The continental crust is primarily composed of various types of rocks and minerals, with a significant amount of diversity in its composition. Here are the main features of the continental crust's composition:
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Rocks: The continental crust mainly consists of igneous, metamorphic, and sedimentary rocks.
- Igneous rocks: These include granite and other felsic rocks, which are rich in silica and aluminum. Granitic rocks are prevalent because they form from the slow crystallization of magma beneath the Earth's surface.
- Metamorphic rocks: Common examples include gneiss, schist, and marble. These rocks form from the alteration of existing rocks under heat and pressure.
- Sedimentary rocks: These consist of sandstones, shales, and limestones, forming from the accumulation and compaction of sediments.
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Minerals: The traditional minerals found in the continental crust include:
- Feldspar: A major component, often found in both igneous and metamorphic rocks.
- Quartz: Abundant in many rock types and particularly in granite and sandstones.
- Mica: Commonly found in metamorphic rocks and granites.
- Amphibole: Found in many igneous and metamorphic rocks.
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Chemical Composition: The continental crust has a higher silica (SiO2) content compared to the oceanic crust, averaging around 55% to 70% by weight. Other significant elements include:
- Aluminum (Al)
- Iron (Fe)
- Calcium (Ca)
- Sodium (Na)
- Potassium (K)
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Density and Thickness: The continental crust is generally less dense than the oceanic crust, with an average density of about 2.7 grams per cubic centimeter. Its thickness varies, averaging around 30-40 kilometers, but can be even thicker in some mountain ranges.
Overall, the continental crust is a complex and varied layer of the Earth, rich in lighter elements and composed of a wide range of rock types and minerals.