why are dark igneous rocks heavier
Dark colored igneous rocks are high in iron and other heavier elements: ma-fic, magnesium-iron. Light color igneous rocks are high in aluminum and potassium. .ou need to understand one of the fundamental differences between mafic and felsic rocks. Mafic rocks contain larger amounts of Mg and Fe than felsic rocks. The atomic weights of Mg and Fe are higher than Al, Si, and O, therefore they tend to be heavier. Very simple concept.