metamorphism

Imagine a rock buried deep within the Earth, slowly changed by heat and pressure. That is the heart of metamorphism. In geology, it describes the process in which an existing rock changes in mineral makeup, texture, or structure without melting into liquid. It is not just surface damage or weathering; it is an internal change that happens under strong conditions deep underground.

You can see the result in rocks like marble, which forms from limestone, or slate, which forms from shale. The word is mainly used in earth science, especially when talking about how rocks change deep below the surface.

Metamorphism is the geological process by which an existing rock is changed by heat, pressure, and sometimes chemically active fluids. The change happens while the rock remains solid, so it does not melt into magma. Instead, its minerals recrystallize, its texture shifts, and its internal structure can be rearranged.

This process can affect igneous, sedimentary, or even older metamorphic rocks. For example, shale can be changed into slate, limestone can turn into marble, and granite can become gneiss under the right conditions. These are not small outer changes. The rock is altered from within as minerals grow, align, or break down and new ones form.

Geologists often talk about different kinds of metamorphism depending on the cause. Contact metamorphism happens when rock is heated by nearby magma. Regional metamorphism happens over large areas during mountain building, where both heat and pressure are strong. In all cases, the idea is the same: an older rock is transformed into a new form in the solid state. The word is mostly technical and is used chiefly in geology.