Which factor contributes to the formation of metamorphic rocks?

The formation of metamorphic rocks is primarily influenced by heat and pressure. Metamorphic rocks originate from pre-existing rocks, which can be either igneous, sedimentary, or other metamorphic rocks. These original rocks undergo significant changes in their mineral composition and structure under conditions of elevated temperature and pressure within the Earth's crust.

When rocks are subjected to these conditions, the minerals can recrystallize, creating new metamorphic minerals that are stable at those higher temperatures and pressures. Additionally, the arrangement of these minerals may change, resulting in foliation or other textures characteristic of metamorphic rocks. This process is typically called metamorphism and can lead to the formation of various types of metamorphic rocks, such as schist, gneiss, and marble.

The other factors listed—cooling of magma, weathering of sediment, and evaporation of water—are associated with different geological processes such as igneous rock formation, sedimentary rock formation, and the water cycle, respectively, and do not contribute to the metamorphic process.