Q:

Where do rocks come from?

A:

Quick Answer

Rocks come from magma, which is the molten material found within the earth. When magma cools, either above or below the earth's surface, it crystallizes and forms the igneous rocks that can later be changed into metamorphic or sedimentary rocks. Magma, which can be considered molten rock, is referred to as lava when it reaches the earth's surface.

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Where do rocks come from?
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The igneous rocks initially formed from cooled and crystallized magma can eventually be weathered down into fragments by the forces of erosion. They then become sedimentary rocks through the additional processes of compaction and cementation. Both igneous and sedimentary rocks can be transformed into metamorphic rock when subjected to pressure and temperature conditions other than those which originally formed them. Heat is produced by the friction generated by movements of Earth's tectonic plates, and the creation of mountains creates pressure. An intrusion of magma into surrounding rock can also be a source of heat. Overall, the temperatures and pressures needed to produce metamorphic rocks are much greater than those found on the earth's surface.

Each of the three major classes of rock can be transformed into one of the other classes through the continuing processes of heat, pressure and erosion. This ongoing transformation of rocks is referred to as the rock cycle.

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Related Questions

  • Q:

    Which type of magma has the greatest silica content?

    A:

    Rhyolitic magma has the greatest silica content, with silica making up about 70 percent of the magma. Basaltic and andesitic magma have lower silica contents at 50 percent and 60 percent, respectively.

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  • Q:

    What rock is formed when magma cools at the Earth's surface?

    A:

    The specific type of rock that forms when magma cools at the Earth's surface is extrusive igneous rock. Igneous rock forms when magma cools, but where the magma cools determines the type of igneous rock that forms. Igneous rock gets its name from the Greek word for fire and is so called due to the extremely hot liquid from which the rocks originate.

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  • Q:

    How is a laccolith formed?

    A:

    A laccolith is a geological structure that forms when magma pushes through layers of rock above it and pools in a dome shape. Laccoliths are characterized by their shape, as they are typically flat on the bottom and rounded or dome shaped on top. These structures are also called plutonic formations or igneous intrusions, which are related to sills.

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  • Q:

    Why is Earth geologically active?

    A:

    Earth is geologically active because its internal heat keeps the outer core and lithosphere molten, encouraging plate movement and volcanic activity. Earth's crust consists of tectonic plates floating atop the malleable mantle, which in turn rises and falls over the semi-liquid outer core. The intense heat forces molten rock up toward the surface, creating new crust and driving intense geologic activity.

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