Kids, how would you like to make your own rock? There are three major types of rock: sedimentary, metamorphic and igneous. This particular activity concerns sandstone, which is a type of sedimentary rock. You will need ½ cup (118 ml) of water, 2 paper cups, 2-1/2 tablespoons of Epsom salts (hydrated magnesium sulfate, MgSO4 which can be found at drugstores), and ½ cup (100 gm) of dry sand. Armed with these items you can perform your own geochemistry experiment!
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Put 1-1/2 inches (4 cm) of water in one of the paper cups. Dissolve the Epsom salts in this water. Stir with a spoon until almost all the salt has dissolved. These salts will act to cement the particles of sand together, just like certain minerals cement sand grains together in real sandstone. Now put 1-1/2 inches (4 cm) of sand in the bottom of the other paper cup. Pour the salt mixture into the sand and stir until the sand is completely wet. Let this slurry sit undisturbed for an hour. Then carefully pour off any clear water that has risen to the top. Repeat this several times throughout the day as needed until no clear water is left. Now set the cup aside, uncovered, and let it sit undisturbed for at least one week.
When your sandstone has dried completely, you will be able to tear the paper cup away from it. If anything is still damp when you try this, let the sandstone dry for a few more days and then try again. This might seem like a long time to wait, but it is eons shorter than the time it takes for real sandstone to form!
In nature, all kinds of sediment – pebbles, sand, clay, tiny dead animals, shells, plants – can be turned into rock. Most sedimentary rocks form under water. The process may take millions of years as sediment is slowly buried by more piling on top. As the pile gets heavier, particles on the bottom are squeezed and warmed by the heat of the earth. In addition to that, water that has minerals dissolved in it seeps in between the pieces and then evaporates. The minerals that are left behind cement the particles together into a larger rock.
A geochemist can see the results of these processes using a microscope. Sedimentary rock grains are smoothed by their journeys through water and are surrounded by the mineral cements. Using a magnifying glass, see if you can make out any of these features. Igneous rocks, on the other hand, are jagged and interlocked without any cement.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
June 2005
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References: “Geology Crafts for Kids: 50 Nifty Projects to Explore the Marvels of Planet Earth” by A. Anderson, G. Diehn, & T. Krautwurst. Sterling Publishing Co., NY, 1998, pg. 63. Also
http://www.coaleducation.org/lessons/sme/elem/17.htm.
