Download 22.3 Rocks and the Rock Cycle

21.3 Rocks and the Rock Cycle
 Rocks are classified into three major
groups based on how they formed
 Igneous Rocks
• Can be divided into two categories based on
where they form
A. Intrusive Rocks – igneous rocks that form
underground from magma
– Cool slowly allowing crystals to grow large
giving it a coarse-grain texture
B. Extrusive Rocks – igneous rocks that form at
the surface from lava
– Cool quickly resulting in the crystals to be small
giving it a fine grain texture
Igneous Rock Textures
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 II. Sedimentary Rock – rock that forms over time
as sediment is squeezed and cemented together
– Sediment – small, solid pieces of material that
comes from rocks or living organisms
• Sediment is deposited in layers by running water or
wind
• Sediment is cemented together by pressure from
overlying layers
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Three Main Groups of Sedimentary Rocks:
1. Clastic
2. Chemical
3. Organic
1. Clastic Rock – sedimentary rocks that
form from the broken fragments of other
rocks
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Clastic Rocks are classified based on the size
of their fragments
Example: Conglomerate – rock fragments
that consist of gravel and pebbles
 Some clastic rocks are made of smaller
particles (sandstone)
2. Chemical Rocks – rocks that form
when minerals precipitate out of solution
–
Example: when ocean water evaporates
(halite)
3. Organic Rocks– rocks that form as a
result of organic processes
Shells of marine animals like corals, clams,
mussels sink to the ocean floor when they
die.
– Example: Limestone and calcite (chalk)
 III. Metamorphic Rocks – rock that have
been changed by temperature, pressure, or
chemical reactions.
– Most metamorphic rocks form under high
temperatures and pressures deep underground.
(slate and schist– shown below)
Metamorphic Rocks
 Foliation: a layering of minerals in a rock
due to intense pressure squeezing the
crystals together.
Metamorphic Rock pictures
 Metamorphic Rocks like gneiss show
banding of light and dark minerals.
Metamorphic Rocks and their
Parent Rocks
 Examples:
– Slate: parent is shale
– Gneiss: parent is granite/schist
– Quartzite: parent is sandstone
– Marble: parent is limestone
IV. Rock Cycle
 Rock Cycle – series of processes in which rocks
continuously change from one type to another.