Felsic

Definition

Felsic refers to a composition of igneous rocks that is rich in silica and light-colored minerals, primarily feldspar and quartz. This term indicates a specific mineral content that influences the physical properties, color, and behavior of the resulting rock. Felsic rocks typically form from the slow crystallization of magma beneath the Earth's surface, leading to a range of rock types including granite and rhyolite.

5 Must Know Facts For Your Next Test

1. Felsic rocks typically have over 65% silica content, which gives them a lighter color compared to mafic rocks.
2. Common examples of felsic rocks include granite and rhyolite, both of which are formed from different cooling rates of magma.
3. Felsic minerals, like quartz and feldspar, crystallize at lower temperatures than mafic minerals, influencing the cooling history of the rock.
4. The formation of felsic rocks is often associated with continental crust processes, where magma rises slowly allowing for crystal growth.
5. Felsic magmas tend to be more viscous than mafic magmas due to their higher silica content, affecting volcanic eruptions when these rocks are formed.

Review Questions

• How does the composition of felsic rocks compare to that of mafic rocks in terms of mineral content and physical properties?
  • Felsic rocks contain high amounts of silica and are primarily composed of light-colored minerals like quartz and feldspar. In contrast, mafic rocks have lower silica content and are rich in dark minerals such as pyroxene and olivine. This difference in composition not only affects the color—felsic rocks are generally lighter—but also their physical properties, as felsic magmas tend to be more viscous compared to the fluidity seen in mafic magmas.
• What role does temperature play in the crystallization process of felsic magmas, and how does this affect the resulting rock types?
  • Temperature plays a critical role in the crystallization of felsic magmas because felsic minerals crystallize at lower temperatures than their mafic counterparts. This leads to slower cooling rates when magma is trapped beneath the Earth's surface, resulting in coarse-grained textures found in rocks like granite. Conversely, if the magma erupts quickly onto the surface, it can cool rapidly and form fine-grained rocks like rhyolite, illustrating how temperature affects not only mineral composition but also texture.
• Evaluate the significance of felsic rock formation processes within the context of continental crust development and volcanic activity.
  • Felsic rock formation is vital for understanding continental crust development because these rocks are predominant in continental settings due to their high silica content. The slow crystallization processes associated with felsic magmas contribute to the stability and growth of continental crust over geological time scales. Furthermore, when these felsic magmas erupt violently due to their high viscosity, they can lead to explosive volcanic events, shaping landscapes and impacting ecosystems significantly. This interplay between felsic rock formation and volcanic activity highlights their importance in geological processes.

Related terms

Mafic: Mafic describes igneous rocks that are rich in magnesium and iron, usually darker in color compared to felsic rocks.

Silica: Silica is a chemical compound composed of silicon and oxygen, which is a major component in many minerals found in felsic rocks.

Granite: Granite is a common felsic intrusive igneous rock known for its coarse-grained texture and is primarily composed of quartz, feldspar, and mica.