
 Molten rock that reaches the surface
is called lava.
 An
igneous rock is classified
based on what minerals it has and
the size of its mineral crystals.
A
rock formed from magma
can have the same
minerals as a rock formed
from lava, but they will
have different crystal
structures and different
names.
 Intrusive
igneous
rock is formed when
magma cools inside
Earth.
› Example: Granite
(made of Quartz,
Feldspar, and Mica)
 Extrusive
igneous
rock is formed
when lava cools
on Earth’s surface.
› Example: Rhyolite
(made of Quartz,
Feldspar, and
Mica)
 Granite
and rhyolite have the
same mineral composition
(Quartz, Feldspar, Mica), but
were formed in different ways.
 The
texture of an igneous rock
refers to the size of its mineral
crystals.
 Large
crystals can form in
intrusive igneous rock
because:
 The
interior of the Earth
is very hot
 The high temperatures
allow magma to cool
slowly
 Slow cooling allows
time for large mineral
crystals to form
 Very
small crystals form in
extrusive rocks because…
 The
surface of the Earth
is cooler than inside
Earth.
 The lower temperatures
cause the lava to cool
quickly.
 There is no time for
large mineral crystals to
form.
To
identify igneous rocks,
you must consider both
their texture and their
mineral compositions.
 Most
igneous
rocks are made
up of silicate
minerals.
 Silicate
minerals
contain different
amounts of silica, a
mixture of silicon
and oxygen.
In
addition to
mineral composition and
crystal size, geologists also
sometimes classify igneous
rocks based on how much
silica they have in them.
 You
can estimate how much silica
is in an igneous rock by looking at
its color.
 Igneous
rocks with high levels
of silica are light in color.
› Examples: granite and rhyolite
 Igneous
rocks with low levels
of silica are dark in color.
› Examples: Gabbro and basalt
A
landform is a natural feature
on Earth’s land surface.
 Ship
Rock in New Mexico is an
example of the kinds of landforms
that are made of igneous rocks.
 As
magma pushes toward Earth’s
surface, it makes channels and
other formations underground.
 When
the rock above these
formations wears away, we have
intrusive rock formations on the
surface.
 When
magma makes its way
to Earth’s surface, the lava can
erupt in different ways.
 Lava
that is low in silica flows
easily and spreads out in thin
sheets.
 Lava
that is high in silica does not
flow easily, and usually results in
violent and explosive eruptions.
Geologists classify an igneous
rock on the basis of its crystal size
and the amount of ______ its
minerals contain.
A. Carbon
B. Silica
C. Sediment
D. Foliation
1.
2. What kind of texture would
obsidian (an igneous rock) have if it
cooled very quickly while it was
being formed?
A. Multicolored and banded
B. Smooth and shiny with no visible
grains
C. Coarse grains
D. Made up of jagged grains
3. What is the classification of a
rock formed inside Earth with
large, visible grains?
A. Intrusive igneous
B. Sedimentary
C. Metamorphic
D. Extrusive igneous