Which type of the rock can be foliated?
A. Igneous rock that cools quickly.
B. Metamorphic rock
C. Sedimentary rock
D. Igneous rock that cools slowly
B. Metamorphic rock
The correct answer is B. Metamorphic rock.
The type of rock that can be foliated is B. Metamorphic rock.
To understand why metamorphic rock can be foliated, let's first understand what foliation means. Foliation refers to the arrangement of mineral grains within a rock, which creates parallel layers or bands. These layers are usually caused by the application of pressure and heat over time, which causes the minerals within the rock to realign and recrystallize, resulting in the formation of foliation.
Metamorphic rocks are formed from pre-existing rocks (igneous, sedimentary, or even other metamorphic rocks) that undergo significant changes due to heat, pressure, and chemical processes. These changes occur over a long period of time, often deep within the Earth's crust. As a result, the minerals in the rock can be reoriented, squeezed, and realigned in response to the intense pressure and temperature conditions.
This process of recrystallization and mineral reorientation is what gives metamorphic rocks their foliated texture. Some examples of foliated metamorphic rocks include gneiss, schist, and slate. These rocks exhibit distinct bands or layers that are visible to the naked eye and are formed due to the intense pressure and heat experienced during their formation.
In contrast, igneous rocks (both those that cool quickly and those that cool slowly) and sedimentary rocks generally do not exhibit foliation. Igneous rocks are formed from the cooling and solidification of molten magma or lava, and their texture is primarily determined by the rate of cooling, mineral composition, and the presence of gas bubbles. Sedimentary rocks are formed from the accumulation and lithification of sediments such as sand, clay, or organic matter, and their texture is mainly influenced by the type of sediment and the process of compaction and cementation.
Thus, only metamorphic rocks are capable of exhibiting foliation due to the geological processes they undergo.