Mafic

Definition

Mafic refers to a type of igneous rock that is rich in magnesium and iron, characterized by a darker color and higher density compared to felsic rocks. Mafic rocks are primarily found in the Earth's mantle and oceanic crust, and they play a significant role in understanding the planet's composition and internal structure.

5 Must Know Facts For Your Next Test

1. Mafic rocks typically have a lower silica content, usually ranging from 45% to 52%, which contributes to their darker color and denser composition.
2. Common mafic rocks include basalt and gabbro, with basalt being extrusive and gabbro being intrusive in nature.
3. Mafic magma tends to be less viscous than felsic magma, allowing it to flow more easily during volcanic eruptions.
4. Mafic minerals such as olivine, pyroxene, and amphibole are prevalent in these rocks, contributing to their high melting points.
5. The formation of mafic rocks is often associated with divergent tectonic boundaries, where magma rises from the mantle to create new oceanic crust.

Review Questions

• How do mafic rocks differ from felsic rocks in terms of composition and properties?
  • Mafic rocks are rich in magnesium and iron, resulting in a darker color and higher density than felsic rocks, which are rich in silica and lighter-colored minerals. The silica content in mafic rocks generally ranges from 45% to 52%, while felsic rocks contain over 65% silica. This difference in composition influences the physical properties of the rocks, such as their melting points and viscosity when forming magma.
• Discuss the role of mafic rocks in understanding the Earth's structure and how they relate to the composition of oceanic crust.
  • Mafic rocks play a critical role in understanding the Earth's structure because they constitute a significant part of the oceanic crust, primarily composed of basalt. This knowledge helps geologists infer details about tectonic processes and the dynamics of the mantle. The presence of mafic material suggests that oceanic crust is formed through volcanic activity at mid-ocean ridges, providing insights into plate tectonics and seafloor spreading.
• Evaluate how the characteristics of mafic magma influence volcanic eruptions compared to felsic magma.
  • Mafic magma is generally less viscous than felsic magma due to its lower silica content, allowing it to flow more freely. This property results in less explosive volcanic eruptions for mafic materials, which often lead to gentle lava flows. In contrast, felsic magma's higher viscosity can trap gases, leading to more explosive eruptions. Understanding these differences helps scientists predict volcanic activity and assess potential hazards associated with different types of eruptions.

Related terms

Felsic: A category of igneous rocks that are rich in silica and light-colored minerals like quartz and feldspar, contrasting with mafic rocks.

Basalt:

A common type of mafic rock that forms from the rapid cooling of lava at the Earth's surface, typically found in oceanic crust.

Gabbro: An intrusive mafic rock that crystallizes slowly beneath the Earth's surface, having a coarse-grained texture.