From San Diego Natural History Museum Website


A mineral is an inorganic, naturally-occuring crystalline solid. This means that minerals form as crystals. Some mineral crystals, like halite (table salt when it's in your kitchen cupboard) are created by precipitation. The minerals precipitate out of a solution and collect into their crystal forms. With a few household items, you can use this process to grow your own crystals.

CAUTION! Performing this experiment requires boiling water. Be careful to avoid injury or ask an adult to help you.

Gather Your Equipment

To make your own salt crystals, you'll need a few items from around the house.

A heat-proof, glass jar (a mason jar is excellent.)
A measuring cup
About 1 cup of boiling water
About 1/2 cup of salt
A pencil
Cotton string
A spoon
A paperclip
A paper towel

Now it's time to prepare a supersaturated solution.

Prepare a Supersaturated Solution

Tie the paper clip to one end of the string, and the pencil to the other end. When you place the pencil across the top of the jar, the string should be just long enough to let the paper clip touch the bottom. Set the string, pencil, and paper clip aside.

Boil about 1 cup of water, either in the microwave or on the stove. Pour the boiling water into the jar. Add the salt one teaspoonful at a time. Stir until each teaspoon is completely dissolved. You may be tempted to add all the salt at once, but the experiment won't work as well if you do. Be patient. Eventually, you'll find a small amount of salt will not dissolve and collects at the bottom of the jar. You have reached supersaturation. Once the solution is supersaturated, stop adding salt.

Next, you'll put it all together -- and find out what to do with that string and the paper towel.

Put It All Together

Lower the paper clip and string into the water and rest the pencil across the top of the jar. Cover the jar lightly with a paper towel. This will keep dust out of the jar. Place the jar where it won't be disturbed for a couple of days.

Table salt (halite) crystals form as cubes. After about 12 hours, you should be able to see small crystals forming at the bottom of the jar, on the paper clip, and along the string. Some may even form on the surface of the water, like a wreath around the string. After 24 hours, you should see definite crystal forms.

After all this work, let's see the results and how to find out more about minerals.


Results and Resources

After one or two days, you'll be able to see cubes of salt crystals. Some may form alone and grow larger, while others may form clusters.

If you'd like to experiment with another mineral that has a completely different shape, try using 1 and 1/2 cups of Epsom salts (magnesium sulfate) instead of 1/2 cup of salt. The Epsom salt crystals will tend to form on the bottom of the jar and are generally shaped like stubby prisms.