What are these words?Csork

Arlctsy

Rgnia

Rtginae

Msieetnlo

Akhlc

Aelmbr

Souopr

Mianlre

Douoncmp

Rocks

Crystal

Grain

Granite

Limestone

Chalk

Marble

Porous

Mineral

Compound

1890191019401975Present day

1910 19401890

1975 today

Weathering

Learning Objectives:

• To explain why rocks break down in the environment

• To use experimental evidence to solve a problem

Weathering: The breakdown of rocks into smaller pieces by physical, chemical or biological processes

Biological: weathering caused by the activities of living organisms

Chemical: weathering caused by chemical attack on rocks

Physical: breakdown of rocks not involving chemical reactions

There is no clear distinction: the different types overlap.

These statues are both from Ancient

Egypt. Why does one look so much older?

Challenge: What is the best rock for making a statue that will last for years?

You will need to consider:

•What colour and texture will the rock have when the statue is made?

•How difficult will the rock be to carve into shape?

•Will the rock be damaged by acid rain?

Method

1. Take a sample of rock. Examine its appearance and note down any key features.

2. Using a nail scratch the rock to assess its hardness.

3. Take a small sample of the rock and place it in a watchglass. Add a few drops of sulphuric acid. Note what happens.

4. Repeat for the other types of rock.

Name of rock Appearance – what does

rock look and feel like?

Hardness Reaction with dilute acid

Which rock would you choose? Why?

1.Which two changes are caused by the acid in rainwater?

a)The writing on a gravestone disappears.b) Iron railings go rusty.c) A wooden fence post becomes rotten.d) The face of a statue loses its features.

Andrew wants to investigate the weathering of granite. He takes two pieces of granite and photographs them with a digital camera. Then he puts one piece of granite into a beaker containing strong acid and another piece into a beaker containing water.

a After two weeks Andrew removes the granite from the acid solution and examines it carefully. Why is it important to wash the rock first?

b What should Andrew compare the rock with so he can be sure it is weathered?

c Andrew is still not sure that weathering has taken place. Which additional step in his method would have helped him most to be sure? Choose from the list below.

Weigh the rock before starting the experiment.Wash the rock carefully before starting the experiment.Weigh the rock before and after the experiment.

Dry the rock carefully after the experiment.

d Katie says that Andrew should use a third piece of granite in the experiment.Why would this be a useful control for this experiment?

e Andrew photographed both rocks again after the experiment, using a digital camera. He put the images onto his computer. How could he use the images to help him decide if weathering had taken place?

• Granite contains crystals of the minerals feldspar and quartz.

• A small piece of granite is left in a solution of hydrochloric acid for a long time. The granite crumbles.

• In the material that remains, crystals of quartz are observed.

Can you explain this?

Erosion Physical, chemical or biological?

Rocks bumping into each other while travelling down a stream

Tree roots pushing against the rock

Ice getting into cracks and expanding

Acid rain

Animals or plants digging into cracks

“Onion skin weathering”

Examples of erosion…

SandstoneThe "Maltese Cross", a well-known landmark in the Cedarberg Mountains, Western Cape Province, South Africa. These hard sandstones have been sculpted into tall pillars and other fantastic shapes by weathering along the vertical cracks in the rock.

Sandstone (arkose)Precambrian red-brown sandstones, laid down by river systems 1000 million years ago, make up the bulk of the mountain Quinag, Assynt district, Sutherland, Scotland. (An arkose is a sandstone that contains a lot of feldspar in addition to quartz grains.) These steep mountains were shaped by the movement of ice sheets and glaciers over the past million years.

MudstoneThe "Finger of God", also known as Mukorob, a rock pillar in southern Namibia, photographed in 1979. A 34 metre column of sandstone rests on softer mudstone, which has eroded away to a narrow neck. The pillar eventually blew down in a storm on 4 December 1988.

Limestone weatheringMalham Cove, Yorkshire. This detailed view of the limestone pavement shows how the blocks of limestone in between the deep straight fissures have been shaped by rainwater, which has slowly dissolved curving, fluted channels as it drains off towards the deeper cracks.

Granite bouldersGranite weathers slowly, by chemical weathering. Bodies of granite commonly have only a few, widely-spaced fractures, so that a typical style of weathering produces smoothly-curved rounded shapes. These boulders of granite are about 4 metres in diameter and sit on smooth bare rock surfaces at Spitzkoppe, Namibia. In the distance are the smooth peaks of the Erongo Mountains, also made of granite.

The right side of this rock shows a fault line where water is seeping into the rock.  This will eventually cause the block to the right of the crack to cleave off,

significantly altering the shape of the rock and exposing another face to the full action of the wind driven weathering.

Remarkable rocks, Kangaroo Island, Australia

                                                        

       

The scouring caused by the wind and water action has created strange shapes like this one which is like the hooked beak of a bird.  The inside of the overhang has been eroded so that you can stand under it and look up into a cavity.

                                                        

       

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The boulders where formed by rain penetrating the granite and decomposing the rocks into blocks.  The land surface then weathered away leaving the corestones of unweathered granite.  The exposed boulders are being sculpted by wind and water forming the caves, overhangs and gullies which are present in the rocks today

The strange shapes of the rocks are caused by swirling air which when it is carrying sand and water causes the cup shaped depressions in the rocks.

                       

        

                        

        

 

These two photos show the passages which have been created as the tors (block of rock created by the weathering actions of water seeping into the cracks of the rocks).  These gaps are large enough to walk around the remarkable rocks.