Unit 1: Rocks and minerals and their exploitation
1.1 Formation of rocks
● Planet Earth was formed 4.5billion years ago
● The force of gravity pulled heavier elements first, forming the core. The lighter then
formed the crust. The mantle developed as a layer between the dense core and the
light crust.
Igneous rocks
● When molten rock (magma below the surface and lava when it reaches the surface)
and upper mantle cools, igneous rocks are formed.
● Magma is found in the outer mantle, it’s hot liquid rock that is under pressure from
the rocks above it. When it cools it forms a solid rock.
● When liquid magma rises to the surface from volcanoes, it forms lava quickly.
● Usually, igneous rocks contain crystals that are formed as the molten material cools.
● Crystals are formed when solutions of minerals can’t absorb any more dissolved
minerals.
● Some of each mineral type precipitates out of solution to form the centre of a
crystal. This provides a surface for more mineral ions to precipitate onto. The crystal
becomes larger until the solution disappears.
● If rocks cool quickly, only small crystals can be formed. (e.g. rapid cooling of magma
when released from volcanoes).
● If magma rises from the mantle into the crust without reaching the surface, then it
cools slowly, allowing the formation of larger crystals. Some of them are used in
industrial processes
● Heat and pressure are the usual reasons for minerals becoming dissolved, a
reduction of heat and pressure leads to the formation of crystals.
● (e.g. granite, basalt)
Sedimentary rocks
● Formed by the weathering of existing rocks at the Earth’s surface, the accumulation
and fossilisation of dead plants and animals, or the precipitation of dissolved
materials out of solution in water.
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, ● Weathering processes release small mineral particles that accumulate to form
sediment. Over time, layers of sediment build up to form sedimentary rocks.
● Sediments include different sized mineral particles, the smallest are clays, silts and
then sands. These are important in the formation of soils.
● The particles are transported by streams and rivers, and then deposited as sediment,
each layer becomes more compact and harder because of the pressure being built.
● (e.g. limestone, sandstone, shale)
Metamorphic rocks
● Created from existing rocks when heat (above 150°C) and/or pressure (above 1480
atm), causes changes in the rock crystals without melting the existing rock.
● The rock changes in structure, these changes can be chemical or physical or both.
● Sedimentary and igneous rocks can become metamorphic rocks, and a metamorphic
rock can become another metamorphic rock. These ones are usually harder than
sedimentary ones.
● (e.g. marble, slate)
When the Earth’s crust first formed, all rocks were igneous. These rocks slowly eroded and
formed sedimentary rocks. The rocks that make up Earth’s crust are always moving, which
creates heat and pressure for metamorphic rocks to form. All rock types are constantly
eroded and formed in the rock cycle.
Igneous Sedimentary Metamorphic
Made from liquid magma Made from other rock Made from existing rocks
fragments
Magma cools to form solid Rock fragments become The original rock is
rock buried and increased changed in form by heat
pressure forms a rock and pressure
Mineral crystals Crystals absent Crystals present
sometimes present, the
size of the crystals
depends on the speed of
cooling
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1.1 Formation of rocks
● Planet Earth was formed 4.5billion years ago
● The force of gravity pulled heavier elements first, forming the core. The lighter then
formed the crust. The mantle developed as a layer between the dense core and the
light crust.
Igneous rocks
● When molten rock (magma below the surface and lava when it reaches the surface)
and upper mantle cools, igneous rocks are formed.
● Magma is found in the outer mantle, it’s hot liquid rock that is under pressure from
the rocks above it. When it cools it forms a solid rock.
● When liquid magma rises to the surface from volcanoes, it forms lava quickly.
● Usually, igneous rocks contain crystals that are formed as the molten material cools.
● Crystals are formed when solutions of minerals can’t absorb any more dissolved
minerals.
● Some of each mineral type precipitates out of solution to form the centre of a
crystal. This provides a surface for more mineral ions to precipitate onto. The crystal
becomes larger until the solution disappears.
● If rocks cool quickly, only small crystals can be formed. (e.g. rapid cooling of magma
when released from volcanoes).
● If magma rises from the mantle into the crust without reaching the surface, then it
cools slowly, allowing the formation of larger crystals. Some of them are used in
industrial processes
● Heat and pressure are the usual reasons for minerals becoming dissolved, a
reduction of heat and pressure leads to the formation of crystals.
● (e.g. granite, basalt)
Sedimentary rocks
● Formed by the weathering of existing rocks at the Earth’s surface, the accumulation
and fossilisation of dead plants and animals, or the precipitation of dissolved
materials out of solution in water.
Página 1 | 8
, ● Weathering processes release small mineral particles that accumulate to form
sediment. Over time, layers of sediment build up to form sedimentary rocks.
● Sediments include different sized mineral particles, the smallest are clays, silts and
then sands. These are important in the formation of soils.
● The particles are transported by streams and rivers, and then deposited as sediment,
each layer becomes more compact and harder because of the pressure being built.
● (e.g. limestone, sandstone, shale)
Metamorphic rocks
● Created from existing rocks when heat (above 150°C) and/or pressure (above 1480
atm), causes changes in the rock crystals without melting the existing rock.
● The rock changes in structure, these changes can be chemical or physical or both.
● Sedimentary and igneous rocks can become metamorphic rocks, and a metamorphic
rock can become another metamorphic rock. These ones are usually harder than
sedimentary ones.
● (e.g. marble, slate)
When the Earth’s crust first formed, all rocks were igneous. These rocks slowly eroded and
formed sedimentary rocks. The rocks that make up Earth’s crust are always moving, which
creates heat and pressure for metamorphic rocks to form. All rock types are constantly
eroded and formed in the rock cycle.
Igneous Sedimentary Metamorphic
Made from liquid magma Made from other rock Made from existing rocks
fragments
Magma cools to form solid Rock fragments become The original rock is
rock buried and increased changed in form by heat
pressure forms a rock and pressure
Mineral crystals Crystals absent Crystals present
sometimes present, the
size of the crystals
depends on the speed of
cooling
Página 2 | 8
