Friday, January 27, 2012

Crayon Rocks

We've had a very, very warm winter here in Michigan.  With such little snow, the ground has been exposed and my little rock hounds have been collecting rocks again.  I thought we'd revisit the types of rocks again (sedimentary, metamorphic and igneous) - but this time give them a more active and visual way to think about how each are formed.  There are many examples of creating rocks from crayons, but this pdf from the the Exploratorium is very helpful.

Materials Needed:
  • crayons, several of each in four different colors
  • crayon or pencil sharpener
  • 4 containers for holding the crayon shavings
  • 3-6"x6" pieces of aluminum foil
  • popsicle stick or other disposable stirrer
  • mug
  • boiling water

Unwrap the crayons and use the sharpener to create shavings.  You can also try to make the shavings use a penny or a plastic knife, although we found that the sharpener was easier and more productive than the penny or knife especially for the little ones.  Make sure to keep the shavings separate from each other at this point.

Sedimentary rocks
Sedimentary rocks are formed from sediments (tiny rock particles that were created by weathering or erosion) that were layered and then compressed.  To replicate this with the crayon shavings, take one of the aluminum foil squares and have your child sprinkle each of the colors of shavings into the middle of the square, one at a time so they will form the layers.

Fold the aluminum foil up tightly around the shavings and then compress it.  To do this, they can press on it with their hands, step on it, place it in a clamp or use your creativity to think of other ways.  .

This does take a while to get the crayon pieces to stick together and we found that a little body heat "helps" the process along.  Carefully unfold the foil and remove the sedimentary rock with care as this is the most brittle of the rocks that you are making.
A sedimentary crayon rock.

Metamorphic rocks
Metamorphic rocks are formed when existing rocks are exposed to heat and/or pressure.  To mimic this, take another square of aluminum foil and pile all four colors of shavings in the center.  Fold up the sides of the aluminum foil to make a boat.  Pour boiling water into a mug (adult job!) and float the boat in the hot water for 15 to 20 seconds, just until the shavings have started to melt.

Quickly remove the boat and fold the foil in half so that the shavings are compressed a bit. Let it cool and solidify and then open the foil and remove the metamorphic rock.
A metamorphic crayon rock.

Igneous rocks
Igneous rocks are formed when magma (molten rock) cools and solidifies.  To make an igneous crayon rock, repeat the steps for making the metamorphic rock, except leave the the aluminum foil boat floating on the hot water for a minute or more until all the crayon sediments have melted.  (This may take more or less time depending on the brand of crayons that you have used.)  Then take the popsicle stick and stir the shavings until they are all mixed together.  Remove the boat and let the crayon cool and solidify.
An igneous crayon rock.
If you are using a science journal to record your child's experiments, then you can have them record either the process of making each type of rock or draw a picture of what they looked like at the end (or both).

What's Happening?
There are three types of rocks (sedimentary, metamorphic, and igneous) which, given the right conditions, can be changed from one into another.  This is known as the rock cycle, pictured below.

Sedimentary rocks are formed from the compaction and cementation of rock sediments and often have distinguishable layers.  They also may have fossils of organisms or other visible rock particles in them.  Metamorphic rocks are formed when existing rocks are exposed to heat and/or pressure; they often have distinct bands or blocks of crystals in them.  Igneous rocks are formed when magma cools and their characteristics, including crystal size, depends on how fast the rock cools.  If it cools quickly on the surface of the earth (extrusive igneous rocks), the crystals are small and pores may be apparent.  If it cools slowly under the earth, the crystals have a chance to grow larger.  More information of rocks can be found in our Creating a Rock Collection activity.

One thing you could try is to create intrusive vs extrusive igneous crayon rocks.  Follow the directions to make two igneous rocks, but cool one in a glass of ice and the other at room temperature.  Examine the resulting "rocks" with magnifying glasses to see if there is any difference between them.  Please let me know if you try this - this is just a brainstorm idea and I really would like to know if there are any visible differences. 

If you are looking for a good children's book describing the rock cycle, we like the book "The Rock Factory: The Story about the Rock Cycle".  It probably is best for early elementary age kids.

Finally, you could try to make the different types of rocks with chocolate.  I'm thinking white, milk and dark chocolate.  Food + science - what a yummy combination!

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