The correct option is
C. Igneous Rock.
Detailed Explanation
- Definition of Igneous Rock:
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Igneous rocks are formed from the cooling and solidification of molten rock material known as magma (when it is beneath the Earth's surface) or lava (when it erupts onto the surface). This process can occur either slowly, allowing large crystals to form, or quickly, resulting in smaller crystals.
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Formation Process:
- Magma: When magma cools slowly beneath the Earth's surface, it forms intrusive igneous rocks (also known as plutonic rocks). An example of this is granite, which has large crystals due to the slow cooling process.
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Lava: When lava cools quickly after a volcanic eruption, it forms extrusive igneous rocks (also known as volcanic rocks). An example of this is basalt, which has small crystals because of the rapid cooling.
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Key Characteristics:
- Igneous rocks are characterized by their crystalline structure, which is a direct result of the cooling process. The mineral composition can vary widely, leading to different types of igneous rocks.
Why Other Options Are Incorrect
- A. Sedimentary Rock:
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Sedimentary rocks are formed from the accumulation and compaction of mineral and organic particles, or through the precipitation of minerals from water. They do not form from the cooling of magma or lava. Examples include sandstone and limestone.
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B. Metamorphic Rock:
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Metamorphic rocks are formed from existing rocks (either igneous, sedimentary, or other metamorphic rocks) that have been transformed by heat, pressure, or chemically active fluids. This process is known as metamorphism. They do not originate from the cooling of magma or lava. Examples include schist and marble.
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D. Organic Rock:
- Organic rocks are a subset of sedimentary rocks that are formed from the accumulation of plant or animal debris. They are not formed from the cooling of magma or lava. An example is coal, which is formed from decomposed plant material.
Summary of Key Points
- Igneous rocks are formed from the cooling and solidification of magma or lava.
- They can be classified into intrusive (formed from magma) and extrusive (formed from lava) types.
- Sedimentary and metamorphic rocks are formed through different processes and do not involve the cooling of molten rock.
- Understanding the rock cycle is essential for recognizing how different types of rocks are formed and transformed over geological time.
Revision Summary
- Igneous rocks form from the cooling of magma or lava.
- Intrusive igneous rocks cool slowly underground; extrusive igneous rocks cool quickly on the surface.
- Sedimentary rocks form from particle accumulation; metamorphic rocks form from existing rocks under heat and pressure.
- Recognizing the differences in rock formation processes is crucial for understanding geology.