An igneous rock that contains many non-ferromagnesian silicate minerals has which composition?
The Correct Answer and Explanation is:
An igneous rock that contains many non-ferromagnesian silicate minerals is described as having a felsic composition. Felsic rocks are rich in lighter-colored minerals, primarily quartz and feldspar, and have a higher concentration of silicon and oxygen compared to magnesium and iron. These rocks typically form from the cooling and solidification of magma that is low in iron and magnesium but high in silicon dioxide (SiO₂).
Felsic igneous rocks are usually lighter in color, with shades ranging from white to light gray, pink, or red, depending on the mineral content. The term “non-ferromagnesian” refers to minerals that lack significant amounts of iron (Fe) and magnesium (Mg). Common minerals found in felsic rocks include quartz, orthoclase feldspar, plagioclase feldspar, and mica. These minerals are generally lighter in color and have lower densities compared to ferromagnesian minerals, which are richer in iron and magnesium.
Felsic rocks have relatively low melting points, and they crystallize from magma that has undergone extensive differentiation, making them more evolved in composition. As a result, felsic rocks tend to be associated with continental crust, as opposed to the darker, more mafic rocks typically found in oceanic crust. Examples of felsic igneous rocks include granite, rhyolite, and obsidian.
In terms of mineral composition, the higher proportion of silica in felsic rocks influences their properties. For example, felsic rocks tend to be less dense and more viscous compared to mafic rocks, which means that the magma from which they form tends to be more resistant to flow. This can lead to explosive volcanic eruptions, which are characteristic of felsic volcanic activity.
Thus, igneous rocks with a high proportion of non-ferromagnesian silicate minerals are classified as felsic, reflecting their lighter color, higher silicon content, and mineral composition.
