Caves are full of mineral deposits that form unique shapes, such as the icicle-like stalactites (which hang from the ceiling) and stalagmites (which rise up from the ground). (To learn more about cave rock formations, go to our Stalactites, Stalagmites, & Other Cave Formations Teaching Tip.) Make your own stalactites and stalagmites with this project! (Adult supervision recommended.)
Cut two 24' pieces of cotton string or wool yarn, and tie one metal washer to each end to act as a weight.
Fill four small glass jars or beakers 2/3 full with very warm (120-140 °F) water. Stir in as much baking soda into two of the jars as will dissolve; do the same with Epsom salt in the other two jars. Put the jars in a warm place where they can sit undisturbed for about a week.
Next, place a small plate between each set of jars and put the ends of one string in the baking soda jars with the middle of the string draping in a 'u' shape just above the plate. Do the same with the Epsom salt.
After a few days, check to see if any material has built up on the string. An icicle-like formation should form downward on the string and upward on the plate. Real stalagmites and stalactites are formed in almost the same way, by mineral-containing waters dripping in caves until a deposit of calcium carbonate builds up...or down, as the case may be.