Cave Formations: Stalactite and Stalagmite FormationFeatured science projectScience project video

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The dripping down (stalactite) and building up (stalagmite) will take about 3-5 days. If you want a column to form (the stalactite and stalagmite to touch), this will take over a week.
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Caves are amazing underground places. They are not just dark, damp places full of bats. Caves have features that are found nowhere else on Earth. Two such features are called stalactites and stalagmites. These are the icicle-like formations that hang from a cave ceiling and cone shaped formations that pile up on the cave floor. How did these fascinating cave features form? Just how does a stalactite and stalagmite form?


In this interesting earth science project, you will see first-hand how cave formations, called stalactites and stalagmites, form slowly over time through the dripping and hardening of minerals. You will get to speed up the natural process and create a model of a stalactite and stalagmite using Epsom salts, a common household mineral.


Caves are unique geological formations. Stalactites and stalagmites form very slowly over thousands of years through a rather simple process that all begins with dripping water. In fact, a stalactite or stalagmite grows only less than one inch each every 100 years.

Many caves are made of limestone, a rock that is easily dissolved. Since caves are usually found underground, rainwater constantly drips down through the roof of the cave. Minerals from the limestone are dissolved into the water. The mineral that is dissolved by the dripping water is called calcium carbonate, also known as calcite. As the water trickles down from the ceiling of a cave, it drips ever so slowly. Once the water hits the air inside the cave, the water evaporates and the calcite in the water hardens. This result is deposits of rock in the shape of a stalactite or stalagmite -stalactites, being the icicle-like formations that hang from a cave ceiling and stalagmites being the cone shapes that pile up on the cave floor. This process is called deposition, which comes from the word "deposit" meaning "to build up". If the deposition remains undamaged for long enough, the stalactite and stalagmite will touch and a column will form. The limestone rock of the cave, with the help of rainwater, has dissolved and hardened into a fascinating new shape!

stalactite and stalagmite scan

Scientific Terms

stalactites, stalagmites, dissolve, formation, hardening, deposition, minerals, calcium carbonate, limestone


  • two (2) small glass jars
  • one (1) small plate
  • wool or cotton yarn (thick is best)
  • baking soda or Epsom salt
  • 2 weights such as washers, heavy screws or fishing sinkers
  • water
  • spoon
  • paper and pencil
  • camera (optional)


1. Fill each jar about 2/3 full with hot tap water. Stir in as much Epson salt that will dissolve into each jar. Set aside for about 24 hours.

2. Take about 12-18 inches of yarn and tie one weight on each end.

3. Select a location that the stalactite and stalagmite model can be observed, but not bumped or moved. The formation created is very delicate!

4. Place the small plate between each jar. Place the ends of each string with the attached weight into jars. Place the jars far enough apart so that the middle of the string drapes in a "u" shape just above the plate.

5. After a few days check to see if any deposits are forming on the string or on the plate. Draw what you see every few days and label with the date, or take photos.

stalactite and stalagmite formation experiment


What is your stalactite and stalagmite made of? The stalactite and stalagmite in this model are made of Epsom salt.

2 .Where did the material on the string and the plate come from? The material on the string came from the dissolved Epsom salt, which dripped down through the string. The water then evaporated and the Epsom salt hardened once again, this time in the shape of a stalactite and stalagmite.

3. What does the string represent inside a cave? The string represents the cave ceiling.

4. Would this process take the same amount of time in a cave? The process takes much, much longer in nature. It takes hundreds of years.

Questions & Answers

What are the features in a cave called?

How are the features in a cave formed?

Make it Your Own

In this experiment you made a model of a stalactite and stalagmite from Epson salts, which is an easily dissolved, non-toxic mineral similar to the calcium carbonate that forms these structures in a cave. Research other common household materials that are also easily dissolvable, non-toxic minerals and try the experiment using these materials.


The Columbia Encyclopedia, Sixth edition. Columbia University Press (2007).

Stalactite and Stalagmite. Retrieved on November 15, 2013 from