Is Diorite Felsic or Mafic? (Answered)

Diorite is classified as an intermediate rock between felsic and mafic rocks.

Diorite has a granular texture and visible crystalline structure, distinguishing it from felsic and mafic rocks.

The following article discusses the physical and chemical characteristics of diorite rocks and the properties of mafic and felsic rocks.

Is Diorite Felsic or Mafic? (Explained)

Diorite Facts

Diorite is a coarse-grained intrusive igneous rock composed of crystals that are randomly aligned with large interlocks.

The rock is formed from cooling magma deep below the earth’s crust.

Due to the slow cooling rate of diorite, which is comparable to that of most intrusive igneous rocks, diorite often features large crystals.

Diorite is composed of silica-rich magma, but not as much as felsic.

Additionally, it contains less than 35% mafic material, disqualifying it from being classified as a mafic rock.

Further, diorites do not contain predominantly dark or light-colored minerals.

As a result, the physical appearance of the rock is often characterized by contrasting white and black mineral grains, which are referred to as a mesocratic color index.

The structural properties of diorites resemble those of granite with its dark-gray color.

The rock’s chemical makeup positions it between acidic and alkaline.

Its alkaline character is due to the presence of feldspar, whereas its acidic character is due to the presence of silica and calcic pyroxene.

Plagioclase, which has a lower calcium level than sodium, accounts for 90% of the feldspar in the rock.

Plagioclase is the most abundant mafic component in diorites, with less abundant hornblende.

Additionally, zircon, ilmenite, titanite, apatite, magnetite, olivine, biotite, and orthopyroxene are present.

Other rocks comparable to diorite include gabbro, which contains plagioclase and pyroxene, and granitoid such as tonalite and granodiorite.

Felsic vs Mafic

Depending on its silica content, a rock is classified as felsic or mafic.

A rock with a silica content of 0% to 45% is classified as mafic, whereas a silica content of more than 65% is classified as felsic.

Intermediate rocks have a silica concentration of between 45% to 65%.

For example, with a silica concentration of 59%, diorite is classified as an intermediate rock.

By contrast, felsic is composed of feldspar and silica.

The term “Mafic” is derived from ‘MA’ for magnesium and ‘FIC’ for the Latin name of iron.

The term “Felsic,” on the other hand, is derived from a combination of ‘FEL’ for the potassium-rich feldspar and ‘SIC’ for silica.

An excellent example of a felsic rock is granite, while mafic rock may include gabbro and basalt rocks.

The importance of ascertaining whether a rock is felsic or mafic is to establish the likelihood of specific minerals being present in the rock.

Felsic rocks, for example, are considered rich in potassium, aluminum, oxygen, and silicon minerals, while mafic rocks are rich in magnesium and iron minerals.

These minerals are essential for industrial purposes, as is determining the locations of rocks rich in certain minerals.

Diorite rocks are half-dark and half-light due to biotite, hornblende, quartz, calcium plagioclase, and sodium.

Since diorite has 59% silica, it is classified as an intermediate rock, as opposed to mafic rocks, which contain less than 45% silica, and felsic rocks, which contain more than 65% silica.

In that case, diorite contains less mafic mineral content and less felsic mineral content.

What Is Diorite Used For?

Since diorite is durable compared to trap rock and granite, it is crushed and used as base material in construction projects where it is readily available.

It is used in buildings, roads, erosion control, parking areas, and drainage construction projects.

It is also cut into curbing, pavers, blocking, ashlars, tiles, and facing stones in the stone industry.

Some industries polish the diorites and use them for architectural purposes.

The diorite construction and architectural technology can be traced back to the ancient Middle Eastern civilization and the South Americans during the Mayan and Incan civilizations.

Additionally, since diorite can be polished and used in art, where it is cut and used as gemstones.

Australia’s ‘pink marshmallow stone’ is an excellent example of cut pink feldspar phenocryst-rich diorite.

However, due to its coarse-grained size and hardness, diorite is considered unfavorable to sculptors’ work, although it was popular among ancient Middle Eastern sculptors.

A good example is the Code of Hammurabi sculpture erected in 1750 BC, inscribed with the Babylonian laws.

Diorite was chosen for that very purpose because of its durability.

Conclusion

Diorite, a rock with a monocratic color index, is classified as an intermediate rock that falls between felsic and mafic rocks.

The hue of felsic rocks is lighter, whereas mafic rocks are darker.

The term “Mafic” refers to a mixture of magnesium and iron constituents.

By contrast, felsic is composed of feldspar and silica.

On the other hand, diorite rocks are half-dark and half-light due to biotite, hornblende, quartz, calcium plagioclase, and sodium.

Since diorite has 59% silica, it is classified as an intermediate rock, as opposed to mafic rocks, which contain less than 45% silica, and felsic rocks, which contain more than 65% silica.