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How to Make Rock Salt Crystals

Making crystals from rock salt, also called halite or table salt, is a simple and fun experiment that can be enjoyed by people of all ages. The process rests on the concepts of evaporation and crystallization. The liquid salt mixture that you will be preparing evaporates at a rate that exceeds the time it takes for the concurrent process of crystallization. The liquid evaporates and leaves the crystals, which appear as a dirty white color. The crystallization of rock salt is evident within six hours and peaks at three days.

Things You'll Need

Porous rock (pumice, clay or charcoal work best)
Shallow bowl or plate
Food coloring (optional)
Petroleum jelly (optional)
4 tbsp. salt
4 tbsp. liquid bluing
4 tbsp. room temperature water
4 tbsp. ammonia
Spoon
Mixing bowl

Instructions

- 1
  Place porous rock onto the center of the plate or shallow bowl where you will be growing your rock crystals.
- 2
  Add a few drops of your favorite color of food coloring, or a combination of colors, to the bottom of the bowl and onto the porous growing medium if you wish to enhance the aesthetic value of your salt crystals. The color will leach into the crystals.
- 3
  Coat the sides of the bowl or plate with petroleum jelly. This will cause the crystals to grow vertically instead of the natural pattern of horizontal spreading, keeping the crystals confined inside the bowl.
- 4
  Place salt, bluing, water and ammonia into the mixing bowl and mix well with the spoon.
- 5
  Pour the salt mixture over the porous growing medium.
- 6
  Repeat Steps 4 and 5 every three days until the crystals are the desired size.

Rocks & Minerals