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Geology: Igneous Rocks
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Pyroclastic rock is formed by
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Igneous rocks are formed by the crystallization of magma.
When magma cools beneath the surface of the earth it makes intrusive igneous rock, such as granite. The magma is insulated by the surrounding rock, and cools slowly. This allows the crystals in the rock a long time to form, creating large crystals.
When magma erupts onto the earth's surface, it becomes larva in a volcanic eruption. Larva cools and turns to rock relatively quickly. The crystals in the rock don't have much time to form, creating fine-grained rocks with small crystals, such as basalt.
When there's an explosive volcanic eruption, ash is thrown high into the air. Where this ash falls and turns into rock, it's called pyroclastic rock.
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