What process leads to the formation of metamorphic rocks?

Metamorphic rocks form through the process of heat and pressure acting on existing rocks, which can be either igneous, sedimentary, or even older metamorphic rocks. This transformation occurs deep within the Earth’s crust where temperatures and pressures are significantly higher than at the surface.

During metamorphism, the mineral composition and structure of the rock are altered without the rock actually melting. This can lead to changes in texture, the formation of new minerals, and an increase in mineral alignment due to the directional pressure. For example, common metamorphic rocks such as schist and gneiss exhibit foliation, which is a layered appearance resulting from the alignment of minerals under directional stress.

In contrast, the other processes listed describe the formation of different types of rocks. The cooling and solidification of magma leads to igneous rocks, while the weathering and erosion of sediments results in sedimentary rocks. Biological activity refers to the role of organisms in altering the environment, which may contribute to sediment formation rather than directly creating metamorphic rocks. Thus, the correct understanding is that heat and pressure on existing rocks is what specifically leads to the formation of metamorphic rocks.