Types of Rock

© Boardworks Ltd 2003

Types of Rock

There are 3 types of rock:

Sedimentary

Metamorphic

Igneous


Sedimentary Rock – Deposition

Small particles of rock formed by weathering are transported into the sea where they are deposited (sink) and form a sediment.

At this stage dead creatures may become trapped within the sediment giving rise to fossils.

Over millions of years, the pressure of the layers formed above and the effects of salts cement the sediment together to give sedimentary rocks like sandstone and mudstone.

Fast flowing water

Slow water

Pressure

sedim

entatio

ncem

entatio

n


Sedimentation + effects of pressure and minerals.

Layers of sedimentsgetting older

Sedimentary Rock – Sedimentation


Sedimentary Rock - Evaporation

Some sedimentary rock is formed in a different way.

Certain minerals are dissolved in seas and lakes.

Over millions of years these seas or lakes have dried up.

As the water disappeared the dissolved minerals precipitated.

Chalk and limestone, common in the UK, are often formed in this way.

Dissolved minerals

Precipitation

Pressure

evapo

ration


Sedimentary Rock - appearance

Sedimentary rocks consist of lots of small particles and may be soft and crumbly

They do not normally contain crystals but may have fossilsfossils trapped within them.

When viewing a whole cliff face of sedimentary rock it is often possible to see layers where slightly different sediments have been deposited.

Sedimentary rocks consist of lots of small particles.


Sedimentary Rocks

sandstone

limestone chalk

sandstone


sandstone

orangey coloured rock

looks like lots of sand grains stuck together

quite soft


limestone

grey/white coloured rock

mostly made from crushed sea-shells

may contain fossilised shells


chalk

grey/white coloured rock.

mostly made from crushed sea-shells

may contain fossilised shells


Match the rock with the description:

Rock PictureSandstone

Limestone

Mudstone and shale

Chalk


Metamorphic Rock - formation

Metamorphic rocks are formed by the effect of extreme pressures and temperatures deep within the Earth.

This alters the structure of the existing rock.


Metamorphic Rock - properties

They are usually denser and harder than sedimentary rocks.

They often have layerlayer structures of crystals caused by the effect of heat and pressure.

They sometimes show distortions caused by the movements that led to their formation. This may give rise to wavy or zig-zag patterns within the rock.

Regular layers of crystals that sometimes also have a wavy or zig-zag arrangement


Metamorphic Rocks

marble

slate

Enlargements on next two slides


marble

High temperatures cause the shells in limestone to break down into crystals giving a harder smoother rock.


slate

Pressure and some heat makes the particles in mudstone line up in one direction. This makes a rock that can be split into sheets.


Which description goes with the rock?

Description Rock

Dark grey rock used for roofing because it is easily split into thin layers.

Marble

Smooth, hard white rock often used for kitchen cutting “boards.”

Mica

Transparent sheets are used as an insulator in some electrical devices. It is also ground up and used as a “filler” in plastics, and cosmetics such as lipsticks.

Slate


Igneous Rocks - Formation

Deep within the ground is molten rock called magma. Sometimes this bursts through the surface in the form of volcanoes.

Igneous rocks are formed when molten magma cools and solidifies.

This may happen within the ground, or in the case of volcano lava, above ground.

magma

intrusive igneous rock

extrusive igneous rock


Igneous Rocks – Rate of Solidification

The appearance of igneous rocks is affected by how fast they cool.

Rocks formed within the ground are known as intrusive igneous rocks . They cool slowly and this gives time for large crystals to grow.

Rocks formed once the magma has burst through the surface are called extrusive igneous.

They cool quickly.

As a result crystals are much smaller.


Igneous Rocks - intrusive

granite

A hard grey rock consisting of randomly arranged crystals.


pumice

Extrusive igneous rocks, like pumice and basalt, do not have large crystals and tend to be less dense than intrusive rocks like granite.

Igneous Rocks - extrusive


basalt - pillars

Igneous Rocks - extrusive


Igneous Rocks – Properties

Igneous rocks are hard.

They contain crystals. The the size of the crystals depends on how quickly the rock solidified.

The crystals are disordered (unlike some metamorphic rocks.)

They never contain fossils.

Igneous rocks consist of a disorderly collection of crystals


Am I igneous, sedimentary or metamorphic?

sedimentary

igneous (ext)

metamorphic

sedimentarysedimentary

igneous (intr)

metamorphic

Type

I contain many fossils.

I am pumice.

My particles are arranged in bands that are easily split apart.

I contain many small grains “cemented” together.

I am mudstone.

I contain some really big crystals.

I am formed by heat and pressure.

Description


Rock Formation

sea

volcano

Igneous rocksbasalt

Igneous rocksgranites

rocks riseto surface by

uplift and erosion

rocks are brokenup by the action

of weather

magma

Metamorphic rocks slate and marble

Sedimentary rocksmudstone

slowsolidification

high pressureand temperature

transportationand deposition

rises to surfacewhere it

cools rapidly

melt


• Rocks take part in a rock cycle.• Molten ___________ solidifies at or near the

surface of the Earth to form ___________ rocks.

• These undergo ___________ where they are broken up by ___________ and chemical processes.

magma

igneous

weathering

physical

Fill in the gaps in the sentences.

magma

igneous

weathering

physical

sedimentary

metamorphic


• The fragments of rock are carried to the ___________ by rivers. Here they sink and form ___________ rocks.

• Over millions of years heat, ___________ and movement may change these sedimentary rocks into ___________ rocks. Some of these will sink deep into the Earth and turn into ___________ and the cycle is repeated.

sea

sedimentary

pressure

metamorphic

magma

Fill in the gaps in the sentences.

magma

igneous

pressure

sea

sedimentary

metamorphic


What type of rocks do these diagram represent?

igneous metamorphic sedimentary


A Intrusive Igneous

B Extrusive Igneous

C Metamorphic

D Sedimentary

1. What type of rock is granite?


A Intrusive Igneous

B Extrusive Igneous

C Metamorphic

D Sedimentary

2. What type of rock is slate?


A Intrusive Igneous

B Extrusive Igneous

C Metamorphic

D Sedimentary

3. What type of rock is limestone?


A Intrusive Igneous

B Extrusive Igneous

C Metamorphic

D Sedimentary

4. What type of rocks are pumice and basalt?


A Intrusive Igneous

B Extrusive Igneous

C Metamorphic

D Sedimentary

5. What type of rock is mudstone?


A Pumice

B Limestone

C Slate

D Granite

6. What type of rocks is made from mudstone or shale?


A 1

B 2

7. In this diagram showing a cross section of a volcano, where would granite form?

1

2

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Types of Rock