Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What processes lead to the formation of metamorphic rocks?

1. Cooling of magma under the surface

2. Layering and compression of particles

3. High temperatures and pressures altering original rocks

4. Evaporation of mineral solutions

The correct answer is: High temperatures and pressures altering original rocks

The formation of metamorphic rocks primarily occurs through the processes of high temperatures and pressures that alter original rocks. This process, known as metamorphism, transforms pre-existing rocks—either igneous, sedimentary, or other metamorphic rocks—into metamorphic varieties. Under extreme conditions of temperature and pressure, the minerals within the original rock can change both chemically and physically. This often leads to re-crystallization of minerals, foliation (layering), and the development of new mineral assemblages that are stable under the new conditions. This transformation occurs deep within the Earth, where temperatures can rise above 200 degrees Celsius, and pressures can exceed thousands of atmospheres. As a result, the original texture and composition of the rock are significantly altered, resulting in a metamorphic structure that is distinctly different from its parent rock. Understanding these processes is crucial in geology because it helps differentiate metamorphic rocks from igneous and sedimentary types, which form through precipitation or cooling and solidification processes, rather than the direct alteration of existing materials.