MCQ
Q.
Marble is an example of which type of rock?
Correct Answer: C
- A rock is any naturally occurring solid mass or aggregate of one or more minerals or mineraloid matter.
- The earth's crust is composed of rocks.
- It is categorized by the minerals included its chemical composition and the way in which it is formed.
- The rock cycle is a basic concept of transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous.
- Each rock type is altered when it is forced out of its equilibrium conditions.
Metamorphic Rocks
- The word metamorphic means ‘change of form’.
- These rocks form under the action of pressure, volume and temperature (PVT) change.
- Metamorphism occurs when rocks are forced down to lower levels by tectonic processes.
- Or when molten magma rising through the crust comes in contact with the crustal rocks.
- Or the underlying rocks are subjected to great amounts of pressure by overlying rocks.
- Metamorphism is a process by which already consolidated rocks undergo recrystallisation and reorganisation of materials within original rocks.
- Common metamorphic rocks include slate, schist, gneiss, and marble.
Thus, marble is an example of metamorphic rock.
Igneous Rocks:
- Igneous Rocks are formed by crystallization from a liquid or magma.
- They are also known as primary rocks.
- There are two types of Igneous rocks based on their mode of occurrence:
- Volcanic or extrusive igneous rocks that form when the magma cools and crystallizes on the surface of the Earth
- Intrusive or plutonic igneous rocks wherein the magma crystallizes at depth in the Earth.
- Magma is a mixture of liquid rock, crystals, and gas with a wide range of chemical compositions, temperature, and properties of a liquid.
Sedimentary Rocks:
- The word ‘sedimentary’ is derived from the Latin word sedimentum, which means settling.
- Sedimentary rocks are called secondary rocks.
- They are often the result of the accumulation of small pieces broken off of pre-existing rocks.
- In many sedimentary rocks, the layers of deposits retain their characteristics even after deposition.
- Hence, we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale etc.
