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Chapter 4
Rocks: Mineral Mixtures
Section 1: Understanding Rock
 The Earth’s crust is made up mostly of rock
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Rock – is simply a solid mixture of crystals of
one or more minerals
 Rocks come in all shapes and sizes
The Value of Rock
 Rock has been an important natural resource for as
long as humans have existed
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Early humans used rocks as hammers and to make
other tools
 Arrowheads and knifes were made out of rock
Rocks have also been used for centuries to make
buildings, roads, and monuments
Concrete is one of the most common building materials
today
 Rock is also very important to scientists
 What can be found by scientists in rock that give us
clues and evidence about past life on Earth?
The Rock Cycle
 The rocks in the Earth’s crust are constantly
changing
 The way that rock forms determines what type of rock
it is
 The three major types of rocks are;
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1) Igneous – is rock that forms from the cooling of
magma.
 Magma forms in the Earth’s lower crust and upper
mantle
2) Sedimentary – is rock that forms when sediments
are compacted and cemented together
 The sediments that form this rock come from
weathering and erosion
3) Metamorphic – is rock that forms when the texture
and composition of a preexisting rock is changed by
heat or pressure deep underground
(see page 83)
The Nitty-Gritty on Rock
Classification
 You now know that rocks are classified into three
main categories
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But these three main groups can be broken down into
smaller groups based on how and where the rock is
formed
 Scientists use composition and texture to further
classify rocks
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Composition – is the minerals that the rock are made
of
Texture – is determined by the size, shape, and grain
positions of the rock
 The texture of a rock is a good clue to how and where
the rock formed
Chapter 4 – Quiz 1
 1) ________ is simply a solid mixture of crystals of
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one or more minerals
2) ________ is rock that forms from the cooling of
magma.
3) ________ is rock that forms when sediments are
compacted and cemented together
4) ________ is the minerals that the rock are made of
5) ________ is determined by the size, shape, and
grain positions of the rock
Bonus - _________ is when magma cools beneath
the Earth’s surface
Answers
 1) Rock
 2) Igneous
 3) Sedimentary
 4) Composition
 5) Texture
 Bonus - Intrusive
Section 2: Igneous Rock
Origins of Igneous Rock
 The word igneous comes from the Latin word for
“fire”
 When magma or lava cools down enough it forms
igneous rock
 There are three ways that magma can form;
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1) Temperature
 Deep within the Earth temperatures are high enough
to melt rock
2) Pressure
 Hot rocks under extreme pressure will not melt until
the pressure is released
3) Composition
 When the composition of the rock changes
Igneous Rock Formations
 Intrusive – when magma cools beneath the
Earth’s surface
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Intrusive rock formations are name for their
size and the way they push into the
surrounding rock
 Extrusive – igneous rock that forms on the
Earth’s surface
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Most volcanic rock is extrusive
Section 3: Sedimentary Rock
 Through the process of erosion, sediment is
formed and transported from one place to
another
 As new layers of sediment are deposited they
eventually become compressed which
causes the sediments to become “glued”
together
 Sedimentary rock forms near or at the Earth’s
surface
 The most noticeable feature of sedimentary
rock is its layers – strata
Composition of Sedimentary Rock
 Classic Sedimentary Rock
 Sedimentary rock made of fragments of other
rocks and minerals
 Chemical Sedimentary Rock
 Sedimentary rock formed from solutions of
minerals and water
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This happens as rain water slowly makes its way
to the ocean
As it travels it dissolves some of the rock mineral
it passes through
Types include rock salt and limestone
Sedimentary Rock Structures
 Many sedimentary rock features can tell you
about the way the rock formed
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Stratification – how sedimentary rock is
layered
Section 4: Metamorphic Rock
 The word metamorphic comes from the meta,
meaning “changed” and morphos, meaning
“shape”
 Rock can undergo “metaporphism” by heat,
pressure, or a combination of both
Origins of Metamorphic Rock
 Most metamorphic
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