The correct option is
C. Igneous.
Detailed Explanation
- Definition of Igneous Rock:
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Igneous rocks are formed from the cooling and solidification of molten 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 Formation: Deep within the Earth, high temperatures and pressures cause rocks to melt, forming magma.
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Cooling and Solidification: When magma rises to the surface and erupts as lava, it cools rapidly, forming volcanic (extrusive) igneous rocks like basalt. If magma cools slowly beneath the surface, it forms intrusive igneous rocks like granite, which have larger crystals due to the extended cooling time.
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Types of Igneous Rocks:
- Intrusive Igneous Rocks: Formed from magma that cools slowly underground. Examples include granite and diorite.
- Extrusive Igneous Rocks: Formed from lava that cools quickly on the Earth's surface. Examples include basalt and pumice.
Why Other Options Are Incorrect
- A. Sedimentary:
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Sedimentary rocks are formed from the accumulation and compaction of mineral and organic particles, or from the precipitation of minerals from water. They do not form from molten material. Examples include sandstone, limestone, and shale.
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B. Metamorphic:
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Metamorphic rocks are formed from existing rocks (either igneous, sedimentary, or other metamorphic rocks) that undergo a transformation due to high pressure, high temperature, or chemically active fluids. This process does not involve the cooling of molten material. Examples include schist, gneiss, and marble.
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D. Organic:
- Organic rocks are a subset of sedimentary rocks that are formed from the accumulation of plant or animal debris. They are not formed from molten material. 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 molten material (magma/lava).
- They can be classified into intrusive (cooling below the surface) and extrusive (cooling above the surface).
- Sedimentary and metamorphic rocks are formed through different processes and do not involve molten material.
- Organic rocks are a type of sedimentary rock formed from biological materials, not molten rock.
Revision Summary
- Igneous rocks form from the cooling of molten material (magma/lava).
- They are classified as intrusive (slow cooling) or extrusive (rapid cooling).
- Sedimentary rocks form from particle accumulation, while metamorphic rocks arise from existing rocks under heat and pressure.
- Organic rocks are a type of sedimentary rock formed from biological debris.