Earth's Interior

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Metamorphism Noun

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[met-uh-mawr-fiz-uhm]

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Metamorphism

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The process of change in which a rock is transformed by heat, pressure, or chemical reactions.

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Example: Heat from a magma chamber alters nearby rock layers, transforming sedimentary rocks like limestone and shale into new metamorphic rocks like marble and hornfels.

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Regional metamorphism Noun

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[ree-juh-nl met-uh-mawr-fiz-uhm]

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Regional metamorphism

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Metamorphism that occurs over a broad volume of rock, typically happening deep underground.

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Example: This diagram shows how immense pressure from colliding tectonic plates and increasing heat with depth transform rocks over a large region, forming new metamorphic rocks.

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Contact metamorphism Noun

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[kon-takt met-uh-mawr-fiz-uhm]

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Contact metamorphism

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Metamorphism that occurs when magma rises up through and makes contact with cold rock.

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Example: When hot magma (an igneous intrusion) pushes into existing cool rock, its intense heat bakes and changes the rock it directly touches, forming a new metamorphic rock.

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Foliated Adjective

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[foh-lee-ey-tid]

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Foliated

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The texture of metamorphic rocks with crystals arranged in parallel layers or bands.

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Example: This image shows a foliated metamorphic rock. The visible layers or bands are formed when heat and pressure deep inside Earth cause minerals to flatten and line up.

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Nonfoliated Adjective

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[non-foh-lee-ey-tid]

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Nonfoliated

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The texture of metamorphic rocks where crystals are arranged randomly and do not have bands.

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Example: This image shows a nonfoliated metamorphic rock. Notice how the mineral crystals are randomly arranged and there are no visible layers or bands.

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Gneiss Noun

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[nahys]

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Gneiss

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A foliated metamorphic rock with obvious banding of light- and dark-colored minerals.

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Example: This image shows that Gneiss is a metamorphic rock, recognizable by its bands, formed from a parent rock like Shale through heat and pressure.

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Schist Noun

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[shist]

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Schist

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A foliated metamorphic rock with a similar composition to gneiss but without obvious banding.

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Example: This diagram shows that Schist is a metamorphic rock formed under intermediate temperature and pressure, as part of a sequence from lower-grade to higher-grade rocks.

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Rock cycle Noun

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[rok sahy-kuhl]

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Rock cycle

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A series of processes in which rocks continuously change from one type to another.

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Example: This diagram shows how rocks change type through processes like melting into magma, cooling into igneous rock, and being altered by heat and pressure.

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Plate tectonics Noun

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[pleyt tek-ton-iks]

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Plate tectonics

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The theory that pieces of Earth's lithosphere, called plates, move about slowly on top of the asthenosphere.

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Example: This diagram shows a convergent plate boundary, where two of Earth's tectonic plates collide, causing one to slide under the other, which can form volcanoes.

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Lithosphere Noun

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[lith-uh-sfeer]

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Lithosphere

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The rigid outer part of the Earth, consisting of the crust and upper mantle, which is broken into plates.

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Example: This diagram shows the Lithosphere as the rigid outer layer of the Earth, which includes the crust and the solid uppermost part of the mantle.