What type of cave formation hangs from the ceiling?

A cave formation that hangs from the ceiling is a stalactite. Stalactites form when mineral-rich water drips through cracks in the rock above, leaving deposits behind as the water evaporates or loses dissolved carbon dioxide.

In limestone caves, the deposited mineral is usually calcium carbonate. Over long periods, repeated drips can build a thin tube, cone or more elaborate hanging shape. Stalactites are a type of speleothem, the general term for mineral deposits formed inside caves.

The matching formation on the cave floor is a stalagmite. A stalagmite grows upward where dripping water deposits minerals below. If a stalactite and stalagmite eventually join, they can form a column. Flowstone is different again: it develops as mineral-rich water spreads across a cave surface in sheets.

A useful memory aid is that stalactites hold on “tight” to the ceiling, while stalagmites might reach the ceiling. Although the classic examples are limestone formations, stalactite-like deposits can also develop from lava, mud and other materials.