Igneous Rocks

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Why are they called igneous rocks?
The word "igneous" comes from the Latin for fire and this fits because igneous rocks come from magma.
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What percentage of the Earth’s crust do they make up?
Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earth's crust
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How are igneous rocks classified?
They are classified by minerals present in the rock, texture of the rock, colour and chemical composition.
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Why is the rate of cooling so important?
The size of the crystals depends on how quickly the molten magma solidified. The more slowly the magma cools, the bigger the crystals.
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Why is there so much silica in igneous rocks?
Igneous rocks are composed almost entirely of silicate minerals because of the abundance of the components oxygen and silicon, oxygen and silicon make up around 60% of the earth.
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What do the terms felsic, intermediate and mafic mean?
Mafic rocks are dominated by plagioclase and pyroxene and smaller amounts of olivine. Intermediate rocks are roughly even mixtures of felsic minerals and mafic minerals. Felsic rocks are mostly feldspar, at least 10% quartz and > 15% mafic minerals.
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What does acidic and basic mean?
acidic is if the rock has a low pH and basic means that it has a high pH therefore is more alkali.
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What percentage of the Earth’s crust do they make up?

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Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earth's crust

Card 3

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How are igneous rocks classified?

Back

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Card 4

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Why is the rate of cooling so important?

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Card 5

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Why is there so much silica in igneous rocks?

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