What is the process by which rocks change due to temperature, pressure, and stress?

The process by which rocks change due to temperature, pressure, and stress is known as metamorphism. This occurs when existing rocks, whether they are igneous, sedimentary, or even older metamorphic rocks, are subjected to conditions that alter their mineral composition, texture, and structure without melting them.

During metamorphism, the high temperatures and pressures can cause minerals to recrystallize, resulting in the formation of new minerals that are stable under the new conditions. Additionally, the alignment of mineral grains may change due to directed stress, leading to the development of foliation or banding in the rock. This transformation can produce a wide variety of metamorphic rocks, such as schist, gneiss, or slate, each exhibiting distinct characteristics based on the original rock and the metamorphic conditions it experienced.

The other processes mentioned—melting, weathering, and sedimentation—represent different geological actions: melting refers to the process that turns solid rock into magma, weathering involves the breakdown and alteration of rocks at the Earth's surface, and sedimentation is the process where particles settle out of a fluid and accumulate to form sedimentary rocks. Each of these processes affects rocks in different ways and under different conditions compared to metamorphism.