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sci 245 ig. rock - surface The pockets of trapped magma...

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Understanding igneous rocks requires knowing where and how these specific rocks form. The word igneous means fire in Latin. According to the National Park Service, igneous rocks are “formed by the cooling and hardening of melted rock material” (Summary, para. 1). The melted rock material is better known as magma and lava. Magma is the hot molten rock that exists beneath the earth’s surface. When this hot molten material erupts through volcanoes to the earth’s surface it becomes lava. Igneous rocks form when lava and magma cools and hardens. Two main categories of igneous rocks exist depending upon how and where the rocks develop. Volcanic rocks form when lava cools and crystallizes above the earth’s surface, and plutonic rocks from underground when magma cools and crystallizes. Intrusive rocks sometimes called plutonic rocks, form when melted magma flows into small crevices and pockets underneath the earth’s
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Unformatted text preview: surface. The pockets of trapped magma cool very slowly. Slowly cooling magma results in large mineral crystals rocks known as phaneritic. Plutonic rocks are usually light in color because of the high silica content; these rocks are also known as felsic rocks. Intrusive rocks can occur in different shapes in sizes. Volcanic rocks, sometimes called extrusive rocks, cool rather quickly. Extrusive rocks are usually dark in color because of the low silica content. Sometimes these low silica high iron rocks are known as mafic rocks. When mineral crystals are present in volcanic rocks, they are usually microscopic and known as aphanitic. Sometimes crystals are absent from volcanic rock because of how rapidly these rocks cool. References National Park Service U.S.Department of the Interior. (2007). Igneous rocks. Retrieved May 27, 2011 from: http://www.nps.gov/brca/forteachers/randmact3.htm...
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