The correct option is
C. Sedimentary.
Detailed Explanation
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Definition of Sedimentary Rocks:
Sedimentary rocks are formed through a process that involves the accumulation, compaction, and cementation of sediment particles over time. These sediments can originate from various sources, including the weathering and erosion of pre-existing rocks, the remains of plants and animals, and chemical precipitation from water.
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Formation Process:
- Accumulation: Sediments, which can be small particles like sand, silt, and clay, or larger fragments, settle in layers in various environments such as riverbeds, lakes, and oceans.
- Compaction: Over time, as more layers of sediment accumulate on top, the weight of the overlying material compresses the deeper layers, reducing their volume and expelling water.
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Cementation: Minerals dissolved in water can precipitate and fill the spaces between sediment particles, binding them together to form solid rock.
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Examples of Sedimentary Rocks:
Common examples include sandstone (formed from sand), limestone (often formed from the accumulation of shell fragments), and shale (formed from clay particles).
Why Other Options Are Incorrect
- A. Igneous:
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Igneous rocks are formed from the solidification of molten rock material (magma or lava). They do not involve the accumulation of sediments. Instead, they can be classified into two types: intrusive (formed beneath the Earth's surface) and extrusive (formed on the surface).
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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, known as metamorphism, alters the mineral composition and structure of the original rock but does not involve sediment accumulation.
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D. Volcanic:
- The term "volcanic" typically refers to igneous rocks that are formed from lava that cools and solidifies on the Earth's surface. Like igneous rocks, volcanic rocks do not form from sediment accumulation.
Summary of Key Points
- Sedimentary rocks are formed from the accumulation, compaction, and cementation of sediments over time.
- They can originate from weathered materials, biological remains, or chemical processes.
- Igneous and metamorphic rocks are formed through different processes (solidification of magma and transformation under heat/pressure, respectively).
- Volcanic refers to a type of igneous rock formed from lava.
Revision Summary
- Sedimentary rocks form from the accumulation and compaction of sediments.
- They are classified based on their origin: clastic, chemical, and organic.
- Igneous rocks form from molten material, while metamorphic rocks result from changes in existing rocks.
- Understanding the rock cycle is crucial for recognizing how different rock types are interrelated.