Olivine is the name of a group of rock-forming minerals that are typically found in mafic and ultramafic igneous rocks such as basalt, gabbro, dunite, diabase, and peridotite. They are usually green in color and have compositions that typically range between Mg₂SiO₄ and Fe₂SiO₄. Many people are familiar with olivine because it is the mineral of a very popular green gemstone known as peridot.