Geology And Geophysics

Understanding the three Basic Types of Rock



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All rocks can be classified into one of three categories: Igneous, sedimentary, or metamorphic.

Igneous Rocks form directly from cooled magma. The exothermic process of losing heat and cooling internally causes a phase change from magma's liquid state to its solid, crystalline state. As most people know, the Earth's core is made of molten magma; therefore, the hard exterior of the Earth's crust is formed from igneous rock which is the magma cooled by the lower temperatures of outer space. Igneous rocks are named based on their composition and texture, a feature described by the size of the crystals.

Loose sediment covers the layers of igneous rock that form the Earth's crust. These thin layers of debris are often compounded together through time, forming Sedimentary rocks. This second type of rock is made up of bits and pieces of existing rocks. There are three kinds of sedimentary rocks: clastic, chemical, and organic.

As time passes, changes occur on the Earth's surface, displacing rocks from their original locations to other locations. Essentially, any rock can become classified as a metamorphic rock if it is moved from the environment in which it was created into a new environment. One metamorphosis a rock can make is to be covered by dirt, buried, and compacted within the ground. Common variations of metamorphic rock include slate, gneiss, and marble.

All three types of rocks are entwined through the rock cycle, which maintains that igneous rocks create metamorphic rocks, which in turn create sedimentary rocks.

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