Question: what kind of rock can you grow? Answer: rock candy.
Rock candy is made of sugar crystals you can grow from a mixture of sugar and water. This can be done at home with simple materials. The process takes a few days.
CAUTION: This project involves the use of a stove to make a boiling sugar-water solution. Kids must do this with the help of an adult; sugar-water solution is extremely hot and can cause a bad burn if spilled.
Items you’ll need (prepare a few days ahead)
• cotton string
• a weight to hang on the string (such as a nail or paper clip)
• sugar for dusting the string
• small piece of waxed or parchment paper
• a pencil (to suspend the string in the jar)
To grow sugar crystals
• a measuring cup
• a small saucepan
• 2 cups water
• 4 cups sugar
• a wooden spoon
• a small, clean glass jar
1. Tie the nail to one end of the string. Tie the other end to the middle of the pencil. Moisten the string with water and dip into the dusting sugar. Remove it, straighten it out and lay it on a piece of waxed paper to dry for a few days.
2. Measure 2 cups of water and place in saucepan. Heat the water in the saucepan on the stove over medium-high heat until it comes to a boil.
3. Add the 4 cups of sugar a little at a time. It should completely dissolve in the boiling water. Stir continuously with the wooden spoon until the solution is clear and reaches a rolling boil. Remove the saucepan from the heat. Let the contents cool for 10 minutes, then carefully pour into the jar.
4. Suspend the prepared string in the jar, adjusting its length so that nothing touches the bottom or sides of the jar. Cover the jar with a small piece of waxed paper and let sit at room temperature, undisturbed, for several days. You can check each day to see how much your crystals have grown. Though you may be tempted, don’t touch the jar until the experiment is finished—it usually takes about seven days.
Growing crystals takes time because the crystals grow as the water evaporates. Cover the top of the jar with a paper towel or coffee filter to prevent dust from getting into the jar. Put the jar some place where it won’t be disturbed.
Check on your crystals every day. If a crust of crystals forms across the top of the jar, just remove it with a fork or spoon so water can continue to evaporate. If crystals form on the sides/bottom of the jar, pour the solution into a clean jar and place the string into the clean jar.
5) When your candy has grown big enough, you can take it out and eat it. To save it, just let it dry and then store it in a closed container. It won’t spoil, but if you leave it out, it may attract bugs.
To make the sample shown here, a few drops of red food coloring were added while the sugar-water solution was cooling. (Step 3)