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Home > For Teachers
> Crystallization Activity - Growing Rock Candy
As magma and lava cool to form igneous rocks, they form crystals. In this activity, you'll grow crystals too--sugar crystals to make rock candy!
Growing Rock Candy
What you will need: A clean one-quart large-mouth canning jar; a piece of clean white string; a metal weight, such as a paper clip or a metal washer; a pencil; a knife or fork; sugar; boiling water
The challenge: Discover how crystals grow and why some igneous rocks have larger crystals than others do.
Try it this way: Fill the jar with sugar. Slowly pour boiling water into the jar. Push a kitchen knife down into the water so that the sugar gets wet all the way down to the bottom of the jar. Add more water slowly and then stir to make sure that all of the sugar dissolves. Tie the paper clip weight to one end of the string. Tie the other end of the string to the pencil. Place the pencil across the mouth of the jar. Roll the string around the pencil until the weight is almost touching the bottom of the jar. Set the uncovered jar aside undisturbed in a warm place for several days. Crystals will grow on the string, on the jar, and on the surface of the sugar solution.
Break up the crust from time to time so that the water can evaporate. As the water evaporates, more crystals grow. Throughout this experiment, note the size of the crystals.
What happens and
why: As the sugar has more time to crystallize, the crystals
will grow larger. This is similar to the crystallization of igneous rocks.
When the rocks cool and crystallize above the surface of the Earth, they
don't have much time to form large crystals, so extrusive igneous rocks
have very small (or even nonexistent) crystal structures. When the rocks
cool and crystallize below the surface of the Earth where it's warmer,
they have a much longer time to form crystals. Thus, if you look at a
piece of granite, which is an intrusive igneous rock, you can see very
large crystals.
The Rock Cycle Web Site
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Webmasters: Chris
Lucas and Kate Seigfried
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This page was last updated on December 4, 2000
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