Generally, igneous rocks that are low in silica are dark relative to those that are high in silica. This tendency is largely the result of rocks low in silica having increased iron. Iron minerals tend to adsorb significant amounts of the visible spectrum and hence appear dark. I want to emphasize that this is a general tendency and there are exeptions -- obsidian which is very high in silica is typically a dark to black rock and a special igneous rock call carbonatite is very light in color but has little silica.
Light-coloured igneous rocks, such as granite, have a higher silica content and lower iron and magnesium than darker ones, such as basalt. Since iron and magnesium are very dense minerals, this makes darker igneous rocks more dense than lighter ones.
They are not low in silicate minerals. They are still primarily composed of them. However, the amount of silica in them is lower than in the lighter-colored rocks. The lightest igneous rocks (felsic) are at least 70% silica while the dark ones (mafic) are between 45% and 52% silica. Silica content below 45% is deemed ultramafic.
basaltic
Dark igneous rocks usually have higher amounts of heavier elements such as iron. Light-colored igneous rocks tend to be richer in lighter elements like sodium and aluminum.
Light colored igneous rock is called felsic, and is high in quartz, muscovite mica, and orthoclase feldsparcontent. Dark colored igneous rock is called mafic, and contains a lesser amount of silica along with olivine, pyroxene, amphibole, biotite mica, and plagioclase feldspar.
Mafic igneous rocks, like basalt, are dark colored and low in silica.
Mafic igneous rocks, like basalt, are dark colored and low in silica.
Mafic igneous rocks, like basalt, are dark colored and low in silica.
Light-coloured igneous rocks, such as granite, have a higher silica content and lower iron and magnesium than darker ones, such as basalt. Since iron and magnesium are very dense minerals, this makes darker igneous rocks more dense than lighter ones.
Normally, light colored igneous rocks are less dense compared to dark colored igneous rocks. This is because the light colored rocks have a less iron in them.
Igneous rocks that are dense and dark-colored are called basaltic rocks. They are formed from magma that is rich in iron and magnesium and poor in silica content.
Normally, light colored igneous rocks are less dense compared to dark colored igneous rocks. This is because the light colored rocks have a less iron in them.
less dense
They are not low in silicate minerals. They are still primarily composed of them. However, the amount of silica in them is lower than in the lighter-colored rocks. The lightest igneous rocks (felsic) are at least 70% silica while the dark ones (mafic) are between 45% and 52% silica. Silica content below 45% is deemed ultramafic.
Intermediate rocks contain roughly equal amounts of dark- and light-colored minerals. Igneous rock containing 56-65 percent silica.
basaltic
Dark igneous rocks usually have higher amounts of heavier elements such as iron. Light-colored igneous rocks tend to be richer in lighter elements like sodium and aluminum.