Cave formations like stalactites and stalagmites, collectively known as speleothems, form as water seeps through limestone. As the water moves through the rock, it dissolves small amounts of limestone also called calcium carbonate. When the water drips from a cave ceiling, small amounts of the mineral calcite (also called calcium carbonate) are left behind, eventually leaving an icicle shaped stalactite; water droplets that fall to the cave floor deposit calcite to form stalagmites. Following the instructions below will allow you to simulate and observe how a speleothem forms in a cave using water and the mineral salt.