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ROCK CYCLE
C
Unit 8
Rocks and Minerals
• Minerals are
elements or
compounds
• Rocks are MIXTURES
• Rocks are made of
different minerals
that are physically
combined together.
Rock-Forming
Minerals
•There are 4,000
known minerals
• Only 30 of them
make up rocks
Classifying Rocks
•Rocks are classified based on 3 criteria
• Formation (how they form)
• Color
• Provides clues on what minerals make up the rock
• Texture
• Look and feel of the rock’s surface
• Rocks are made up of small particles of different minerals,
called “grains”
• We look at grain size, shape, and patterns they make
Types of Rocks
•Three types of rocks
classified based on
how they are formed
• Igneous
• Metamorphic
• Sediment
Rock Cycle
• Contrary to what many
people believe, rocks can
change from one type to
another
• Rock Cycle = processes that
change one type of rock into
another type of rock
IGNEOUS ROCK
C
Formation
• Created when magma
or lava cools and
crystallizes in magma
chambers
• Different minerals
crystallize at different
temperatures
Formation (continued…)
• Steps to form an
igneous rock
1.
2.
3.
4.
Melting of rock
Turns to Magma
Magma cools
Crystallization
Formation (cont.)
• Extrusive rocks = igneous
rock that forms from lava
that erupted onto Earth’s
surface
• Intrusive rocks = rock that
formed when magma
hardened beneath the
Earth’s surface.
Texture
• The texture of the rocks can
tell us if the igneous rock is
extrusive or intrusive
• Small, hard to see rocks =
extrusive
• Lava cools very fast; large
crystals can’t form
• Large and interlocking rocks =
intrusive
• Magma cools more slowly;
large crystals can form
Composition
• The percentage of silicates (minerals
containing oxygen and silicon)
determine the characteristics of the
rock
• Felsic rocks
• High percentage of silicates
• Light colored
• Mafic rocks
• low percentage of silicates
• Dark colored
METAMORPHIC
ROCK
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Formation
• Form from the recrystallization of minerals inside existing
rocks
• Creates new minerals
• Formed through heat and pressure deep beneath the
Earth’s surface
Formation (continued)
•Steps to form metamorphic rock
1. Rocks are buried beneath the Earth’s surface
2. Heat “softens” minerals
3. Pressure causes minerals to recrystallize and rearrange
Texture
•Foliated
• Grains are rearranged
in parallel layers or
bands
•Non-foliated
• Mineral grains are
arranged randomly
SEDIMENTARY ROCK
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Formation
• Formed from rocks or minerals
that are broken down into smaller
pieces (sediment)
• Sediment comes from rocks or the
remains of living things (shells,
leaves, bones, etc) that are
broken down from erosion,
dissolving, or weathering
Formation (continued)
• Steps to forming sedimentary rock
1.
2.
3.
4.
5.
6.
Uplift (movement of rocks towards Earth’s surface)
Weathering/Erosion
Sedimentation (gravel, sand, silt, clay, etc)
Transport (wind/water carry sediments and sort them)
Deposition (sediments settles out of water or wind)
Lithification
• Cementation
• Compaction