Download 4/21/2012- Sedimentary Rocks, Metamorphic Rocks, and The Rock

Section
2
Section Check
What might you expect to find if you examined a rock
under a microscope?
A rock is a naturally formed mixture containing
minerals, rock fragments, or volcanic glass.
Underground igneous rocks form from molten rock
Magma
material called _______.
Extrusive igneous rocks form when _______
lava and ash
cools.
Section
2
Sedimentary Rocks,
Metamorphic Rocks, and
The Rock Cycle Notes
Chapter 26 Sections 3 & 4
Section
Sedimentary Rocks
3
Clasts
• Rock is a consolidated mixture of minerals. Some of
these minerals could be in bits and pieces of other
rocks. Such small rock and mineral fragments are
called clasts.
• Rocks inside Earth are protected from surface
conditions.
• Rock on Earth’s surface are exposed to water, wind,
and other forces.
Section
3
Sedimentary Rocks
Transportation and Deposition
• Mechanical weathering processes break down rocks into
smaller clasts.
• When clasts are transported to
new locations, they often become
rounded before being deposited.
• When clasts are loose on Earth’s
surface, they don’t fit together
perfectly. The empty space in
between the grains is called pore
space.
Section
3
Sedimentary Rocks
Compaction and Cementation
• When buried by more
sediment deposited above
them, clasts can be smashed
together with great force.
• The process by which clasts
stick together due to the
weight of overlying material is
called compaction.
Section
3
Sedimentary Rocks
Compaction and Cementation
• Water moving between clasts carries dissolved minerals
that can act as cement.
• Minerals precipitate slowly out of a water solution and
crystallize in the spaces between clasts in a process
called cementation.
• Most of the time both
compaction and cementation
work together to make
sedimentary rock.
Section
3
Sedimentary Rocks
Detrital Sedimentary Rock
• Detritus is another name given to clasts.
• Sedimentary rocks that are made mostly of clasts are
called detrital sedimentary rock.
• In order of decreasing size, clasts are known
as gravel, sand, silt, or clay.
Section
3
Sedimentary Rocks
Detrital Sedimentary Rock
• Geologists classify detrital sedimentary rocks based on
clast size.
• The size of the clast can
be used to infer how the
clast was transported.
• It takes more force, or
energy, to lift or move
gravel than it does to lift or
move sand.
Section
3
Sedimentary Rocks
Composition
• Detrital sedimentary rock
composition depends on
the types of weathered
rock material that is
transported, and
eventually deposited.
Section
3
Sedimentary Rocks
Detrital Sedimentary Rock
• Clast size also provides clues to
help determine the depositional
environment of the sediment that
formed the detrital rock.
Section
3
Sedimentary Rocks
Chemical Sedimentary Rocks
• Chemical sedimentary rocks form from water that
contains dissolved solids.
• If water receives more dissolved materials than it can
hold in solution, then the excess solid precipitates as
mineral crystals.
• Mineral crystals also precipitate out of a solution through
evaporation.
• This leaves an oversupply of dissolved matter and again
crystals.
Section
3
Sedimentary Rocks
Biochemical Sedimentary Rocks
• If sedimentary rocks contain the remains of living
organisms they are called biochemical sedimentary
rocks.
• Limestone is composed partly, of the remains of marine
organisms that had hard parts made of calcium
carbonate.
• Coal is a biochemical sedimentary rock composed
almost entirely of the carbon that remains after plant
material is compressed underground.
Section
4
Metamorphic Rocks and the Rock Cycle
Metamorphic Rocks
• Metamorphic rocks, have been changed by a
combination of heat, pressure, and chemical reactions.
• Any igneous, sedimentary, or metamorphic rock can
be changed by metamorphism.
Section
4
Metamorphic Rocks and the Rock Cycle
Textures
• Foliated rocks have crystals that are arranged in layers
and bands.
• Nonfoliated rocks have crystals with more random
orientations.
Section
4
Metamorphic Rocks and the Rock Cycle
Foliated Rocks
• Slate is a fine-grained foliated metamorphic rock that
splits easily along flat planes.
• Slate forms when
shale is
compressed
causing minerals,
like mica, to
oriente
perpendicular to
compression.
Section
4
Metamorphic Rocks and the Rock Cycle
Nonfoliated Rocks
• Nonfoliated metamorphic rocks tend to have random
crystal orientation and uniform grain size and uniform
color.
• Mineral grains tend to grow as the grade of
metamorphism increases.
Section
4
Metamorphic Rocks and the Rock Cycle
Metamorphic Rock Classification
• Mineral composition provides clues about the original
rock type before metamorphism, and indicates to what
degree a rock had been metamorphosed.
Section
4
Metamorphic Rocks and the Rock Cycle
The Rock Cycle
• The continual changing of rocks from one type to
another is called the rock cycle.
Section
4
Section Check
Question 1
Which is NOT an agent of metamorphism?
A. chemical reactions
B. pressure
C. heat
D. wind
Section
4
Section Check
Answer
The answer is D. Wind is responsible for erosion on some
rocks but it does not help form them.
Section
4
Section Check
Question 2
Describe foliated metamorphic rocks.
Section
4
Section Check
Answer
Foliated textures in metamorphic rocks exhibit
layering or mineral banding.
Section
4
Section Check
Question 3
Is there a beginning and end to the rock cycle?
Answer
No, the rock cycle is a continual process in which rocks
change from one form to another.
Section
4
End of Day
Homework: None