Final answer:
Metamorphic rocks are formed by the phenomena of heat, pressure, and sometimes the presence of chemically reactive fluids, to recrystallize and change the mineral composition and texture of pre-existing igneous, sedimentary, or even other metamorphic rocks known as the protolith.
Step-by-step explanation:
The phenomena that cause the change from a parent rock to a metamorphic rock are primarily the effects of heat and pressure. During metamorphism, alterations occur due to the recrystallization of minerals when exposed to new conditions beneath the Earth's surface. These changes in temperature and pressure can also be accompanied by chemically reactive fluids that further drive the metamorphic process.
Foliation is one of the distinctive features that form due to mineral orientation under pressure during metamorphism. However, not all metamorphic rocks are foliated; those that do not show foliation are termed non-foliated or massive and often resemble igneous rocks in appearance.
The type of metamorphic rock that ultimately forms is dependent on the original protolith or parent rock and the specific conditions of temperature, pressure, and chemical environment to which it was subjected. Consequently, metamorphism completes the natural components of the rock cycle, transforming igneous or sedimentary rocks into metamorphic variations.