A stalactite or dripstone, is a type of speleothem that hangs from the ceiling or wall of limestone caves.
Stalactites come in a variety of forms, some of which have their own classification, such as deflected stalactites. Another much rarer form is the elephant's foot stalactite, which is flat, rather than pointed, on the bottom. An image of these is in the lower table, second image from the left
Stalactites appear in many caves or caverns. The Carlsbad Caverns in New Mexico, is made up of limestone, which is a fairly soft rock that can be dissolved by a weak acid. The acid that dissolves limestone comes from the rainwater. These raindrops combine with the carbondioxide from the air and the soil, and thus changes into carbonic acid.
About one million years ago, the rainwater dripped into the ceiling of the caves, they formed, tiny rings of lime, which crystallized in the ceiling. As time passed, these rings of lime formed a little stone "icicle". It kept on growing. As the time passed, thousands of drops fell on the same spot. The specks of lime formed, looked like a stubby stone candle. The "candle" kept on growing.
The icicle of stone on the ceiling is called a stalactite. The stubby candle on the floor is a stalagmite. Each stalactite and stalagmite grows at a different rate, depending on the wetness of the cave, the temperature of the room, and the thickness of the limestone bed above it.