Transcript Rocks and the Rock Cycle - martin

Rocks and the Rock Cycle
Ch 10.2
Please take notes
Rocks
• Rocks are made of
minerals
– Minerals are
inorganic, naturally
occurring solid
materials (pure or
compound)
– Can you think of any
examples of
minerals?
Rock Families
• There are three families
– Igneous
– Sedimentary
– Metamorphic
The word igneous comes from the Latin word
ignis- meaning fire… why call them igneous?
Igneous Rock
• Formed when hot
magma and hot lava
cool and solidify
• 2 types are:
– Intrusive: when magma
cools and solidifies in the
Earth’s crust (granite)
– Extrusive: when lava
cools and solidifies on the
Earth’s crust
See fig 10.11, page 289
Also: Rock Hounds - Igneous
Rock
Sedimentary Rock
• Is made up of sediments, loose
material (rock, minerals, plants
and animal remains). They
become closely packed and
cemented together
• Form layers called beds
• Formed by compaction
Limestone is sedimentary rock made up of
fossils, organic sedimentary rock
See Fig 10.14ABC, page 293
Also:
Rock Hounds - Sedimentary Rock
Metamorphic Rock
• Is a rock that has changed
from the parent rock
(original rock) due to
intense pressure or heat.
Slate
Schist
(from shale)
See fig 10.16, page 294
Also:
Rock Hounds - Metamorphic Rock
Gneiss
The Rock
Cycle
• Rocks continue to change
in an ongoing process
called the Rock Cycle
–
See fig 10.17, page 295
Weathering
• Weathering is the natural break down of
rocks
Three Types Are:
• Mechanical
• Chemical
• Biological
Mechanical Weathering
• Abrasion
– Abrasion is the wearing down of rocks by solid
particles carried by wind or water.
• Frost
– Freezing water can cause a lot of damage to rocks.
This happens because when water freezes it
expands, or spreads out and gets larger. When water
gets into cracks in rocks and freezes, it also
expands. This expansion of water when it freezes
can produce enough force to crack rocks apart.
•
Gravity
– Gravity is another cause of erosion because it can
pull loose materials down hills in a landslide.
Abrasion
– Rocks found in rivers are
usually very smooth and
round. The moving water
carries with it loose rocks
and other materials. These
pieces crash into one
another and are sometimes
scraped along the river bed
which can break the rocks
into smaller pieces.
– The wind can also pick up
sand and slam them into
other rocks. The sharp
edges of the sand can have
a dramatic effect on larger
rocks and sometimes
creates very stunning
formations.
Frost/Wedging
•
If you've ever placed a closed
container such as a soda pop
in the freezer and forgot about
it you probably returned to find
that the container had been
split open.
•
Potholes in roads and cracks in
rocks are often caused by the
repeated freezing and
expansion of water in small
cracks.
•
Road crews are busiest during
early spring trying to repair the
potholes caused by the cold
temperatures of winter.
Gravity
• A landslide is a large, sudden
movement of loose rocks and
soil.
• As the rocks are falling down the
hill they bump into one another
and can be broken into smaller
pieces.
• The rocks on a hill can be
loosened by other factors such as
heavy rains or human activity.
Chemical Weathering
• Chemical reactions break down
the bonds holding the rocks
together, causing them to fall
apart, forming smaller and
smaller pieces.
• Chemical weathering is much
more common in locations
where there is a lot of water.
This is because water is
important to many of the
chemical reactions that can
take place. Warmer
temperatures are also more
friendly to chemical weathering.
Types of Chemical Weathering
• Oxidation takes place when oxygen combines with
other elements in rocks to form new types of rock. These
new substances are usually much softer, and thus easier
for other forces to break apart.
• Hydrolysis occurs when water combines with the
substances in rocks to form new types of substances,
which are softer than the original rock types. These
allows other forces such as mechanical weathering to
more easily break them apart.
• Carbonation takes place when carbon dioxide reacts
with certain types of rocks forming a solution, that can
easily be carried away by water.
Biological Weathering
• The word ‘bio’
means life. Thus
biotic or biological
weathering is any
type of weathering
that is caused by
living organisms.
Types of Biological Weathering
• Most often the culprit of biotic weathering are plant roots.
These roots can extend downward, deep into rock
cracks in search of water, and nutrients. In the process
they act as a wedge, widening and extending the cracks.
• Other causes of biotic weathering are digging animals,
microscopic plants and animals, algae and fungi.