Mafic Vs. Felsic: Comprehensive Comparison

Felsic and mafic rocks are two main types of igneous rocks, which are rocks that are formed from the cooling and solidification of magma or lava. Felsic rocks are high in silica (SiO2), while mafic rocks are low in silica. This difference in silica content gives the two types of rocks different physical and chemical properties.

Mafic is a term used to describe silicate minerals, magma, and igneous rocks which are rich in magnesium and iron. The term  Mafic comes from "magnesium" and "ferric" (iron).

Felsic is a term used to describe silicate minerals, magma, and igneous rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. The term "felsic" comes from the words "feldspar" and "silica,".

 

Difference Between Mafic and Felsic
Mafic Vs. Felsic Rocks: The Difference Between Mafic and Felsic

Felsic

  • Felsic: Derived from "feldspar" and "silica," felsic rocks are rich in silica and aluminum. They contain a higher proportion of light-colored minerals like quartz, feldspar (both plagioclase and orthoclase), and muscovite.
  • Felsic rocks are typically light in color, such as white, pink, or gray. They are also relatively low in density and have high melting points.
  • Silica Content: Higher silica content, typically above 65%.
  • Color: Light-colored (white, light gray, pink).
  • Density: Lower density because of the higher silica content and lighter minerals.
  • Viscosity: Higher viscosity due to higher silica content, which makes felsic magma more viscous and sticky.
  • Melting Temperature: Lower melting temperatures, around 650-800°C.
  • Plate Tectonic Setting: Commonly found at convergent plate boundaries, especially in continental crust regions where subduction and melting of the crust occur.
  • Mineral Content: High in minerals such as quartz, potassium feldspar (orthoclase), and sodium-rich plagioclase feldspar.
  • Volcanic Activity: Produces more explosive volcanic eruptions due to higher viscosity of the magma. Pyroclastic flows and explosive activity are more common.
  • Examples of Felsic Volcanoes: Stratovolcanoes (e.g., Mount St. Helens in Washington, USA).

Mafic

  • Mafic: Derived from "magnesium" and "ferric" (iron), mafic rocks are rich in magnesium and iron.
  • Mafic rocks, on the other hand, are typically dark in color, such as black or green. They are also relatively dense and have low melting points. 
  • Silica Content: Lower silica content, typically between 45-55%.
  • Color: Dark-colored (black, dark green, dark gray).
  • Density: Higher density due to the presence of heavier elements like iron and magnesium.
  • Viscosity: Lower viscosity due to lower silica content, which makes mafic magma less viscous and more fluid.
  • Plate Tectonic Setting: Commonly found at divergent plate boundaries (mid-ocean ridges) and hotspots, where partial melting of the mantle occurs. They are also the main component of the Earth's mantle.
  • Volcanic Activity: Produces less explosive volcanic eruptions due to lower viscosity of the magma. Lava flows are more common.
  • Examples of Mafic Volcanoes: Shield volcanoes (e.g., Mauna Loa in Hawaii).
  • Mineral Content: Mafic rocks are composed of minerals such as olivine, pyroxene, and amphibole.

 

Mafic and Felsic rocks
Mafic and Felsic Rocks

Formation of Felsic and Mafic Rocks

Felsic rocks are formed from the cooling and crystallization of felsic magma, which is relatively rich in the lighter elements silicon, oxygen, aluminum, sodium, and potassium. Felsic magma is less dense and more viscous than mafic magma, so it rises more slowly through the Earth's crust. When it reaches the surface, it can either cool and crystallize into extrusive felsic rocks like rhyolite and obsidian, or it can intrude into the surrounding rock and cool slowly to form intrusive felsic rocks like granite and pegmatite.

Mafic rocks are formed from the cooling and crystallization of mafic magma, which is relatively rich in the heavier elements magnesium and iron. Mafic magma is more dense and less viscous than felsic magma, so it rises more quickly through the Earth's crust. When it reaches the surface, it can either cool and crystallize into extrusive mafic rocks like basalt and scoria, or it can intrude into the surrounding rock and cool slowly to form intrusive mafic rocks like gabbro and dolerite.

Mineral Composition of Mafic and Felsic Rocks

Mafic rocks are dark in color and have a high density. They are typically composed of the following minerals:

  • Olivine
  • Pyroxene
  • Amphibole
  • Mica
  • Plagioclase feldspar
Felsic rocks are light in color and have a low density. They are typically composed of the following minerals:
  • Quartz
  • K-feldspar
  • Plagioclase feldspar
  • Mica
Classification diagram for igneous rocks
Classification diagram for igneous rocks

Examples of Felsic and Mafic Rocks

Examples of felsic rocks include

Examples of mafic rocks include

  • Basalt
  • Gabbro
  • Diabase
  • Peridotite
  • Scoria

Felsic and mafic rocks are two important types of igneous rocks. Their different physical and chemical properties are due to their different silica contents. Felsic rocks are high in silica, while mafic rocks are low in silica.

See also:
General Classification of Igneous Rocks
How to Classify Igneous Rocks Into (Ultramafic, Mafic, Intermediate and Felsic)?

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