What are the four kinds of igneous rock?
Igneous rocks are usually classified first by their color index. The color index is separated into four categories. Felsic rocks are the lightest and are composed of mostly quartz and potassium feldspar. Intermediate rocks are the second lightest and are made up of mostly plagioclase feldspar, pyroxene, amphibole, and biotite. Mafic rocks are made up of plagioclase feldspar, pyroxene, and amphibole. Ultramafic is made up of mostly olivine, with pyroxene and amphibole.
