How to Use Borax for Stalactites & Stalagmites

Stalactites and stalagmites in a limestone cave.

Stalactites and stalagmites are natural rock formations that occur in limestone caves. When acidic water drips from the ceiling of a cave it dissolves a portion of the limestone and carries down towards the ground. When the acidic water evaporates it leaves stalactites above hanging downwards and stalagmites below sticking upwards. A saturated solution of borax in water can be used to create crystalline stalactites and stalagmites by a similar process. The solution is first soaked up by cotton or some other fabric and as the solution drips and dries the borax crystallizes creating stalactites and stalagmites.

Things You'll Need

• Shoe box
• Pencil
• 30 inches of cotton string
• 2 pint jars
• 6 tablespoons of borax

Instructions

1. Punch a hole in one of long sides of a shoe box, 1/3 of the way down from the top of the box, using a sharpened pencil. The hole should be large enough for a piece of string to easily pass through.

2. Punch a second hole in the other side of the shoe box directly across from the first hole.

3. Place a string through the holes and tie knots near the side of the shoe box to stretch the string from one hole to the other. Leave 10 inches of string hanging from the outside of each side of the shoe box.

4. Bring a little more than 2 cups of water to a boil.

5. Pour 1 cup of boiling water into each of two pint jars.

6. Add 3 tablespoons of borax to each pint jar and stir the mixture until the borax dissolves.

7. Place the pint jars on either side of the box and put the hanging ends of string directly into the borax and water solution.

8. Wait for the string to soak up the mixture and begin to drip. The dripping will cause crystallized stalactites and stalagmites to form inside the shoe box.

References

• Jim Loy: Stalactites and Stalagmites
• Science Project Ideas: Growing Crystals
• The City of Ember Activities: Make Your Own Stalactites and Stalagmites