Metamorphic rocks form when existing rocks undergo transformation due to intense heat, pressure, or chemical processes without melting completely. This metamorphism creates entirely new rock types with unique textures and mineral compositions.
Metamorphic Processes
Metamorphism occurs deep within the Earth's crust where temperatures range from 200°C to 700°C and pressures are many times greater than at the surface. These conditions cause minerals to recrystallize and reorganize, creating new textures and sometimes entirely new minerals.
Types of Metamorphism
Contact Metamorphism: Occurs when rocks are heated by nearby magma intrusions. The heat causes localized changes in the surrounding rock, creating a metamorphic aureole.
Regional Metamorphism: Results from large-scale geological processes such as mountain building, where vast areas of rock are subjected to increased temperature and pressure over long periods.
Dynamic Metamorphism: Occurs along fault zones where rocks are subjected to intense pressure and shearing forces, creating mylonites and other deformed rock types.
Common Metamorphic Rocks
Marble: Forms from limestone or dolomite through recrystallization of carbonate minerals. Prized for sculpture and architecture due to its workability and beauty.
Slate: Develops from shale through low-grade metamorphism, creating a fine-grained rock that splits easily along parallel planes. Traditionally used for roofing and writing tablets.
Gneiss: A high-grade metamorphic rock with distinctive banded appearance, formed from granite or other rocks under intense heat and pressure.
Metamorphic Grade
The intensity of metamorphism is classified into grades: low, medium, and high. Each grade produces characteristic mineral assemblages that help geologists understand the conditions under which the rock formed.
← Back to Rock Explorer