Igneous rocks that consist of dark-colored minerals have basaltic composition or are called basaltic rocks. Some geologists call basaltic rocks mafic rocks because basaltic rocks contain high percentages of dark silicate materials. Mafic is a term derived from the words magnesium and ferrum (which is iron in Latin). Since the iron content in basaltic rocks they are typically darker and denser then granitic rocks. One type of basaltic rock is basalt it is mainly composed of olivine, pyroxene and plagioclase feldspar. There are two types of basaltic rock one is intrusive which means it is course-grained. The other type is extrusive which means fine-grained. Basalt is the most common extrusive igneous rock. Many volcanic islands such as Hawaiian Islands are mainly made up of basalt. The intrusive equivalent of basalt is gabbro it is not commonly exposed on the surface but it makes up most of the ocean floor.