Stalactites and stalagmites are formed by water dripping or flowing from fractures on the ceiling of a cave . They are the most common types of speleothems in caves. In caves, stalagmites grow rather slowly—0.00028–0.037 in/yr (0.007–0.929 mm/yr)—while in artificial tunnels and basements they grow much faster. Soda straw stalactites are the fastest growing (up to 1.57 in/yr, 40 mm/yr), but most fragile stalactites in caves. Soda straw stalactites form along a drop of water and continue growing down from the cave ceiling forming a tubular stalactite, which resembles a drinking straw in appearance. Their internal diameter is exactly equal to the diameter of the water drop. Formation of most stalactites is initiated as soda straws. If water flows on their external surface, they begin to grow in thickness and obtain a conical form. If a stalactite curves along its length, it is called a deflected stalactite. If its curving is known to be caused by air currents, it is called anemolite. Petal-shaped tubular stalactites composed of aragonite are called spathites. When some stalactites touch each other they form a drapery with a curtain-like appearance.
When a stalactite touches a stalagmite it forms a column. Usually, stalactites and stalagmites in caves are formed by calcite, less frequently by aragonite, and rarely by gypsum . Fifty-four other cave minerals are known to form rare stalactites.