Growing Salt Crystals is a Fun Geology Experiment for Kids (and adults, too)!

Hey Mini Me Geologists! Try this fun experiment to learn more about growing salt crystals. Did you know that the salt you put on your food is actually a mineral? Salt forms naturally by precipitation or evaporation. In this experiment, you will watch salt crystals form by precipitation because it is just more fun than watching water dry and leave salt behind, although you can try that method, too. Grab an adult to help you with the stove and boiling water but the rest you can do on your own. In nature, salt will precipitate from mineral-rich water in oceans or lakes so you will simulate ocean water to grow your crystals.

You will need:

  • Clean Jar
  • String (cotton works best)
  • Scissors
  • Tape (optional)
  • Pencil
  • 1-2 Cups boiling water (parents and teachers, this is your job)
  • 1-2 Cups table salt
  • Spoon
  • Notebook
  • Camera (optional)
  • Oven mitts (optional, but handy)

Step 1: Boil the water and then transfer it to your clean jar. You can boil the water on the stove or use a microwave. The important part is to make sure that the water is rapidly boiling before you begin Step 2. As you handle the jar, wear oven mitts or only touch the areas, like the rim, that are not overheated by the boiling water. We don’t want any burned fingers!

Step 2: Pour enough salt into the jar to saturate the water. Stir until all of the salt that can dissolve is dissolved. If you see salt crystals in the bottom of your jar that will not dissolve then you have probably saturated your water and are ready for Step 3.

Step 3: Tie a piece of string to a pencil and hang the string in the water. Rest the pencil across the top of your jar and tape it in place if necessary. Make sure that the string does not touch any of the salt at the bottom of the jar.

Step 4: Observe the jar over the next few hours. You should begin to see small crystals form on the string. Leave the string in the jar overnight.

Step 5: The next day, take the string out of the jar and observe if salt crystals have formed on the string. Salt crystals may take some time to get large so if you want to grow large crystals, replace the salt water solution daily. Don’t forget to document your experiment. We would love to see photos of your crystals and let us know how you do in the comments below.

Tip for Teachers: You can do this salt experiment in a classroom setting or a camp with great success. The salt crystals should form rapidly and if you use mason jars with lids the kids can take their solution home and observe for several days. Do not attempt sugar crystals in a classroom because you really need to dissolve the sugar on the stove top in order for the experiment to work.

You can find more great activities like these in our Rock Cycle Kit and Rock Detectives Kits!

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