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Metamorphic rocks are created when existing rocks transform under extreme heat and pressure deep within Earth's crust. Unlike igneous rocks (formed from molten magma) or sedimentary rocks (made from compressed sediments), metamorphic rocks change while remaining solid. This process, called metamorphism, alters both the texture and mineral composition of the original rock.
Heat and Pressure: The Key Factors
Metamorphism occurs when rocks are subjected to:
● High temperatures (150°C–1,000°C), often from nearby magma or Earth's internal heat.
● Intense pressure from overlying rock layers or tectonic plate collisions.
For example, shale, a sedimentary rock, becomes slate when compressed, while limestone transforms into marble under heat.
Types of Metamorphism
1. Regional Metamorphism: Covers large areas where tectonic forces squeeze rocks (e.g., forming gneiss from granite).
2. Contact Metamorphism: Occurs when rocks touch magma, "baking" them (e.g., creating hornfels near lava flows).
Visible Changes
Metamorphic rocks often develop:
● Foliation: Layers or bands from aligned minerals (seen in schist or slate).
● Crystalline textures: Interlocking mineral grains (like in quartzite or marble).
Why It Matters
These rocks reveal Earth's history, showing where mountains formed or continents collided. They’re also valuable resources—marble and slate are used in construction, while garnet-rich schist serves as abrasives.
Metamorphic rocks prove Earth’s crust is dynamic, constantly reshaping under powerful forces.
What is the main idea of this passage?
How volcanoes create igneous rocksThe process of sedimentary rock formationHow heat and pressure transform existing rocks into metamorphic rocksWhere to find valuable minerals in natureWhat is metamorphism?
The melting of rocks into magmaThe weathering of rocks at Earth's surfaceThe transformation of rocks while remaining solidThe compression of sediments into layersWhich factor does NOT contribute to metamorphism?
High temperatures (150°C-1,000°C)Exposure to wind and rainIntense pressure from tectonic platesHeat from nearby magmaWhat happens to shale during metamorphism?
It melts into lavaIt becomes slateIt turns into sandstoneIt forms graniteWhat is foliation?
The melting point of mineralsLayers or bands formed by aligned mineralsThe process of rock erosionCracks caused by earthquakesWhich type of metamorphism occurs over large areas?
Contact metamorphismRegional metamorphismSurface metamorphismVolcanic metamorphismWhat valuable resource comes from metamorphic rocks?
Coal for energyMarble for constructionOil for fuelSand for glassWhy are metamorphic rocks important to geologists?
They reveal Earth's history of mountain formationThey are the main source of fossilsThey form most of Earth's surfaceThey create new tectonic plates
