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Intrusive and Extrusive Igneous Rocks

Intrusive rocks cool slowly and extrusive igneous rocks cool rapidly; this leads to different crystal sizes.

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Yosemite Granite

Yosemite Granite

Credit: Javier Velazquez-Muriel
Source: http://www.flickr.com/photos/javi_velazquez/6166613550/
License: CC BY-NC 3.0

From the front, Half Dome looks like a granite dome that lost half due to erosion. But from other angles, it is more like a thin ridge. Most of the dome is still there!

Amazing But True!

Credit: National Park Service
Source: http://www.nps.gov/yose/blogs/Mather-Musings-Whats-Under-Foot.htm
License: CC BY-NC 3.0

The Sierra Nevada mountains are composed mostly of granite [Figure2]

  • The Sierra Nevada Mountain Range is composed mostly of granite.
  • Sedimentary and volcanic rocks were metamorphosed as the granite plutons intruded.
  • Metamorphic rocks are found in the western portion of Yosemite National Park.
  • During the Pleistocene, the entire region was coated by glaciers.

Show What You Know

With the link below, learn more about Yosemite granite. Then answer the following questions.

  1. Why do the granites of Yosemite have such large crystals? What type of mineral forms the large knobs that climbers use for hand and foot holds?
  2. Why is granite such a strong rock?
  3. What happened when glaciers tried to erode the granite? What caused Yosemite Valley to form?
  4. When you see a dark colored granitic rock surrounded by a lighter colored granitic rock, how do you think it formed?
  5. What made some of the granite surfaces so smooth and shiny?

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Image Attributions

  1. [1]^ Credit: Javier Velazquez-Muriel; Source: http://www.flickr.com/photos/javi_velazquez/6166613550/; License: CC BY-NC 3.0
  2. [2]^ Credit: National Park Service; Source: http://www.nps.gov/yose/blogs/Mather-Musings-Whats-Under-Foot.htm; License: CC BY-NC 3.0

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