What is metamorphism?

Metamorphism is the process by which existing rocks are transformed into new types of rocks through the application of heat and pressure over geological time. This transformation does not involve melting, as is the case in igneous rock formation, but rather changes the mineral structure and texture of the rock. During metamorphism, the original rock, known as the parent rock or protolith, can undergo alterations in its mineral composition and physical structure due to these intense conditions.

When rocks are subjected to heat, it can cause some minerals to become stable at elevated temperatures, while the application of pressure can lead to the reorientation of minerals, resulting in foliation or other forms of texture. This is why heat and pressure are critical components of metamorphism, defining it as the process that produces metamorphic rocks from pre-existing ones such as sedimentary, igneous, or other metamorphic rocks.

The other processes mentioned involve different geological mechanisms: heating sedimentary rocks into igneous rocks pertains to melting and solidification, weathering is the breakdown of rocks into smaller fragments without altering their chemical composition, and crystallizing magma refers specifically to the formation of igneous rocks from molten material.