Stalactites are mineral formations that hang from the ceilings of caves. They are created by the slow dripping of mineral-rich water, which leaves behind deposits as it evaporates. Over time, these deposits accumulate and form icicle-like structures that can vary in size and shape. These formations are primarily made of calcium carbonate, which is derived from limestone rock. Stalactites grow very slowly, often taking thousands of years to develop just a few inches. They are commonly found in limestone caves, where the right conditions for mineral deposition exist.