Difference Between Mafic and Felsic

Mafic and felsic are not commonly used terms, as one may observe. The few that know the existence of these words are mainly geologists or ones related to that field of study. So, what is it?

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Igneous rocks on chemical analysis were found to be abundant in silicate oxides and therefore it was decided that these igneous rocks would be differentiated based on their silica content.

Mafic and felsic are the terms used to describe the silica content of igneous rocks formed on the cooling of lava. Sometimes, they are also used to differentiate the characteristics of the lava (or magma).

Mafic vs Felsic

The difference between Mafic and Felsic rocks are the silica content present. Since igneous rocks are characterised by silica content in them, mafic is the one with less silica content (approx. 45-55%) while felsic is the one with a greater silica content (approx.70-90%).

Mafic vs Felsic

There is a contrasting difference even in the appearance of the two igneous rocks; one being dark shaded and the other having light shade.


 

Comparison Table

Parameters of ComparisonMaficFelsic
Viscosity of LavaLow viscosity due to the high temperature of lavaHigh viscosity
DensityHigh density and heavyLow density and lightweight
ColourDark shades of green, or blackLight-coloured
Mineral ContentRich in magnesium and ironRich in aluminium and silica
Silica Level45-55%70-85%

 

What is Mafic?

Mafic is the acronym for magnesium and ferric (Latin for Iron) because this igneous rock is rich in these two minerals. The mafic lava is usually at 950 and often leads to a weak volcanic eruption.

Mafic rocks are generally found in dark shades of green or greenish-black in colour. Their characteristics are medium to coarse-grained. 

The low density of these rocks is due to the low content of silica present in them. This is since their origin is mostly the sea bed, that is not abundant in silica.

Due to the low viscosity of the lava, the lava erupted are usually very runny. Basalt is a well-known example of a mafic rock.

mafic
 

What is Felsic?

Felsic is the term used for the rocks rich in the mental feldspar, that contains aluminium and silica at high levels. The felsic lava is usually found at 650-750˚ C and is can cause explosive volcanic eruptions.

The high silica content (70-85%) is because of the geographical location the felsic rocks are found at. They are mostly found in specific geographic areas known as convergent zones, where the geologic plates collide.

Graphite is a well-known example of felsic rocks.

felsic

Main Differences Between Mafic and Felsic

  1. Felsic is also rich in low-density minerals like oxygen, sodium and potassium. Thus, these rocks have low density unlike mafic rock, which have high density are heavy.
  2. The minerals present in the two is also the reason due to which there is a contrasting difference in their characteristic appearance.

References

  1. https://www.sciencedirect.com/science/article/pii/S0024493704002014
  2. https://mingtang.me/publications/Tang%20et%20al_Science%202016.pdf
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