Source: Mineralogical Society of America.
Adapted with permission.
Most minerals happen naturally as crystals. Crystals are made of specific atoms or molecules joined to make distinctive repeating patterns. The crystals that make up many kinds
of minerals are formed deep underground through the interaction of fluid, pressure, and temperature. Some minerals form at or near the surface. You may have seen spectacular mineral samples in museums, but you might not be aware that minerals are everywhere, including in your body.
In this activity, you will explore the interaction of water (fluid), heat, and the mineral halite or the salt sodium chloride. You will observe what happens when salt crystals form at both room temperature and at a refrigerated temperature.
Practice safety: You will be dissolving table salt into hot water in two separate containers. Working with hot water is always hazardous, so work with an adult and be careful when stirring the solutions in the containers.
• Hot water
• Stirring spoon
• Measuring teaspoon
• Paper for recording observations
• 2 white 3”x5” cards
• Pencil for labeling
• Granular table salt
• Two clear 8 oz heatproof containers
• Metric ruler
• Coarse string
• Safety scissors
• 2 flat table knives
• 2 medium paperclips
• Piece of black paper
• A safe place where the containers will be undisturbed for several days (one container at room temperature, the other in a refrigerator)
- Put some salt onto the black paper and view it through the magnifier. What do you see? Draw the shapes of the salt crystals.
- Make two labels on the 3”x5” cards. One should say “Room Temperature Salt” and the other “Refrigerator Salt.” Date each card.
- Ask an adult to pour 6 fluid ounces of hot water into one container. Add salt to the container, teaspoon by teaspoon, stirring each time until the salt is dissolved. Keep adding salt until it no longer dissolves.
- Repeat step 3 with the second container.
- Cut two pieces of string long enough to hang about 2 cm from the bottom of each container. Leave enough string to tie around the handle of the table knife. Tie the string to the two knives and hang a paperclip on the middle of the string. Rest the knives on top of the containers and put one container carefully into a safe place at room temperature. Put the second container in the refrigerator. Put the labels by the containers, so that you can identify them.
- Observe the containers each day for several days and see what happens around the containers’ sides and on the strings. When you several crystals have grown, take the strings out of the container and once again look at them through the magnifier. How are they the same and/or different from the original salt crystals and from each other? Why do you think that is so?
• Do some research to find out what happens to water when salt crystals form.
• Find more information about minerals and crystals at MSA’s Mineralogy4Kids: www.mineralogy4kids.org