New Ask-a-Geologist Question: Rock Types

Question: What are the three big groups of rocks?

Answer: The three basic rock types are Igneous, Metamorphic and Sedimentary.  Igneous rock form from hot liquid magma. The magma either erupts from a volcano, cools and hardens into extrusive igneous rocks, or forms intrusive igneous rock when the hot magma is trapped beneath the earth’s surface, cools and hardens.

Sedimentary rocks are formed when sand, small pieces or rock, or mud are pressed together to form layers of sediment. These layers of sediment are pressed together over a long period of time and form a sedimentary rock.  A metamorphic rock is formed when a sedimentary or igneous rock changes form because the temperature or pressure changes. This change typically occurs over time when the sedimentary or igneous rocks are buried beneath the earth’s surface.

Read the article titled Geology is All Around You in the “Dig Into Geology” section of our website for more information on these rock types, minerals and the geologic time scale.

One Response to “New Ask-a-Geologist Question: Rock Types”

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