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Igneous Rocks

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Moon Rock Counter
Teacher Contributed

Moon Rock Countertops

Topic

Optical Mineralogy and Petrography

Student Exploration

Have you ever seen anything like this? What do you think this is?

Would you believe that this could be a slice of your kitchen countertop? This image of the igneous rock, benzatite, is a very thin slice that was put under a cross-polarized light microscope. Petrologists use rock thin sections like this one to learn more about the composition of the rock and the temperature and pressure conditions that were present during the rock’s formation.

Could petrologists use this same technique to better understand rock samples that have been collected over the years from the surface of the moon?

Extension Investigation

  1. Practice being a petrologist yourself! Here is a sample of gabbro: Use http://www.open.ac.uk/earth-research/tindle/AGT/AGT_Home_2010/Object-S276-gabbro.html Use the following link to manipulate a virtual microscope that is focused on a thin section of that same piece of gabbro:http://www.virtualmicroscope.co.uk/sites/www.virtualmicroscope.co.uk/files/imagecache/400px/gabbro%20xpl.JPG
    1. In the virtual microscope, the first view is of plane polarized light. If you click on the xpl option on the bottom left, the image will be reloaded in cross-polarized light. What happens when you do this? Write down your observations.
    2. On the bottom of the image, there is also a zoom option. Click on the plus sign to increase the magnification on the thin section. What do you notice? Write down your observations.
    3. At the top right of the image, there are four options (r1, r2, r3, and r4) that zoom in to four particular places on the thin section. Click on one of them. It will show the plane polarized view and the cross-polarized view side by side. Make a sketch of the view.
    4. After using all of these tools on the virtual microscope, how do you think that petrologists determine the rock’s composition? How do you think that they determine the pressure and temperature of the rock’s formation?
  2. Compare the three types of rocks under the virtual microscope! Use the links above for the igneous rock type. For sedimentary rocks, use this sample of limestone: For http://www.virtualmicroscope.co.uk/projects/sediment/crinoidal-limestone-slide For metamorphic rocks, use this sample of schist: What http://www.virtualmicroscope.co.uk/projects/metamorphic/garnet-mica-schist-slide What is similar? What is different? What data from these three thin sections help to identify them as sedimentary, igneous, or metamorphic?
  3. Do you think that rocks from the moon look similarly in thin section? Let’s take a look! The following two samples are actual samples from the surface of the moon that were collected during the Apollo 17 mission in December of 1972. Sample A: Sample http://www.virtualmicroscope.co.uk/projects/moonrocks/78235-norite-melt-vein-slide Sample B: For http://www.virtualmicroscope.co.uk/projects/moonrocks/70017-high-titanium-basalt-slide For each sample, draw a sketch. Under each sketch predict the rock type (sedimentary, igneous, metamorphic) and provide an explanation for your prediction.

Resources Cited

Tilman.Wikimedia Commons.http://upload.wikimedia.org/wikipedia/commons/e/e6/Bronzitite.jpg

The Virtual Microscope for Earth Sciences.The Open University.http://www.virtualmicroscope.co.uk/

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