Stalactites are basically icicles of rock that form in moist cave environments.
A stalactite is a formation of mineralized water that appears in humid environments in caves. More classically, stalactites are made of calcium carbonate, although they can also contain other minerals, which can make these rock icicles look veined with intense colors. Many caves around the world have impressive stalactite formations that are quite interesting to visit; if you’re passionate about seeing some giant stalactites, Doolin Cave in Ireland and Jeita Cave in Lebanon have some particularly good examples.
Unlike stalactites, stalagmites are completely solid and grow on the floor of a cave.
These unique formations occur in wet caves, where the water becomes mineralized as it slowly flows through the rock that forms the cave. As the water makes its way into the air, it evaporates, leaving behind a small deposit of calcium carbonate and other minerals. Over time, the deposit turns into what is known as lime or soda straw, a hollow formation that hangs from the ceiling. The edges of the straw also begin to form, forming the familiar elongated conical shape of a stalactite.
In cross section, a stalactite has a hollow core where the soda straw used to be. Scientists have also found that stalactites have very regular shapes that appear to be mathematically predictable. Researchers at the University of Arizona in 2004 found that stalactites actually have the same shape, no matter how big they are; the shape is really just a matter of magnification.
Where you find stalactites, you can also sometimes find stalagmites, conical formations that grow from the floor of a cave rather than the ceiling. Stalagmites are solid rather than hollow, and in situations where they grow into a descending stalactite, the two formations can merge and form a column. Many people have trouble remembering which is which. It may be helpful to remember a little play on words: stalactites “seep tight” from the ceiling, while “mighty” stalagmites do not have a central hollow space.
A large stalactite can take a long time to form. Therefore, you should resist the temptation to break the stalactites as a souvenir, as they will take centuries to grow back. In some areas, it is also not legal to remove anything from regional parks and reserves, to ensure that wonderful sights such as stalactites are always available for people to enjoy.