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
 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.
rock formed from magma
can have the same
minerals as a rock formed
from lava, but they will
have different crystal
structures and different
 Intrusive
rock is formed when
magma cools inside
› Example: Granite
(made of Quartz,
Feldspar, and Mica)
 Extrusive
rock is formed
when lava cools
on Earth’s surface.
› Example: Rhyolite
(made of Quartz,
Feldspar, and
 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
 Large
crystals can form in
intrusive igneous rock
 The
interior of the Earth
is very hot
 The high temperatures
allow magma to cool
 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
 The lower temperatures
cause the lava to cool
 There is no time for
large mineral crystals to
identify igneous rocks,
you must consider both
their texture and their
mineral compositions.
 Most
rocks are made
up of silicate
 Silicate
contain different
amounts of silica, a
mixture of silicon
and oxygen.
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
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
 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
 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
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
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