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Geology. Sedimentary, igneous and metamorphic rocks contain minerals and are formed by processes that occur within Earth over a variety of timescales . What are Rocks?. A rock is a naturally occurring solid mixture of one or more minerals, or organic matter

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Sedimentary, igneous and metamorphic rocks contain minerals and are formed by processes that occur within Earth over a variety of timescales

What are rocks
What are Rocks?

  • A rock is a naturally occurring solid mixture of one or more minerals, or organic matter

  • Rocks are classified by how they are formed, their composition, and texture

  • Rocks change over time through the rock cycle

Igneous rocks1
Igneous Rocks

  • Igneous rock begins as magma.

  • Magma can form:

    • When rock is heated

    • When pressure is released

    • When rock changes composition

  • Magma freezes between

    700 °C and 1,250 °C

  • Magma is a mixture of many minerals

Igneous rocks2
Igneous Rocks

  • Coarse-grained: takes longer to cool, giving mineral crystals more time to grow (intrusive)

  • Fine-grained: cools quickly with little to no crystals (extrusive)

Igneous rocks3
Igneous Rocks







Igneous rocks4
Igneous Rocks

  • Intrusive Igneous Rocks: magma pushes into surrounding rock below the Earth’s surface

  • Extrusive Rocks: forms when magma erupts onto the Earth’s surface (lava), cools quickly with very small or no crystals formed

Igneous rocks5


What is Obsidian?

Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form.

Igneous Rocks

Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form.

Is this rock Intrusive or Extrusive?

Characteristics of igneous rocks
Characteristics of Igneous Rocks

  • Hard (because the minerals they contain are hard)

  • Strong

  • Interlocking crystals

Microscopic View of Interlocking Crystals

Igneous rocks you need to know
Igneous Rocks you NEED to Know

  • Granite

  • Basalt

  • Pumice

  • Scoria

  • Obsidian


  • 8.1 (page 285)

    • 2, 3, 5, 6a-c, 7, 8, 11, 13,

  • Complete

    • Pearson Reader Interactive Activity

    • Worksheets in Booklet

      • Describing Crystals 1 & 2

      • Igneous Rocks


  • Physical, chemical and biological process that break rocks down into smaller pieces.

Physical weathering
Physical Weathering

  • Temperature change

  • Action of Ice and Water

  • Crystallisation of Salts

  • Wind

  • Living plants (also known as biological weathering

Temperature change
Temperature Change

  • Solids _________ when heated and __________ when cooled

  • This expansion / contraction can crack a rock

Action of ice and water
Action of Ice and Water

  • Water takes up more space when frozen

  • Water in cracks in rock freezes, expands and can increase the crack size.

  • This can occur over and over again until frost shattering occurs.

  • Can also crack rocks by cooling them rapidly

  • Glaciers cause U Shaped valleys

  • Waves can weather rocks

  • Rivers can cut deep through rock forming gorges

Crystallisation of salts
Crystallisation of Salts

  • Crystals forming inside rock pores can crack them as they continue to grow

  • Salt can be formed by the evaporation of water from soil or evaporation of sea water.


  • Fine particles picked up by wind can blast the rock surface, wearing the rock away.

Biological weathering
Biological Weathering

  • Rocks are worn away by living organisms.

  • Trees and other plants can grow within the cracks in a rock formation.

  • Over time the growing tree eventually prizes the rock apart.

  • Tiny organisms like bacteria, algae and moss can grow on rocks and produce chemicals which can break down the surface layer of the rock. Burrowing animals such as rabbits can accelerate the formation of cracks.

Chemical weathering
Chemical Weathering

  • Chemicals in the air and water react with chemicals in the rock

  • Caused mostly by water, oxygen and acids.

  • The degree of chemical weathering depends on the type of rock for example limestone is more readily chemically weathered than granite. Other factors such as temperature also play a role as the chemical reactions occur more quickly in areas of high temperatures.

Natural acids
Natural Acids

  • Decay of dead plants and animals and from the rain.

  • Not very strong.

  • Limestone mostly affected – stalagmites and stalactite formation

Acid rain
Acid Rain

  • When fossil fuels such as coal, gas and gasoline are burnt they release oxides sulphur, carbon and nitrogen into the atmosphere.

  • These gases combine with moisture in the air to form sulphuric acid, carbonic acid and nitric acid, making the resulting rainwater more acidic than normal.


  • Small particles of broken rock (caused by weathering) carried away by water, wind and ice.

  • Water, wind and ice = agents of erosion

  • Takes place more so on mountains and hills….. WHY IS THIS SO?


  • Depositing of rock particles that are from another weathered rock

  • Occurs when the moving water, wind or ice slows down.

  • Where would this normally occur?


  • Sediments form basic component

  • Also made of:

    • bacteria and fungi,

    • decaying wastes,

    • dead leaves,

    • twigs and insects,

    • water,

    • dissolved minerals and gases

Sedimentary rocks1
Sedimentary Rocks

  • Sedimentary rock is formed by erosion and deposition

  • Sediments are moved from one place to another (erosion)

  • Sediments are deposited in layers, with the older ones

  • on the bottom (deposition)

  • The layers become compacted and cemented together

Sedimentary rock
Sedimentary Rock

  • Sedimentary Rocks are formed at or near the Earth’s surface

  • No heat and pressure involved

  • Strata – layers of rock

  • Stratification – the process in which sedimentary rocks are arranged in layers

Types sedimentary rock from pieces of weathered rock
Types Sedimentary Rock – From Pieces of Weathered Rock

Clastic – made of fragments of rock cemented together with calcite or quartz

Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter).

The spaces between the large angular fragments can be filled with a matrix of smaller particles or a mineral cement that binds the rock together.

Sedimentary rock types dead animal or plant material
Sedimentary Rock Types – Dead Animal or Plant Material

Organic or Biological Sedimentary – remains of plants and animals

Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment. 

Coal is a combustible rock and along with oil and natural gas it is one of the three most important fossil fuels. 

Sedimentary rock from minerals crystallisaing from solution
Sedimentary Rock – From Minerals Crystallisaing from Solution

Chemical sedimentary – minerals crystallize out of solution to become rock

Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters.

It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris.

Sedimentary rocks you need to know
Sedimentary Rocks you SolutionNEED to Know

  • Sandstone

  • Mudstone

  • Siltstone

  • Conglomerate

  • Limestone

  • Coal

  • Chalk

Metamorphic rock
Metamorphic Rock Solution

  • Meaning to change shape

  • Changes with temperature

  • and pressure, but remains

  • solid

  • Usually takes place deep in

  • the Earth

Metamorphic rocks1
Metamorphic Rocks Solution

  • Contact Metamorphism – heated by nearby magma

  • Increased temperature changes the composition of the rock, minerals are changed into new minerals

Hornfels is a fine-grained non-foliated metamorphic rock produced by contact metamorphism

Metamorphic rocks2
Metamorphic Rocks Solution

  • Regional Metamorphism – pressure builds up in rocks that is deep within the Earth

  • Large pieces of the Earth’s crust collide and the rock is deformed and chemically changed by heat and pressure

Comparison Solution

Metamorphic rock1
Metamorphic Rock Solution

  • Foliated - contain aligned grains of flat minerals

Gneiss is foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains.

It typically contains abundant quartz or feldspar minerals.

Metamorphic rock2
Metamorphic Rock Solution

  • Non-Foliated or Unbanded – mineral grains are not arranged in plains or bands

Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone.

It is composed primarily of calcium carbonate.

Metamorphic rocks you need to know
Metamorphic Rocks you SolutionNEED to Know

  • Slate (from shale or siltstone)

  • Marble (from limestone)

Rock cycle
Rock Cycle Solution

  • Model geologist use to explain the endless cycle that rocks undergo.

  • Rocks don’t always remain the same ‘type’ after they are formed

Fossils Solution

  • Fossils allow palaeontologists to build a history of the Earth

  • Fossils:

    • Remains or imprints of animals and plants preserved in rock

    • Rare

    • Right circumstances


Geologic time
Geologic Time Solution

  • The older the rock the simpler the fossil..

    • Why is this the case?

    • The variety and complexity of life has increased as the Earth has become older.

Comparative dating relative
Comparative Dating (Relative) Solution

  • Sedimentary rocks – youngest rocks at the top, oldest at the bottom.

  • Different rocks of the same age have the same fossils in them

    • Called guide or index fossils