Chemical composition. Especially when Basic\Mafic.
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Igneous rocks get darker as a result of higher concentrations of dark minerals like mafic minerals (e.g., biotite, amphibole, pyroxene) and higher levels of iron and magnesium. These minerals are more abundant in mafic igneous rocks, leading to their darker coloration compared to felsic igneous rocks, which have lower levels of these dark minerals. Heat also plays a role in darkening certain minerals through processes like metamorphism.
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.
Dense. Light colored igneous rocks have lower density compared to dark colored igneous rocks due to their higher silica content, which results in slower cooling and the formation of larger crystals.
Rhyolititcen rocks.
Igneous rocks are formed by the solidification of molten materials.
No, igneous rocks are formed from the cooling and solidification of magma or lava. They are not made up of pre-existing igneous rocks.