Final answer:
A rock formed by the alteration of pre-existing rock through heat, pressure, and/or chemically reactive fluids is called a 3) metamorphic rock, which undergoes recrystallization to become more stable under new environmental conditions.
Step-by-step explanation:
A rock that is formed by the alteration of pre-existing rock through the processes of heat, pressure, and/or chemically reactive fluids is known as a 3) metamorphic rock. The term metamorphism indicates a change in form, where pre-existing rocks—whether they are igneous or sedimentary—are altered without melting into a new, more stable rock form. When exposed to such environmental changes, the rock undergoes recrystallization, meaning that its minerals change size, shape, or composition.
Metamorphic rocks can have a variety of appearances based on their protolith (the original rock before alteration) and the specific conditions and agents of metamorphism involved. At times, these rocks show a prominent feature called foliation, which refers to the orientation of the mineral grains within the rock that often occurs due to pressure. This contrast is what distinguishes metamorphic rocks from other rock types like igneous rocks, which cool from magma or lava, and sedimentary rocks, which form from cemented together sediment or mineral deposits.