Difference Between Mafic and Felsic

Mafic vs Felsic

Mafic and Felsic are not common English language words. These are terms that are used by geologists to describe igneous rocks based upon their silica content. Most of the igneous rocks can be classified as Mafic or Felsic. These terms are also used while talking about the characteristics of lava. Many students confuse between the two adjectives Mafic and Felsic. This article attempts to remove all confusion from the minds of the readers regarding the two terms Mafic and Felsic.

Mafic

Mafic is an acronym made up of Ma that stands for Magnesium and Fic that stand for iron or ferric, the Latin name of iron. Thus, it is clear that these igneous rocks are rich in magnesium and iron. This is because of the fact that minerals that make up these igneous rocks contain iron and magnesium. Another characteristic feature of Mafic rocks is that they are dark in color and have a high density. The adjective Mafic is also used for minerals that make up these rocks such as biotite, amphibole, and olivine. The most common examples of rocks classified as Mafic are gabbro, dolerite, and basalt. Silica content in Mafic rocks is around 50% by weight. Most of these rocks are gray though Mafic rocks are also found in brown, green, and even black colors.

Felsic

Felsic is a term that is used to refer to igneous rocks rich in mineral feldspar. Felsic is a term that is made up of the names of Feldspar and silica. Feldspar is a mineral that contains a high percentage of silica and aluminum. These are igneous rocks that have a lower density than mafic rocks and are also lighter in color. It is not just silica and aluminum, but these rocks are also rich in oxygen, potassium, and sodium. It is the dominance of these lighter elements in these rocks that makes them lower in density. Granite is a great example of Felsic rocks and muscovite, quartz, and some feldspar are the best examples of Felsic minerals. All Felsic rocks contain a high percentage of silica. For example, granite contains around 70% of silica.

Mafic vs Felsic

• Mafic and Felsic are categories into which igneous rocks are classified.

• Silica is the most abundant material found in igneous rocks. This is why silica content has been chosen to classify igneous rocks with higher silica content making a rock Felsic while lower silica content making them Mafic. Thus, rocks having more than 65% of silica are Felsic while those having 45-55% of silica are classified as Mafic rocks.

• Mafic rocks are rich in iron and magnesium, whereas Felsic rocks are rich in silica and aluminum.

• Mafic rocks are denser and heavier than Felsic rocks.

• Mafic rocks are darker in color than Felsic rocks.

• Lava made up of Felsic rocks is slow moving and has a higher viscosity than Mafic lava.