What is a known effect of metamorphism on rocks?

Metamorphism is the process by which existing rocks undergo a transformation due to changes in temperature, pressure, and the presence of chemically active fluids. One significant effect of this process is the formation of larger crystals in the rocks.

When rocks are subjected to high pressures and temperatures over time, the minerals within them can recrystallize, allowing for the growth of larger mineral crystals. This is particularly evident in metamorphic rocks such as gneiss and schist, where foliation and the alignment of minerals often result in the emergence of larger crystals compared to their protolith (the original rock). This change is driven by the migration and rearrangement of mineral components, which can lead to improved crystal structure, size, and overall texture of the metamorphic rock.

Other options suggest effects that do not align with the typical outcomes of metamorphism. For instance, decreased density and increased porosity are generally not characteristic of this process. Instead, metamorphic rocks tend to become denser due to the recrystallization of minerals. Granulation into fine particles describes a process more related to weathering and erosion, rather than the solid-state changes that occur during metamorphism. Thus, the formation of larger crystals is a recognized hallmark of metamorphic processes.