Igneous Rocks Flashcards
What are igneous rocks?
Igneous rocks are produced through the crystallisation of magma.
- They are usually strong.
- Too hot to contain the remains of life forms.
- Characterised by composition and crystal size.
- They are usually formed in or near plate boundaries.
What are intrusive / extrusive igneous rocks?
- Intrusive = Solidify slowly in the Earth’s mantle meaning crystals are large.
- Extrusive = Solidify quickly at the Earth’s surface meaning crystals are small and glassy.
What are pyroclasts?
- Sometimes in volcanoes, fine material is thrown into the air forming pyroclasts.
- If this material is fine, it will solidify in the air with very little crystal forms meaning the material is very glassy (known as volcanic ash).
- This ash can be transported around the Earth, and when it settles, pumice is formed.
- This pumice settles in layers which can sometimes be confused with sedimentary rocks.
What are felsic / mafic igneous rocks?
Felsic = Lightly coloured rocks.
- Dominated by silica and feldspar.
- Have a low density and melting point but high viscosity.
- High silica content.
Mafic = Dark coloured rocks.
- Dominated by magnesium and olivine.
- Have a high density and melting point but low viscosity.
- Low silica content.
How are polarising microscopes used?
- They take thin slices of rock and shine polarised light through, where crystals act as polarising lenses.
- This produces dark and light patterns which help you to see the rock structure.
What are the different features of magma inside the crust?
- Dike = a vertical wall of intrusive magma.
- Sill = a horizontal wall of intrusive magma, contained within the different layers of sedimentary rock.
- Batholith = a large volume of intrusive magma deep in the Earth’s crust.
- Pluton = a smaller volume of intrusive magma deep in the Earth’s crust.
What type of igneous rocks are found near the different plate boundaries?
Divergent plate boundaries:
- Forms a mid-ocean ridge made up of material from the mantle.
- Rocks found here are therefore mafic extrusive/intrusive igneous rock.
Hot spot volcanos:
- Form a volcano made up of material from the mantle.
- Rocks found here are therefore mafic extrusive/intrusive igneous rock.
Oceanic / continental subduction zone:
- Form continental volcanos made up of material from the melted subducted plate which has continental crust deposited on it.
- Rocks found here are therefore felsic extrusive/intrusive igneous rock.
Oceanic / oceanic subduction zone:
- Form oceanic volcanos made up of material from the melted subducted oceanic plate.
- Rocks found here are therefore felsic extrusive/intrusive igneous rock.
What are the features of granite?
Granite is a coarse, intrusive igneous rock.
- Felsic.
- Dominated by Quartz and Orthoclase.
- High silica and sodium content.
- High viscosity but low density and melting point.
What are the features of rhyolite?
Rhyolite is a fine, extrusive igneous rock.
- Felsic.
- Dominated by Quartz and Orthoclase.
- High silica and sodium content.
- High viscosity but low density and melting point.
What are the features of Gabbro?
Gabbro is a coarse, intrusive igneous rock.
- Mafic.
- Dominated by Plagioclase and Pyroxene.
- Low silica and sodium content.
- Low viscosity but high density and melting point.
What are the features of Basalt?
Basalt is a fine, extrusive igneous rock.
- Mafic.
- Dominated by Plagioclase and Pyroxene.
- Low silica and sodium content.
- Low viscosity but high density and melting point.
What are the features of Peridotite?
Peridotite is a coarse, intrusive igneous rock.
- Ultramafic.
- Dominated by Olivine and Pyroxene.
- Very low silica and sodium content.
- Very low viscosity but high density and melting point.
What is the igneous rock diagram?
