Felsic

Definition

Felsic refers to a category of igneous rocks and magmas that are rich in silica and light-colored minerals such as quartz and feldspar. This composition significantly influences the characteristics of Earth's crust, the formation of magma, and the classification of igneous rocks based on their mineral content and texture. Felsic materials are typically associated with continental crust and can lead to explosive volcanic eruptions due to their high viscosity.

5 Must Know Facts For Your Next Test

1. Felsic rocks typically contain over 65% silica, making them significantly lighter than mafic rocks.
2. Common examples of felsic rocks include granite and rhyolite, which are often found in continental regions.
3. Felsic magmas have higher viscosity due to their silica content, leading to slower movement and potential buildup of pressure within volcanic systems.
4. The light color of felsic rocks comes from the presence of minerals like quartz, orthoclase, and plagioclase feldspar.
5. Felsic volcanic eruptions are often more explosive compared to mafic eruptions because the high viscosity of felsic magma traps gases until pressure is released.

Review Questions

• How does the composition of felsic magmas affect volcanic activity compared to mafic magmas?
  • Felsic magmas have a higher silica content compared to mafic magmas, resulting in greater viscosity. This increased viscosity leads to a slower flow of magma, which can trap gases within it. As pressure builds up from the trapped gases, felsic eruptions tend to be more explosive when the magma finally escapes, contrasting with the more effusive eruptions typically associated with mafic magmas.
• Discuss the role of felsic rocks in shaping the Earth's crust and their distribution in continental regions.
  • Felsic rocks play a significant role in shaping the Earth's crust, particularly in continental regions where they are prevalent. Their composition typically results in lighter-colored granitic formations that contribute to mountain building processes. The presence of felsic materials also indicates past volcanic activity, as they are formed from cooling and solidification of high-silica magma. This distribution helps geologists understand tectonic processes and the geological history of an area.
• Evaluate the environmental implications of explosive volcanic eruptions associated with felsic magma on local ecosystems and climate.
  • Explosive eruptions linked to felsic magma can have profound environmental implications. The release of ash and gases can blanket large areas, impacting local ecosystems by burying vegetation and altering habitats. Moreover, the injection of volcanic ash into the atmosphere can lead to climate changes, such as temporary cooling due to reduced sunlight reaching the Earth's surface. These events can disrupt weather patterns, affect agricultural productivity, and challenge the resilience of ecosystems.

Related terms

Mafic: Mafic describes igneous rocks and magmas that are low in silica and rich in magnesium and iron, resulting in darker colors compared to felsic rocks.

Silica: Silica is a chemical compound (SiO2) that is a fundamental component of felsic rocks, influencing their properties, including viscosity and melting temperature.

Viscosity: Viscosity is a measure of a fluid's resistance to flow; felsic magma has high viscosity, which can trap gases and contribute to explosive volcanic activity.