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 often contain fossils and are typically layered. Examples include sandstone and limestone. Since they do not form from magma or lava, this option is incorrect.
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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. Examples include schist and marble. Since they do not originate from the cooling of magma or lava, this option is also incorrect.
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D. Fossil Rock:
- The term "fossil rock" is not a standard geological classification. It may refer to sedimentary rocks that contain fossils, but it does not represent a distinct type of rock formed from magma or lava. Therefore, this option is not valid in the context of the question.
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 rocks form from particle accumulation, while metamorphic rocks arise from the transformation of existing rocks.
- The term "fossil rock" is not a recognized geological category.
Revision Summary
- Igneous rocks are formed 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 particles and organic material, while metamorphic rocks result from the alteration of existing rocks.
- "Fossil rock" is not a standard geological term and does not apply to the formation process of igneous rocks.