The three main types of rocks are igneous, sedimentary, and metamorphic, each formed through distinct processes:
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Igneous Rocks: These rocks are formed from the cooling and solidification of molten material known as magma (beneath the surface) or lava (on the surface). There are two primary types of igneous rocks:
- Intrusive Igneous Rocks: Formed from magma that cools slowly beneath the Earth's surface, allowing large crystals to form (e.g., granite).
- Extrusive Igneous Rocks: Formed from lava that cools quickly on the Earth's surface, resulting in smaller crystals (e.g., basalt).
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Sedimentary Rocks: These rocks are formed through the accumulation and consolidation of sediments, which can include mineral particles, organic matter, and the remains of plants and animals. The formation process generally involves:
- Weathering and Erosion: Breaking down existing rocks into smaller particles.
- Deposition: Accumulating these particles in layers, often in bodies of water.
- Lithification: The compaction and cementation of these sediments into solid rock (e.g., sandstone, limestone).
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Metamorphic Rocks: These rocks are formed when existing rocks (igneous, sedimentary, or other metamorphic rocks) undergo a transformation due to high temperature, high pressure, or chemically active fluids, usually deep within the Earth. This process is known as metamorphism and can result in:
- Foliated Metamorphic Rocks: Characterized by a layered or banded appearance due to the alignment of minerals (e.g., schist, gneiss).
- Non-foliated Metamorphic Rocks: Lacking a banded appearance, often formed from a single mineral (e.g., marble, quartzite).
These three rock types and their formation processes illustrate the rock cycle, which describes the continuous transformation of rocks through various geological processes.