Metamorphic Rocks

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Metamorphic Rock Noun

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[met-uh-mawr-fik rok]

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Metamorphic Rock

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A type of rock that forms when an existing rock is changed by exposure to high temperature and pressure.

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Example: This image shows how a sedimentary rock, shale, transforms into different types of metamorphic rocks as heat and pressure increase during the process of metamorphism.

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Plastic Deformation Noun

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[plas-tik dee-fawr-mey-shuhn]

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Plastic Deformation

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A permanent change in the shape of a rock by bending and folding, caused by heat and pressure.

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Example: This image shows three ways rocks undergo plastic deformation: folding (bending), stretching (thinning), and shearing (sliding), which are key processes in forming 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 rock comes into direct contact with a source of intense heat, such as magma.

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Example: Hot magma pushes into existing rock, and its intense heat bakes the surrounding rock layer, changing it into a new metamorphic rock.

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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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Large-scale metamorphism that occurs over a wide area, typically caused by the immense pressure from tectonic plate collisions.

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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 area into a sequence of new metamorphic rocks.

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Foliated Adjective

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[foh-lee-ey-tid]

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Foliated

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A texture in metamorphic rocks characterized by parallel layers or bands of flat and elongated minerals.

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Example: This image shows a real foliated metamorphic rock next to a diagram explaining how pressure aligns its minerals into distinct layers or bands.

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Non-Foliated Adjective

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[non-foh-lee-ey-tid]

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Non-Foliated

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A texture in metamorphic rocks where mineral grains have a random, interlocking arrangement with no parallel layers.

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Example: This image shows quartzite, a non-foliated metamorphic rock, which lacks layers or bands because its mineral grains grew in random orientations under heat and pressure.

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Foliation Noun

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[foh-lee-ey-shuhn]

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Foliation

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The appearance of parallel layers, banding, or alignment of minerals within a metamorphic rock due to directed pressure.

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Example: This image shows how pressure causes minerals in a metamorphic rock to align in parallel layers, a process called foliation.

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Rock Cleavage Noun

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[rok klee-vij]

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Rock Cleavage

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The tendency of a metamorphic rock to split or break along a single, flat plane due to intense pressure.

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Example: This image shows how a mineral breaks. Rock cleavage creates smooth, flat surfaces called cleavage planes, while a fracture creates a rough, uneven surface.

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Lineation Noun

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[lin-ee-ey-shuhn]

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Lineation

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A feature where elongated minerals become aligned in the same direction, creating a linear fabric in metamorphic rocks.

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Example: This diagram shows how a rock is stretched by geological forces, causing its mineral grains to align in a single direction, creating a linear texture called lineation.

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Parent Rock Noun

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[pair-uhnt rok]

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Parent Rock

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The original, pre-existing rock from which a metamorphic rock is formed through heat, pressure, or chemical processes.

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Example: This image shows how a parent rock, like the sedimentary rock Shale, can be transformed into a new metamorphic rock, like Gneiss, through geological processes.