Earth’s Structure and Materials
Table of Contents
Igneous & Metamorphic Rocks
Ms. De Los Rios
7th Grade
Metamorphic Rock
Igneous Rock
Vocabulary 3.4
1. Extrusive Rock- Igneous rock that forms from lava on
Earth’s surface.
2. Intrusive Rock- Igneous rock that forms when magma
hardens beneath Earth’s surface.
3. Metamorphic rock a type of rock that forms when a
rock is changed by heat, pressure, or chemical
reactions.
4. Foliated- Term used to describe metamorphic rocks
that have grains arranged in parallel layers or bands.
Ignis means “fire” in Latin
Origin pg. 115
ALL igneous rocks form from magma or lava.
However, igneous rocks can look vastly different from each other.
What characteristics are used to classify igneous rocks?
Igneous rocks are classified by:
their origin, texture, and mineral composition.
• Igneous rock may form on or beneath Earth’s surface.
• Extrusive rock is igneous rock formed from lava that erupted onto
Earth’s surface.
• Basalt is the most common extrusive rock.
• Igneous rock that formed when magma hardened beneath the surface of
Earth is called intrusive rock.
• The most abundant intrusive rock in continental crust is granite.
How Do Geologist Classify Igneous Rocks? pg. 115
TEXTURE
The texture of an igneous rock depends on the size and shape of its mineral
crystals.
Rapidly Cooling Lava
Slowly Cooling
Magma
fine-grained igneous
rocks with small crystals
or no crystals at all
forms coarse-grained
rocks, such as granite,
with large crystals
Extrusive rocks have a
fine-grained or glassy
texture.
Intrusive rocks have
larger grains than
extrusive rocks.
Lava that is low in
silica=dark-colored
rocks=basalt.
Magma that is high in
silica=light-colored
rocks=granite.
Intrusive and extrusive rocks usually have different textures
Mineral Composition pg. 116
Magma and lava vary in silica
content.
What is Silica????
Silica is a material found in magma
that forms from oxygen and
silicon.
Lava that is low in silica=dark-colored
rocks=basalt.
Magma that is high in silica=lightcolored rocks=granite.
Uses of Igneous Rocks pg. 116
• People throughout history have
used igneous rock for tools and
building materials because they
are hard, dense, and durable.
• Granite has been used to build
statues, fortresses, bridges, and
public buildings.
• Today, thin polished sheets of
granite are used in curbstones
and floors.
•
Basalt is used for cobblestones
and as a material in landscaping
and roads.
How are Metamorphic Rocks Classified?
Pg. 116
Figure 2
Igneous rock has long been used as a
building material, such as for this Incan
fortress in Peru.
A fortress must be strong enough to
withstand violent attacks. Why might the
Incas have chosen igneous rock to build
their fortress near Ollantaytambu in
Peru?___________________________
________________________________
________________________________
________________________________
________________________________
Assess your Understanding
What Are Metamorphic Rocks? Pg. 117
Metamorphic rock can form out of igneous, sedimentary, or other met. rock.
Metamorphic rock= great heat, pressure=change in shape & composition
When great heat and pressure are applied to rock, the rock can change both
its shape and its composition
Any rock that forms from another rock as a result of changes in
heat or pressure (or both heat and pressure) is a metamorphic rock.
Many Met. Rocks are found in mts. or near large masses of igneous rocks.
WHY???
How Metamorphic Rocks Form? Pg. 114
Pockets of magma can rise through the crust. The high temperatures of these
pockets can change rock into metamorphic rock. Collisions between
Earth’s plates can also push rock down toward the heat of the mantle.
Plate collisions cause great pressure to be applied to rock while mountains
are being formed.
The pressure can deform,
change the physical shape of,
the rock. Under very high
temperature or pressure(or both)
the minerals in a rock can be
changed into other minerals.
The appearance, texture and crystal structure of the minerals in the rock
change.
How are Metamorphic Rocks Classified?
Geologists classify metamorphic rocks
according to the arrangement of the grains
making up the rocks.
Metamorphic rocks that have their grains
arranged either in parallel layers or bands
are said to be foliated.
Foliated describes the thin, flat layering found
in most metamorphic rocks.
Crystals in granite can be flattened to create
the foliated texture of gneiss.
Heat and pressure change the sedimentary rock
shale into slate.
As shale changes into slate, the mineral
composition of the shale can change.
Pg. 118
How Metamorphic Rocks Are Used
Some metamorphic rocks are nonfoliated.
The mineral grains in these rocks are
arranged randomly.
• Marble and quartzite are metamorphic
rocks that have a nonfoliated texture.
Quartzite forms out of quartz sandstone.
Marble usually forms when limestone is
subjected to heat and pressure deep
beneath the surface.
Figure 4 pg. 118
Great heat and pressure can change one Granite
type Of rock into another.
_______
Label each rock igneous or metamorphic _______
rock.
Indicate whether the metamorphic rock
is Foliated.
Then shade the correct arrow head to
show which rock can form from the
other rock.
Finally, alongside the arrowheads,
identify the subsurface
(underground) events that formed
The metamorphic rock.
_______
_______
Gneiss
_______
_______
How Metamorphic Rocks Are Used
pg. 119
• Marble and slate are very useful.
• They come in various colors.
• Because they are foliated (layers)
it splits easily into flat pieces.
• The metamorphic rocks marble
and slate are important materials
for building and sculpture.
Architects and sculptors use
marble for statues and buildings.
.
Terrace of Ca d’Zan
Sarasota Florida