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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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Rock Stars

Rock Stars


Credit: National Library of Ireland on The Commons
Source: http://en.wikipedia.org/wiki/File:Kissing_the_Blarney_Stone_1897.jpg
License: CC BY-NC 3.0

All rocks have an interesting geological history. Only a few rocks are important in human history. People have been kissing the Blarney Stone for centuries.

Famous Rocks

  • Plymouth Rock was a traveler, like the Pilgrims. It is a glacial erratic.
  • Some sources say that the Blarney Stone is a bluestone, but that’s not a rock type. The British call a rock of any origin that has been brought in from elsewhere a bluestone.
  • Credit: User:Huntster
    Source: http://en.wikipedia.org/wiki/File:Uluru_(Helicopter_view)-crop.jpg
    License: CC BY-NC 3.0

    Ayers Rock is sacred to the Anangu (Aboriginal people of the area) [Figure2]

  • Ayers Rock rises above the flat Australian Outback. The sandstone rock is a sacred site to the native people. Ayers Rock is a World Heritage Site.

Explore More/Show What You Know/Can You Apply It?

With the links below, learn more about a few famous rocks. Then answer the following questions.

  1. What type of rock is Plymouth Rock? How do rocks of that type form?
  2. What is the geologic history of Plymouth Rock? Why does the rock break fairly easily?
  3. What type of rock is the Blarney Stone? Which of the major rock types is that?
  4. What is the legend of the Blarney Stone?
  5. Why is Ayers Rock famous? What’s the geological history of the rock?

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Image Attributions

  1. [1]^ Credit: National Library of Ireland on The Commons; Source: http://en.wikipedia.org/wiki/File:Kissing_the_Blarney_Stone_1897.jpg; License: CC BY-NC 3.0
  2. [2]^ Credit: User:Huntster; Source: http://en.wikipedia.org/wiki/File:Uluru_(Helicopter_view)-crop.jpg; License: CC BY-NC 3.0

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