Detailed notes that summarise the Geography IEB syllabus of Rocks. Included in these notes are important definitions and concepts to learn as well as diagrams that make the section more understandable.
Rock
• Rocks are made from minerals
• A mineral is a naturally occurring inorganic substance
• Rocks have a speci c chemical and crystal structure
• Some rocks are made from many minerals and others of only two
Igneous roc
• The word igneous derives from the latin word for FIRE
• They are made from magma
intrusive igneous rock extrusive igneous rock
large crystals- coarse grains small crystals- ne grained
slow cool- inside crust cools quickly
Characteristics
• They are massive- i.e. they have no layers
• However when the rock cools it shrinks a little and this forms cracks
and joints- this is when weathering will occur
• Fine to coarse grained rocks
• Made of different minerals and have beautiful colours
• They are very hard and resistant to erosion
Use
• kitchen counters
• sculptures
• fertile soil when eroded
• valuable minerals
Example
• Gabbro
• Andesite
• Granite
• Top layers of the Drakensberg mountains-basalt (lava ow-grain:
small)
• Karoo cap rock- dolerite (larger grains- formed underground)
• Paarl rock- Granite (batholith formed far below the surface-crystals:
large)
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, Sedimentary Roc
• Most rocks on the earth are sedimentary rocks
Clastic sedimentary rock
Weathering- the process whereby rocks are broken down into smaller
and smaller particles through exposure to the atmosphere
Broken material is washed into rivers
Erosion- the process whereby material is broken down and transported
by win, water and ice
Clastic sediments- particles- small stones, pebbles, sand, mud,
soil, clay- are deposited on lake bed or sea oor
Pressure called lithi cation- build up of sediments leads to
pressure and the under lying layers are compressed
Organic Sedimentary rock
• These are formed from the remains of dead plant and animals
• They often contain fossils EG. Coal
• They are found in swampy areas. Therefore plants decay where there
is no oxygen or microbes
• Peat is a dark, soft substance. Plants die in the swamp, sediments are
deposited in the swamp. The weight of the overlying sediments
compresses the organ matter to form peat
• Further compression squeezes the water out and causes the peat turn
into coal
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