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Igneous Rock Classification

Igneous rocks are grouped based on silica content and whether the rock is extrusive or intrusive.

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Yosemite Rocks!

Yosemite Rocks!

License: CC BY-NC 3.0

The world over, Half Dome means Yosemite. And Yosemite is what it is because of its hard granite rock.

Amazing But True!

  • The Farallon Plate subducted beneath the North American Plate.
  • Subduction created a giant magma plume 100 miles long. 
  • The magma cooled slowly deep in the crust and became the Sierra Nevada granite batholith.
  • Hard minerals from the cooled magma are resistant to erosion.
  • It is possible to see some of the history of the magma and magma chambers in the polished rock of Yosemite.

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

  1. Why does the rock of Yosemite have so many large, hard crystals that stick out of it? (Hint: this is a two part question.)
  2. Why is the granite so solid, displaying so few cracks?
  3. In the video, there are two different rocks in contact with each other: one is a light colored granitic rock with large crystals, the other is darker with smaller crystals. Think of some possibilities for the history of this exposed rock face.
  4. How could glaciers carve the Sierra Nevada so spectacularly but not other places that they flowed over?
  5. Much of the rock of Yosemite is granite, but some is more intermediate. What minerals do you expect to see in granite and in more intermediate rock?

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  1. [1]^ License: CC BY-NC 3.0

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