Igneous rocks (from the Greek word for "fire") form when hot, molten rock (magma) crystallizes and solidifies. Magma originates deep within the Earth, near active plate boundaries or hot spots. Magma that rises to the surface is called lava. Igneous rocks are classified into two groups depending upon where the molten rock solidifies: extrusive or intrusive.
Felsic: Derived from the words feldspar and silica to describe an igneous rock having abundant light-colored minerals such as quartz, feldspars, or muscovite.
Mafic: Derived from the words magnesium and ferric (Fe is the chemical symbol for iron) to describe an igneous rock having abundant dark-colored, magnesium- or iron-rich minerals such as biotite, pyroxene, or olivine.