Basic rocks are composed of less than 52% silica and a large amount of plagioclase feldspar and very rarely quartz. The two most common types of basic rocks are basalts and gabbros. Ultrabasic rocks are composed of less than 45% silica and contain no quartz or feldspar. They are composed mainly of the minerals olivine and pyroxene. The most common ultrabasic rock is periodite. Periodite is a dark green, coarse-grained igneous rock that many scientists believe is the main rock of the mantle. Click on the "Next" button next to learn about the most widespread igneous rock.

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