What type of rock is formed by pre-existing rocks undergoing metamorphism?

Metamorphic rocks are formed from pre-existing rocks, which can be either igneous, sedimentary, or other metamorphic rocks. This transformation occurs under conditions of high pressure, high temperature, or chemically active fluids, leading to significant changes in the mineral composition and structure of the original rock. During this process, mineral grains may grow larger, new minerals may form, and the overall texture and appearance of the rock can change dramatically.

Examples of metamorphic rocks include schist, gneiss, and quartzite, all of which illustrate how the original rock types can be transformed through metamorphic processes. This fundamental concept distinguishes metamorphic rocks from igneous, sedimentary, and volcanic rocks, which are formed through different geological processes such as the cooling of magma or the accumulation of sediments.