Sedimentary, igneous and metamorphic rocks contain minerals and are formed by processes that occur...
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Transcript of Sedimentary, igneous and metamorphic rocks contain minerals and are formed by processes that occur...
Sedimentary, igneous and metamorphic rocks contain minerals and are formed by processes that occur within Earth over a variety of timescales
Geology
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 Rocks
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 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 Rocks
Coarse-Grained
Fine-Grained
Granite
Gabbro Basalt
Rhyolite
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 Rocks
Obsidian
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.
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
• Hard (because the minerals they contain are hard)
• Strong• Interlocking
crystals
Microscopic View of
Interlocking Crystals
Uses of Igneous Rocks
Igneous rock Use
Basalt Buildings (for example Melbourne bluestone), concrete (as crushed rock), floor tiles
Dolerite Road surfaces (where it is called 'blue metal'), concrete (as crushed rock)
Granite Buildings, monuments, road surfaces, kitchen benchtops
Scoria Landscaping, filters and concrete (all as crushed rock), barbecue rocks
Pumice Cleaning dead skin off feet, emery boards for shaping nails, some soaps that feel rough on your skin
ObsidianScalpel blade for surgery in hospitals, ornaments and jewellery. Ancient people used it for cutting, spear and arrow points, and pots and vases
Igneous Rocks you NEED to Know
•Granite•Basalt•Pumice•Scoria
•Obsidian
Requirements
• 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
Weathering
Weathering• Physical, chemical and biological process that
break rocks down into smaller pieces.
Physical Weathering• Temperature change
• Action of Ice and Water
• Crystallisation of Salts
• Wind
• Living plants (also known as biological weathering
Temperature Change
• Solids _________ when heated and __________ when cooled
• This expansion / contraction can crack a rock
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• 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.
Wind• Fine particles picked up by wind can blast the rock
surface, wearing the rock away.
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 • 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• Decay of dead plants and animals and from the
rain. • Not very strong.• Limestone mostly affected – stalagmites and
stalactite formation
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.
Erosion• 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?
Sedimentation• 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?
Soil• Sediments form basic component• Also made of: • bacteria and fungi, • decaying wastes, • dead leaves, • twigs and insects, • water, • dissolved minerals and gases
Sedimentary Rocks
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 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
Clastic – made of fragments of rock cemented together with calcite or quartzBreccia 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
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
Chemical sedimentary – minerals crystallize out of solution to become rockLimestone 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.
Uses of Sedimentary RocksSedimentary Rock Use
Limestone Garden WallsPavingBuildingsMaking cement, glass and steel
Sandstone BuildingsFlooringDecorative OrnamentsWallsMaking glass
Gypsum Making plaster
Coal Energy supply
Sedimentary Rocks you NEED to Know
• Sandstone•Mudstone• Siltstone
• Conglomerate • Limestone• Coal• Chalk
Metamorphic Rocks
Metamorphic Rock
Meaning to change shape
Changes with temperature and pressure, but remains solid
Usually takes place deep in the Earth
Metamorphic Rocks
• 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 Rocks
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
Metamorphic Rock• 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 Rock• 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.
Uses of Metamorphic Rocks
Name of Rock Use
Slate FlooringRood tiling
Marble Buildings Sculptures
Metamorphic Rocks you NEED to Know
•Slate (from shale or siltstone)
•Marble (from limestone)
Rock Cycle • Model geologist
use to explain the endless cycle that rocks undergo.
• Rocks don’t always remain the same ‘type’ after they are formed
Fossils• Fossils allow palaeontologists to build a history of
the Earth• Fossils:• Remains or imprints of animals and plants preserved in
rock• Rare• Right circumstances
required
Geologic Time• 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)• 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