Contenu connexe Similaire à Rocks and weathering (20) Rocks and weathering4. Where do the rocks come from?
We get many useful substances from rocks, such as building
materials, metals, pigments and jewels. But where do we get
the rocks themselves from?
They come from the Earth’s crust. The Earth’s crust is the thin
outer layer of the Earth. It is about 30km thick on land and
only about 8km thick under the sea.
crust
mantle
inner core
outer core
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5. What is the Earth’s crust made of?
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6. Minerals and metals
Many of the useful substances we get from the Earth’s crust
are minerals, which contain metals.
Here are the names and formulae of some of the most
common minerals.
mineral formula metal extracted from it
Fe2O3
Al2O3
PbS
TiO2
CuFeS2
haematite
bauxite
galena
rutile
chalcopyrite
iron
aluminium
lead
titanium
copper
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7. Identifying rocks: summary
type examples description
sedimentary
metamorphic
igneous
sandstone
and
limestone
marble
and slate
basalt
and
granite
the softest rock
type, containing
layers and
sometimes fossils
usually harder than
sedimentary rocks,
containing thin layers
and twisted fossils
usually the hardest
rock type, containing
shiny crystals
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10. Pancake rocks in New Zealand
These limestone rocks at Punakaiki in New Zealand are
known as the Pancake Rocks. How do you think they were
formed?
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12. Properties of sedimentary rocks
What are the properties of sedimentary rocks?
Sedimentary rocks often
have layers showing the
deposition of sediment at
different time periods.
Sedimentary rocks are
made of lots of small
grains. These grains are
weakly held together so the
rocks are often porous and
may be soft and crumbly.
Sedimentary rocks often
have fossils trapped within
them.
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13. Rocks and weathering
Why are rocks all different shapes and sizes?
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14. What is weathering?
Rocks are different shapes and sizes because they are
changed by the conditions in their environment.
The breakdown of rocks into smaller fragments is called
weathering. Eventually the fragments become soil.
Can you think of anything that could cause weathering?
Rocks can be
weathered by
temperature change,
water, frost and even
plants and animals.
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15. Types of weathering
Which type of weathering
is caused by each of these:
temperature change
acid rain
plants and animals?
There are three types
of weathering:
physical weathering
biological weathering
chemical weathering.
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16. What is chemical weathering?
Slow chemical weathering
Rainwater is naturally a weak acid because carbon dioxide
in the air reacts with rainwater to form carbonic acid.
This weakly acidic rain reacts with minerals in rocks and
slowly wears them away.
Rapid chemical weathering
The burning of fossil fuels produces oxides of sulphur
and nitrogen, which make rainwater more acidic.
Acid rain reacts quickly with minerals, so the rocks get
weathered more rapidly.
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17. Examples of chemical weathering
How has chemical weathering affected these rocks?
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19. Acid and carbonate
When a carbonate
reacts with an acid, it
gives off carbon dioxide
gas.
How could you test the
gas given off, to
confirm that it is carbon
dioxide?
What would you
observe in this
test?
carbon dioxide
limewater
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20. Acid and carbonate
The products of the reaction between a carbonate and an
acid are a salt, carbon dioxide and water.
Calcium carbonate is a
substance that is naturally
found in the shells of sea
creatures and snails.
What salt do you think will be produced by the reaction
of hydrochloric acid and calcium carbonate?
calcium
carbonate
calcium
chloride
hydrochloric
acid
carbon
dioxide +
+ + water
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23. Erosion
As a rock is weathered, pieces of it fall off. This is called
erosion. They will then be transported away by water, wind
or glaciers.
by water by wind by glacier
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26. What is deposition?
Deposition occurs after
erosion and transportation.
This is the process that
occurs when pieces of
weathered rock sink to the
bottom of the river bed or
sea, forming sediment.
Eventually this sediment
gets so squashed down
that it forms new rock,
called sedimentary rock.
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27. Transportation by wind
Rock particles being transported by the wind cause erosion.
Wind erosion has two
major effects:
Small particles picked
up by the wind are
deposited in new places.
For example, this is how
sand dunes are formed.
When the particles are suspended in the air they can hit
objects and cause them to chip and wear down (think of
how sand grains sting when the wind blows them against
your skin at the beach.)
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28. Transportation by glacier
A glacier is a mass of ice that gradually moves overland.
As the glacier moves, the stones
and rocks in its path become
incorporated into the base. The
forward motion of the glacier
causes the trapped rocks to rotate,
scrape and grind along the ground.
This friction weathers the landscape
and causes valleys and fjords to form.
Over time the smaller pieces of rock
are carried into the melt water streams
that surround the glacier, where they
are redeposited on the ground.
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