Download Reading Science!

6.10B: Classifying Rocks
Earth and Space
Reading Science!
Name: __________________________________________
Date: _____________
Classifying Rocks
Lexile 1060L
1
Have you ever picked up a rock that
you found interesting? Maybe as you
studied it you wondered where it
came from or how it was made. If you
look around, you will discover that
rocks are surrounding us. This is not
surprising considering that we live on
the crust of Earth which is made up
entirely of rock. Would you be
shocked to know that some of these
rocks have been around for billions of years while others aren’t
quite so old? New rocks are slowly formed all the time while old rocks are
slowly worn away by erosion. But no matter the age of the rock, they were
all formed in some way.
2
Rocks can be classified into three categories based on the way they were formed.
Volcanic action results in the formation of igneous rock. Deposition of Earth
material in layer upon layer results in the formation of sedimentary rock. Exposure
to extreme heat or pressure or both will cause some rocks to change from one
type to another. This changing results in the formation of metamorphic rock.
These formation processes result in characteristic appearances and properties that
provide the ability to classify rocks into one of the three categories.
1
R e a d i n g
S c i e n c e!
6.10B: Classifying Rocks
Earth and Space
3 Deep under the Earth’s crust the temperature is so high that it is hot
enough to melt rocks. This molten rock called magma will eventually cool
and harden forming rock within the crust. Occasionally, magma will find
its way through the crust through volcanic action. When this happens the
molten rock material is called lava rather than magma. As the lava flows it
also cools down and hardens. The types of rocks that are formed by
magma or lava that has cooled and hardened are known as igneous rocks.
Granite is an example of an igneous rock. Think of igneous rocks as rocks
that were formed by fire.
4 A second classification, sedimentary rocks, cover two thirds of Earth’s land
surface. Sedimentary rocks are made of bits and pieces of rocks that have
been eroded away, shells, and the remains of dead plants and animals. As
larger rocks are exposed to the elements on Earth such as rain, wind,
freezing, thawing, and plant roots growing, they are slowly worn away.
These bits of rock, now called sediment, are eventually carried by rivers to
the oceans and lakes. As the water slows down, the sediments settle to
the bottom layer by layer. Over millions of years all of the weight from the
upper layers along with sand and mud, turns the layer of sediments into
rock. Some sedimentary rocks appear to be banded, or layered because of
this. Also, many fossilized remains are found within the layers of
sedimentary rocks.
5 Metamorphic rocks are the third and final classification group.
Metamorphic rocks are the least common rock found on Earth. These
rocks, that were once an igneous, sedimentary or even a metamorphic
rock, have been changed by intense pressure and extreme heat from deep
inside the Earth. With enough heat and pressure the a rocks appearance,
structure and composition can result in the formation of a different rock.
Granite, that was once an igneous rock, will become gneiss when it is
placed under heat and pressure. Limestone, that was once a sedimentary
rock, will become marble as it is placed under heat and pressure. A
metamorphic rock can be thought of as a rock that changes.
2
R e a d i n g
6
S c i e n c e!
6.10B: Classifying Rocks
Earth and Space
The next time that you pick up a rock, think about how it could have been
formed. Was it formed by molten magma cooling and hardening, layers of
sediments pressing down on each other over time, or changed completely
by heat and pressure into a entirely different rock? On Earth there are only
these three types of rocks – igneous, sedimentary, and metamorphic.
3
Reading Science!
1
2
6.10B: Classifying Rocks
Earth and Space
3
As a volcano erupts it produces lava.
As this lava flows, it cools down and
hardens forming a rock. How could
you classify this rock?
A
As molten magma.
B
As a sedimentary rock.
C
As a metamorphic rock.
D
As an igneous rock.
Sometimes fossils can be found in
sedimentary rocks. Which statement
best explains why?
A
B
4
Heat and pressure from deep within
the Earth cause fossils to form.
The remains of dead plants and
animals settle to the bottom of an
ocean or lake and are covered by
mud. Pressure eventually forms
these layers into rock.
C
Lava may flow over an animal or
plant and as it cools and hardens a
fossilized rock is formed.
D
Larger rocks are slowly eroded
away by the elements on Earth.
4
A metamorphic rock can also be
thought of as a rock that changes.
What causes the rock to change?
A
Layers of sediment building up
over time and pressing down
forming rock.
B
Rain, wind, freezing, thawing, and
plant roots growing cause the rock
to erode away leaving behind
sediments.
C
Extreme heat and pressure from
deep within the Earth causes
changes to the rock’s appearance,
structure and composition.
D
The rock slowly changes over time
into a new rock.
How do scientist classify rocks?
A
By how they were formed.
B
By the minerals they are made of.
C
By their size and shape.
D
By where they were found.
Reading Science!
5
6.10B: Classifying Rocks
Earth and Space
What is similar about igneous rock
and metamorphic rock formation?
A
The formation of metamorphic
and igneous rock requires extreme
heat
B
!"#$%&'()*&+$&%$(#,)(&'-"./$)+0$
.1+#&23$'&/4$&//2'3$0##-$
2+0#'1'&2+0$
C
!"#$%&'()*&+$&%$(#,)(&'-"./$)+0$
.1+#&23$'&/4$'#325,3$.+$'&/43$,"),$
")6#$)$3.(.5)'$)--#)')+/#$
D
!"#$%&'()*&+$&%$(#,)(&'-"./$)+0$
.1+#&23$'&/4$'#72.'#3$5)8#'.+1$
5