Caverns form when acidic water dissolves limestone rock.
Caverns are an interesting geological phenomenon. Most caverns form by the dissolution of limestone rock in the subsurface. The calcite, a main component of limestone, dissolves in acidic water formed by the contact of water and carbon dioxide in the atmosphere and soil. These solution caverns form when the acidic water begins to dissolve the limestone around the depth of the water table. As the water table elevation fluctuates over time, the cavern enlarges and forms unique features such as stalactites, stalagmites and groups of perfect crystals.
Growing Stalactites and Stalagmites
Stalactites and stalagmites are cavern formations where the crystal forms icicle shapes from the top and bottom of the cavern, respectively. These pillars form through precipitation of calcite crystals. You can recreate this type of crystallization through a simple science experiment. You will need two identical glasses or jars, Epsom salts, water, a saucepan, stirring spoon, cotton string and paper clips. To create the salt solution, fill the glasses or jars with water, then transfer the water to the saucepan. Heat the water until it is very hot but not boiling. Slowly dissolve Epsom salts into the water until the solution is saturated and no more salt will dissolve and begins to settle to the bottom of the saucepan. Pour half of the solution into each glass or jar and set them about 4 to 6 inches apart on a counter. Cut a length of the string and tie a paper clip to each end. Sink one end of the string to the bottom of each glass or jar and allow the string to sag slightly between the glasses. Allow the experiment to sit for several days and watch stalactites and stalagmites form between the glasses through precipitation from the string. This project is appropriate for school-age children, although adults should supervise young children when they make the solution.
Dissolution Experiment
Caverns form from limestone rocks, which are mostly calcite. The acid content of the water below ground dissolves the limestone because of the calcite content. You can design a science experiment to help children see how acid dissolves calcite and at the same time, they can use the experiment to help them understand what calcite and limestone look like and identify them. Gather a group of samples for this project that includes calcite, limestone and a variety of non-calcite containing minerals or rocks. Place drops of acid on each sample and observe their reaction. Calcite and rocks containing calcite will fizz or bubble the acid. The fizz is the calcite dissolving. You can adjust this project for children of different ages. High school students can use dilute hydrochloric acid, with proper safety equipment, while younger children can use lemon juice or vinegar, which is a much weaker acid. If you are using a weak acid, you may need to observe the reaction through a hand magnifier to see the reaction.
Crystal Formation by Evaporation
Inside a cavern, mineral crystals may form through evaporation. You can recreate this phenomenon using a solution of baking soda and water. To create the solution, mix baking soda into a jar of water and stir to dissolve and fully mix the solution. You should stop adding baking soda when it no longer dissolves into the water and begins to fall to the bottom of the jar. Put the jar in a warm location and allow the water to evaporate. This science project will take several days to complete as the water slowly evaporates from the jar. Ask children to measure the water level daily to determine if the water is evaporating at a steady rate. As the water disappears, crystals will remain in the jar, similar to a natural cave. You can also perform this science project with a saltwater solution.
Crystal Formation by Precipitation
Chemical precipitation inside a cavern can form large, distinct crystals along the cave walls. You can use a sugar solution to form precipitation crystals in a similar manner. To conduct this science experiment, boil 1 to 2 cups of water in a saucepan and slowly add 2 to 4 cups of sugar, 1 tablespoon at a time, allowing the sugar to dissolve between each addition. When the sugar no longer dissolves, pour the solution into a clean glass jar. Suspend a cotton string into the jar but do not let the string touch the sides of the jar. Over a few days, sugar crystals will grow along the string through precipitation from the solution. The longer the solution sits undisturbed, the larger the sugar crystals will grow. Children enjoy this science project because it teaches them about how individual crystals can form in a cave. It also makes a sweet treat.
Tags: acidic water, baking soda, crystals will, into water, science experiment
