1. Foliation: This is the most defining characteristic of metamorphic rocks. It refers to the parallel alignment of mineral grains within the rock, creating a layered or banded appearance. This occurs due to directed pressure during metamorphism, causing minerals to recrystallize and align themselves perpendicular to the stress.
2. Recrystallization: Metamorphic rocks often display larger mineral grains than their parent rocks. This is because the heat and pressure during metamorphism cause existing minerals to dissolve and recrystallize into larger, more stable forms. This process results in increased density and hardness in the rock.
3. Distinctive Mineral Assemblages: Metamorphic rocks often contain specific minerals that are not found in their original sedimentary or igneous counterparts. These minerals, such as garnet, kyanite, or staurolite, are formed under specific temperature and pressure conditions present during metamorphism.
1. No Foliation: Sedimentary rocks form from the accumulation and cementation of sediments. Since there is no directed pressure, the grains remain randomly arranged, lacking the layered structure of metamorphic rocks.
2. Limited Recrystallization: While some recrystallization might occur during the cementation process, it is nowhere near the extent seen in metamorphic rocks. The lack of high heat and pressure prevents extensive mineral transformations.
3. Different Mineral Assemblages: Sedimentary rocks typically contain minerals that are stable at the Earth's surface, reflecting their formation from weathered and eroded materials. They lack the unique mineral assemblages indicative of the high temperatures and pressures characteristic of metamorphism.
