Rocks

What feature does gneiss have?

Gneiss has alternating bands of black and white

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Sandstone has layers of different sized grains of sand

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Crystals are small pieces or organized particle, usually with smooth sides and edges and one colour

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Grains are small pieces of material. The size of grain can be used to identify rocks

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Large grains are course, grains that are small but can be seen with the naked eye are called medium grained and grains that cannot be seen without a microscope are called fine

2.2

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A mineral is a naturally occurring, inorganic, solid substance with its own chemical composition, structure and properties

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Minerals are found from crystals

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Types of lustre are metallic, brilliant, pearly, dull and earthy

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Lustre is the shininess of the surface of a mineral

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Hardness is how easily a mineral can be scratched

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Streak is the colour of the powdered or crushed mineral

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Cleavage is the tendency of a mineral to break into a number of smooth planes

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Minerals that demonstrate cleavage look like thin slabs together

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Mineral properties include lustre, colour, streak, hardness and cleavage

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Mohs scale of hardness is used as a relative measurement of hardness

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Carbon exists as coal, graphite and diamond (each have different bonding based on chemical bonding)

2.3

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Ores are minerals that contain large amounts of useful metals

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Bauxite contains aluminium

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Haematite contains iron

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Malachite contains copper

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Copper is found as the mineral chalcopyrite in rocks

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Copper can be used for water pipes and electrical wires

2.4

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The earth is made up of the inner and outer core, mantle and crust

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Magma is very hot liquid rock

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Magma erupts from volcanoes and flows as lava

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Lava cools and solidifies to form igneous rock

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Fast cooling of magma causes small crystals in igneous rocks (called extrusive rocks)

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Slow cooling of magma causes large crystals in igneous rocks (called intrusive rocks)

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Intrusive rocks form under the earth’s surface but can be seen on the surface due to erosion and uplift e.g. granite, gabbro, diorite

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Lava cools quickly on the surface to form extrusive rocks e.g. basalt, obsidian, pumice

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Igneous rocks are composed of interlocking crystals

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Igneous rocks can be classified by colour and texture

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The three main types of rocks are igneous, sedimentary and metamorphic

2.5

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Sedimentary rocks are formed when loose particles of sediment are compacted and cemented together

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Clastic sedimentary rocks result from pieces of weathered rock e.g. conglomerate

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Chemical sedimentary rocks result from minerals crystallising out of solutions e.g. rock salt

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Organic sedimentary rocks result from dead plant matter and animal debris e.g. coal

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Limestone caves are formed when dissolved calcium carbonate crystallise

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Conglomerate rocks are formed from rocks of different sizes compacted together

2.6

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Metamorphic rocks are formed from intense heat and pressure altering existing igneous and sedimentary rocks or other metamorphic rocks

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Changes can be physical or chemical and can result in the formation of new minerals

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Heat and pressure cause rocks to melt which then recrystallises to form metamorphic rocks e.g. marble, slate, gneiss

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Gemstones are found in metamorphic rocks

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Limestone forms marble, granite forms gneiss, shale forms slate

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When rock crystals twist it is called foliation

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Foliation may occur when forming metamorphic rocks

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Sillimanite, kyanite and garnet are metamorphic minerals

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Metamorphic minerals only form at high temperatures and pressures, which are called index minerals

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Heat and temperature can cause some crystals to change their size and shape

2.7

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Examples of physical weathering are temperature change (onion skin), ice and water (frost shattering), crystallisation of salt, wind and living plants

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Chemical weathering results from water and chemicals in the water and air reacting with rock e.g. acid in rain

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Biological weathering includes the effect of plant roots on rocks

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Particles of rock from weathering can be moved to other areas by water, wind and ice (called erosion)

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The particles can be deposited, which is called sedimentation

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Weathering is the breakdown of ro0cks

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Erosion is the removal of rock material

2.8

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Human actions e.g. removal trees can affect weathering

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To prevent weathering building e.g. dams, levees, groynes, terraces, expansion gaps in footpaths

2.9

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Geologists study the structure and changes of the earth

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Fossils are remains/traces of dead organisms

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Comparative dating determines the age of an organism relative to others based on their strata in sedimentary rock

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Radioactive dating uses the amount of radioactivity is a substance to find its age

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Fossils are formed by the deposition of layers of sediment

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Uranium decays to lead so as rocks age, amount of uranium decreases and lead increases