Stalactites & Stalagmites
activity exercisesuggested grade levels: 4-8

view Idaho achievement standards for this lesson

Stalactites and stalagmites are cone-shaped formations which look a little like huge icicles of rock. They are found in caves. They are calcium deposits made by calcium-laden water dripping through the ceiling and onto the floor of the cave. The water evaporates, leaving the calcium behind. These calcium deposits are formed in two ways: a stalactite forms like an icicle hanging from the cave roof. When the calcium water drips to the floor and the deposit builds upward, a stalagmite is formed.

cardboard box 2 tall jars
heavy cotton string Epsom salts
2 nails  

Use the Caves section of the Digital Atlas of Idaho to learn about the natural formation of stalactites and stalagmites. To get there: Click on Idaho Overview, then on Caves. Scroll down and read through the material on caves as a review. Discuss as a class:

1. The different types of caves.
2. How these different types of caves form.
3. Formation of stalactites and stalagmites.

Activity: (Students should work in groups of 3-4)
Place a tall jar on either side of an open-topped box. Tie four pieces of heavy string to two nails. The strings must be long enough so that they reach from one jar, over the box, to the bottom of the jar on the other side. The strings should also be loose enough so they hang down slightly into the box.Make a solution of Epsom salts and water. You may add food coloring if you wish. Fill the jars with the salt solution. Place a nail in each jar with the strings leading over the cavern. Water and salt will move up the cord. As the water evaporates, it will leave the salt to accumulate in the same way calcium does in real stalactites and stalagmites. Leave it alone for a week. Soon, "icicles" will form stalactites hanging from the string. Stalagmites will form on the cave floor as the dripping water evaporates to leave behind a cone of salt.

Handouts/Activity links:
These are links to access the handouts and printable materials.

Related Lesson Topics:
Geology: Geology Topics

Lesson plan by Dr. Helen Challand and Elizabeth Brandt with permission from Science Activities from A to Z, illustrations by Herb Rudd, 2001
Idaho Achievement Standards (as of 7/2001) met by completing this activity: