Rocks and weathering

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Useful substances from rocks

What useful substances do we get from rocks?


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


What is the Earth’s crust made of?


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.

Fe2O3

Al2O3

PbS

TiO2

CuFeS2

haematite

bauxite

galena

chalcopyrite

rutile

mineral formula metal extracted from it

iron

aluminium

lead

titanium

copper


Identifying rocks: summary

sedimentary

metamorphic

igneous

sandstone

and

limestone

marble

and slate

basalt

and

granite

the softest rock

type, containing

layers and

sometimes fossilsusually harder than

sedimentary rocks,

containing thin layers

and twisted fossils

usually the hardest

rock type, containing

shiny crystals

type examples description


Different rocks = different uses


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?


What are sedimentary rocks?

sandstone

limestone chalk


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.


Rocks and weathering

Why are rocks all different shapes and sizes?


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.


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.


What is chemical weathering?

Slow chemical weathering

Rapid 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.

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.


Examples of chemical weathering

How has chemical weathering affected these rocks?


Which type of weathering?


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


Acid and carbonate

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

acidwater+ +

carbon

dioxide+

The products of the reaction between a carbonate and an

acid are a salt, carbon dioxide and water.


Reaction of carbonates


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


Transportation by water


Rock changes during transportation


What is deposition?

Deposition occurs after

erosion and transportation.

Eventually this sediment

gets so squashed down

that it forms new rock,

called sedimentary rock.

This is the process that

occurs when pieces of

weathered rock sink to the

bottom of the river bed or

sea, forming sediment.


Transportation by wind

Rock particles being transported by the wind cause erosion.

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.)

Wind erosion has two

major effects:


Transportation by glacier

A glacier is a mass of ice that gradually moves overland.

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.

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.


After weathering: true or false?


Glossary


Anagrams


Multiple-choice quiz

Rocks and weathering

Science

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