Crystal size in igneous rocks is determined by ?A.the speed of tectonic plate movement.B.the type of magma emplacement.C.magma composition.D.the rate melted rock cools.
Question
Crystal size in igneous rocks is determined by ?A.the speed of tectonic plate movement.B.the type of magma emplacement.C.magma composition.D.the rate melted rock cools.
Solution
The size of crystals in igneous rocks is determined by D. the rate at which the melted rock cools.
Here's a step-by-step explanation:
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Igneous rocks form when magma (molten rock) cools and solidifies.
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The rate at which this cooling occurs greatly influences the size of the crystals that form within the rock.
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If the magma cools slowly, usually deep underground, the crystals have a longer time to grow and become larger. This results in a coarse-grained texture, visible to the naked eye. This type of igneous rock is called intrusive.
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If the magma cools quickly, usually near the Earth's surface as in the case of a volcanic eruption, the crystals do not have much time to grow and are often too small to be seen without magnification. This results in a fine-grained texture. This type of igneous rock is called extrusive.
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Therefore, the size of the crystals in igneous rocks is not determined by the speed of tectonic plate movement, the type of magma emplacement, or the magma composition, but by the rate at which the magma cools.
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