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Entry Category: Geology - Starting with R

Rocks and Minerals

There are three basic classes of rocks: igneous, metamorphic, and sedimentary. Igneous rocks are those that solidified from magma (molten rock). Metamorphic rocks are formed from pre-existing rocks in a solid state by heat, pressure, and/or chemical activity. Sedimentary rocks are made up of particles of sediment cemented together. In Arkansas, the overwhelming majority of surface and near-surface rocks are sedimentary rocks. There are a few igneous rocks and some very low-grade metamorphic rocks, but these occupy little area. Out of Arkansas’s total area of 53,179 square miles, only about fifteen square miles are composed of igneous rocks. In the Ozark Plateau and Ouachita Mountains, there are indications of some very low-grade metamorphic effects on the rocks in restricted areas, …