Grow Your Own Stalactite!

Experiment in progress
  • Subject: Science
  • Duration: 1/2 hour for preparing each demonstration, several days to see results
  • Age Level: Modify for all ages
  • Location: Indoors
  • Key Vocabulary: Speleothem, crystal

COMPETENCIES: The student will use the scientific method to investigate growing of stalactites and stalagmites. Students will be able to observe how representations of speleothems in a cave are formed.

OBJECTIVES: Students will be able to observe the process of speleothem formation.

BACKGROUND: Stalactites and stalagmites, collectively known as speleothems, form due to water seeping through rock. As the water moves through the rock, it dissolves small amounts of limestone or calcium carbonate. When the water drips from a cave ceiling, small amounts of this limestone are left behind, eventually leaving an icicle shaped stalactite. Limestone that reaches the cave floor "piles up" and forms stalagmites. Crystals are relatively uncommon in Round Spring caverns. They are produced through other chemical processes.

MATERIALS: For growing speleothems: water; thick, natural fiber string; cardboard; 2 jars; Epsom salts For crystal garden: pie tin, pieces of charcoal; 1/2 cup water; 1/2 cup salt; 1/2 cup liquid bluing; 1 cup ammonia; food coloring (do not use red); mixing bowl; spoon


Demonstration 1 - Growing Speleothems: Fill each jar with water. Add enough Epsom salts in each jar of water to form a thick solution. Place the jars on the piece of cardboard about six inches apart. Soak the string in the solution until it is completely saturated. Place one end of the string in one jar of solution. Place the other end of the string in the other jar of solution. Leave enough slack so there is a bow in the string, but do not let the string touch the cardboard. Leave the jars and the string in an accessible, and observable location for several days while a stalactite and stalagmite form. CAUTION: Once these "speleothems" begin to form, any movement of the string could cause breakage of the stalactite.

Demonstration 2 - Crystal Garden: Place several pieces of charcoal into a pie tin (enough to cover the bottom of the pan). Mix water, salt, bluing, and ammonia in the mixing bowl. Carefully pour this solution over the charcoal so that all of the pieces get wet. Squirt a few drops of food coloring over the charcoal (do not use red). Let the pan sit overnight. By the next morning, small crystals should have begun to form on the charcoal.

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Last updated: April 10, 2015

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