Final answer:
During metamorphism, additional pressure is exerted on a rock due to the increase in temperature and intensity of pressure. Heat softens minerals in the rock, allowing for recrystallization, while pressure forces the minerals to reorient, resulting in foliation.
Step-by-step explanation:
Metamorphism occurs under subsolidus conditions, meaning there is no melting.
During metamorphism, additional pressure is exerted on a rock due to the increase in temperature and intensity of pressure. Metamorphic rocks are formed when pre-existing rocks are altered by heat and/or pressure.
The increase in pressure can occur during tectonic plate collisions or as a result of the weight of overlying rocks.
Heat works to "soften" minerals in the rock, allowing ions to migrate in and out of crystal structures. Then, pressure forces the minerals to reorient.
This process, known as foliation, is the most noticeable feature when recognizing metamorphic rocks.
It is important to note that metamorphism occurs under subsolidus conditions, meaning that elevated temperatures are not high enough to cause melting. Instead, the minerals in the rock undergo recrystallization without melting.