The Influence of Mafic and Metal on Volcanic Activity

Mafic vs. Felsic Mafic and felsic are terms used to describe types of rocks based on their mineral composition and chemical properties. These terms are commonly used in the field of geology to categorize and classify different rock types. Mafic rocks are characterized by a high content of magnesium and iron, as well as relatively low levels of silica. They are typically dark in color and have a dense, heavy appearance. Basalt and gabbro are two common examples of mafic rocks.

Basalt and gabbro are two common examples of mafic rocks. Felsic rocks, on the other hand, have a low content of magnesium and iron, and a high level of silica. They are typically light in color and have a less dense, lighter appearance.

felsic and mafic rocks

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felsic and mafic rocks, division of igneous rocks on the basis of their silica content. Chemical analyses of the most abundant components in rocks usually are presented as oxides of the elements; igneous rocks typically consist of approximately 12 major oxides totaling over 99 percent of the rock. Of the oxides, silica (SiO₂) is usually the most abundant. Because of this abundance and because most igneous minerals are silicates, silica content was used as a basis of early classifications; it remains widely accepted today. Within this scheme, rocks are described as felsic, intermediate, mafic, and ultramafic (in order of decreasing silica content).

In a widely accepted silica-content classification scheme, rocks with more than 65 percent silica are called felsic; those with between 55 and 65 percent silica are intermediate; those with between 45 and 55 percent silica are mafic; and those with less than 45 percent are ultramafic. Compilations of many rock analyses show that rhyolite and granite are felsic, with an average silica content of about 72 percent; syenite, diorite, and monzonite are intermediate, with an average silica content of 59 percent; gabbro and basalt are mafic, with an average silica content of 48 percent; and peridotite is an ultramafic rock, with an average of 41 percent silica. Although there are complete gradations between the averages, rocks tend to cluster about the averages. In general, the gradation from felsic to mafic corresponds to an increase in colour index (dark-mineral percentage).

The fine-grained or glassy nature of many volcanic rocks makes a chemical classification such as the felsic-mafic taxonomy very useful in distinguishing the different types. Silica content is especially useful because the density and refractive index of natural glasses have been correlated with silica percentage; this makes identification possible in the absence of chemical data. For similar determinations, glasses can also be prepared in the laboratory from crystalline rocks.

The influence of silica content on the particular minerals that crystallize from a rock magma is a complex interaction of several parameters, and it cannot be assumed that rocks with the same silica content will have the same mineralogy. Silica saturation is a classification of minerals and rocks as oversaturated, saturated, or undersaturated with respect to silica. Felsic rocks are commonly oversaturated and contain free quartz (SiO₂), intermediate rocks contain little or no quartz or feldspathoids (undersaturated minerals), and mafic rocks may contain abundant feldspathoids. This broad grouping on the basis of mineralogy related to silica content is used in many modern classification schemes.

This article was most recently revised and updated by John P. Rafferty.

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Granite and rhyolite are two well-known examples of felsic rocks. One of the main differences between mafic and felsic rocks is their mineral composition. Mafic rocks typically contain minerals such as pyroxene, olivine, and amphibole, whereas felsic rocks often contain minerals such as quartz, feldspar, and muscovite. Mafic rocks also tend to have a higher density and a higher melting point compared to felsic rocks. This is due to their higher content of heavy elements like magnesium and iron, which contribute to their dense nature. In terms of volcanic activity, mafic lavas have a more fluid and runny consistency, whereas felsic lavas are more viscous and sticky. This is because mafic lavas have a lower silica content, which allows them to flow more easily, while felsic lavas have a higher silica content, which makes them thicker and harder to flow. Mafic and felsic rocks are also associated with different tectonic settings. Mafic rocks are commonly found in areas of volcanic activity, such as mid-oceanic ridges and hotspots. Felsic rocks, on the other hand, are often associated with continental areas and are more commonly found in regions with past or present tectonic activity. In conclusion, mafic and felsic rocks are two distinct types of rocks with different mineral compositions, densities, melting points, and volcanic behaviors. Understanding these differences is crucial in the field of geology, as it helps geologists identify and classify various rock types and interpret their geological significance..

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The Implications of Mafic and Metal for Ore Deposits