The colorful stone “icicles” which hang from the roof and walls of some caves are called stalactites, and those rising from the floor are called stalagmites. Both these formations build up when water drips through rocks in a cave roof. These rocks contain mineral deposits called calcite. It is this calcite and other minerals which give stalactites and stalagmites their beautiful colors.
With each drip, the water evaporates, leaving the calcite hanging on the cave roof in an icicle like hanging, creating the stalactite. Sometimes, before evaporating, the water from stalactites drips onto the cave floor and builds a column of calcite from the floor up, creating a stalagmite.
In some cases, the stalactites and stalagmites grow to meet each other, join, and form a column.
Beautiful examples of stalactites and stalagmites can be found in Luray Caverns in Virginia, in Carlsbad Caverns in New Mexico, and in Mammoth Cave in Kentucky.
A stalactite 7-feet long took about 4,000 years to form, while larger ones have been estimated to be 200,000 years old!