Grade Level: Modify for all ages
Source: National Park Service
Caves are naturally occuring underground cavities large enough for human entry. Caves contain a large number of minerals, of which calcite is one of the most common minerals. Speleothems, often called cave formations, are formed as rainwater passes through the soil and absorbs carbon dioxide. As water and carbon dioxide mix it forms a weak acid called carbonic acid, which helps to dissolve underlying rock. When water seeps into the air-filled cave it loses carbon dioxide to the cave atmosphere causing the water to precipitate calcite deposits in different forms. Calcite precipitates on ceilings, walls, and floors as speleothems.
There are many types of speleothems, but the most common that people are familiar with are stalactites and stalagmites. Stalactites are formed by mineral rich dripping water and they grow down from the ceiling like icicles. Stalagmites are formed when mineral rich water drops from stalactites and accumulates on the cave floor, growing upward like a cone. Sometimes a stalactite and stalagmite grow together to form a column.
- 1 small plate/saucer, or piece of aluminum foil
- 1 spoon
- 2 paper clips
- 2 jars of the same volume/size
- Epsom salt
- Hot water
- Thick cotton string or yarn (natural fibers)