Remaining outcrops are (1) igneous rocks, mainly in the Wichita and Arbuckle Mountains, (2) metamorphic rocks in the eastern Arbuckles, and (3) mildly metamorphosed rocks in the core of the Ouachita Mountains. Rocks formed during every geologic period crop out in Oklahoma.
The most common rocks found in Oklahoma are sedimentary rocks, which are found on the surface, these rocks are composed of sediments which were lithified, in other words, they changed to stone. Other kinds of sediments include clay, sand and even sea shells. In other cases, sediment can be salt, as a result of when the sea dries up.
Another sedimentary rock is limestone. The limestone found in Oklahoma also contains marine fossils.
