Chapter 4
Rocks
Classifying Rocks
Section 1
Why must scientists who study rocks look at the
inside of them?
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Because the outside surfaces have been exposed to the
effects of ice, water, and weather (Erosion).
Mineral composition and color
2. What three important things do scientists observe when
studying rocks?
-Mineral composition, color, and texture
3. What are rock forming minerals?
-About 20 minerals that are found in the earth’s crust
that make up rocks.
4. What minerals are found in granite?
-Quartz, horneblende, mica, and feldspar
Mineral Composition:
(This is also in the igneous section
on page 2)
Most of Earth’s (rocks) contain Silica
Silica is a material formed from oxygen and silicon.
The silica content of magma and lava will affect the
types of rock that form
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High silica usually forms light colored rocks
Low silica usually forms dark colored rocks
5.Some other ways scientists study rocks include:
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Shape and color of the crystals
Mineral content
Color
Texture
And some other tests similar to the tests for minerals
Texture
Grains- Give the rock texture
What is texture?
Texture is the look and feel of the rocks surface.
The three grain sizes that make texture are:
1. Fine
2. Coarse
3. No visible
Texture: Grain Size
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Coarse grained = large grains and easy to see
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Fine grain = microscopic and too small to see
There are three main groups of rocks
Igneous – forms from cooling of magma or lava
Sedimentary – forms when particles of other rocks or the remains
of plants and animals are pressed and cemented together
Metamorphic – forms when and existing rock is changed by heat,
pressure or chemical reactions, forms deep underground
There are two grain shapes:
1.
2.
Jagged
Round
There are two grain patterns:
1. Banded
2. Non- banded
Igneous Rocks
Section 2
Igneous Rocks
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An igneous rock is any rock that forms from magma or
lava.
The name “igneous” comes from the Latin word meaning
“fire”
Igneous rocks come from deep within the ground
Igneous Rock Identification
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Igneous rocks are classified according to origin, texture
and mineral composition
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Origin
Texture
Mineral composition
Intrusive and Extrusive
Extrusive rock is formed from lava that erupted onto the
earth’s surface.
Intrusive rock is formed when magma hardens beneath the
surface.
Molten rock below the earth’s surface is called magma.
When it makes it to the surface it is called lava.
Igneous ID
Questions 5-7
Texture: depends on the size and shape of the mineral
crystals. The only exceptions are those rocks made of glass.
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Rapidly cooling lava forms fine-grained rock
Slowly cooling lava forms coarse-grained rocks with large
crystals
Intrusive rocks should have coarse-grained texture while
extrusive rock will have fine-grained texture.
Igneous Rocks Continued
Most of the earth’s rocks contain the mineral silica.
 Silica content of rocks can affect the rocks color.
Examples of Igneous rocks:
Rhyolite, Porphyry, Pegmatite, Granite, etc.
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Uses of Igneous Rock
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Building Material
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Cleaning and polishing
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granite
Pumice
Sharp tools for cutting or scraping
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obsidian
Sedimentary Rocks
Section 3
Sedimentary Rock
Sediment - small, solid pieces of material that come from
rock or living things.
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Ex. rock, shells, bones, leaves, stems, etc.
Sedimentary rocks are formed through the process of:
1.Erosion
2.Deposition
3.Compaction
4.Cementation
Rocks - Sedimentary Rocks
From Sediment to Rock
Most sedimentary rocks are formed through a series of
processes: erosion, deposition, compaction, and
cementation.
Sedimentary Rocks
*Erosion*
Erosion- destructive forces including heat, cold, rain, waves,
grinding ice, running water, wind and ice loosen and carry it
away.
(The forces of erosion form sediment)
Sedimentary Rocks
*Deposition*
Deposition - the process by which sediment settles out of the
water or wind carrying it
Sedimentary Rocks
*Compaction*
Compaction - the process that presses sediments together
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Thick layers build up over millions of years
The more layers, the more it presses down on the layers beneath
them.
Sedimentary Rocks
*Cementation*
Cementation - the process in which dissolved minerals
crystallize and glue particles of sediment together
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While compaction is occurring, the minerals slowly dissolve in the
water
Sedimentary Rocks
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3 major types of rocks
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Clastic
Organic
Chemical
Sedimentary Rock: Clastic
Clastic rock- a sedimentary rock that forms when rock
fragments are squeezed together
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Sediments can range in size
Ex. shale, sandstone, conglomerate, breccia
Sedimentary Rocks: Organic
Organic rock- forms where the remains of plants and animals
are deposited in thick layers
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Ex. coal, limestone
Sedimentary Rocks: Chemical
Chemical- when minerals that are dissolved in a solution
crystallize
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Ex. rock salt
http://www.youtube.com/watch?v=60jof35WuAo
http://www.brainpop.com/science/diversityoflife/coral/
Rocks From Reefs
Section 4
Rocks from Reefs
1.These rocks are made from the exoskeletons of coral animals.
2. Life can only live within the first 40 meters because that is
where there is enough light.
3. The exoskeletons are made from calcium.
4. A coral reef forms when the animals die and their skeletons
remain building up over time.
5. Temperatures must be warm.
6.Limestone deposits can tell us that there must have been on
ocean or sea there sometime in the past
Metamorphic Rocks
Section 5
http://www.brainpop.com/science/earthsystem/typesofro
cks/
Metamorphic Rocks
Heat and pressure beneath the surface of the earth can
change any rock into a metamorphic rock.
 Geologists classify metamorphic rocks according to the
arrangement of the grains that make up the rocks
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Foliated Rocks
Non-foliated Rocks
Metamorphic Rocks
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When a rock becomes a metamorphic rock…
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Its appearance changes
Texture changes
Crystal structure changes
Mineral content changes
Metamorphic Rocks
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Foliated = grains arranged in parallel layers or bands
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Ex. slate, schist and gneiss
Metamorphic Rock
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Non-foliated = mineral grains are arranged randomly
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Ex. marble, quartzite
Uses of Metamorphic Rocks
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Two of the most used metamorphic rocks
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Marble – building and sculptures
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Lincoln Memorial
Slate – flooring, roofing, walkways, chalkboards
The Rock Cycle
Section 6
The Rock Cycle
Forces deep within the Earth and at the surface, produce a
slow cycle that builds, destroys, and changes the rocks in the
crust.
The rock cycle is a series of processes that change rocks from
one kind to another.
Quartz
Sediment
Compaction
Cementation
Sedimentary Rock (sandstone)
Buried Pressure
Heat
Metamorphic Rock (quartzite)
What next?
ROCK CYCLE ACTIVITY