Sci 245 Week 4 Checkpoint

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Igneous Rocks |

Sci. 245 Week 4 Checkpoint |

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Bree Odion |

7/15/2011 |

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Igneous rocks originate within volcanoes from the earth’s crust magma. These are formed when a volcano has erupted, where the magma will rise to the above the earth’s surface. When this happens it is call lava, which is how Igneous rocks form after the lava cools down. There are two different types of igneous rocks that are Extrusive (volcanic) and Intrusive (plutonic). Igneous rocks form by crystallizing magma. They can either form on the outside or the inside of the volcano. The ones that form on the inside of the volcano are called intrusive and the ones that form on the outside are considered extrusive. Volcanic rocks (extrusive) crystallize from lava on the outside of the volcano whereas Plutonic (intrusive) form on the inside of the volcano from magma.

There are a few factors that determine the differences between the two categories of igneous rocks. The main factor though is the rate of cooling. Volcanic rocks are on the outside therefore they cool faster due to the elements of air and water. When the rock cools faster it does have the time to produce larger size grain within the rock. Plutonic rocks have time on the inside without the outside elements to cool slowly and produce larger size grain. This really determines the difference in the texture between the two rocks. The other difference between the two would be the level of silica within the rock. This determines the color of the rock as well. Those with large amounts of silica are usually light in color and those rocks that have lower amounts of silica are darker in color and mineral.

References

Axia College. (2011). Visualizing Geology. Retrieved July 15th, 2011, from Axia College, Week Four, SCI 245.

http://www.wiley.com/college/strahler/0471480533/animations/ch12_animations/animation1.html