What is the alteration of the composition or structure of a rock due to heat and pressure called?

The alteration of the composition or structure of a rock due to heat and pressure is called metamorphism. This process involves significant changes in the mineralogy and texture of the rock, often resulting in the formation of metamorphic rocks such as schist, gneiss, or marble. Metamorphism typically occurs deep within the Earth's crust, where rocks are subjected to high temperatures and pressures over long periods. This transformation can occur without the rock melting, which distinguishes it from igneous processes.

In contrast, compacting refers to the process of densifying sediment by applying pressure over time, usually in the context of sedimentary rock formation. Weathering involves the breaking down and alteration of rocks at the Earth's surface due to environmental factors like water, wind, and temperature changes. Sedimentation describes the process by which sediments are deposited, often leading to the formation of sedimentary rocks, but does not involve the transformative effects of heat and pressure that characterize metamorphism.