A stalactite is a mineralized water formation which arises in moist cave environments. Most classically, stalactites are made from calcium carbonate, although they may contain other minerals as well, which can cause these icicles of rock to be streaked with rich colors. Many caves around the world have stunning stalactite formations which are quite interesting to visit; if you have a passion to see some gigantic stalactites, Doolin Cave in Ireland and Jeita Cavern in Lebanon have some particularly fine examples.
These unique formations occur in moist caverns where water becomes mineralized as it flows slowly through the rock which makes up the cave. As the water forces its way out into the air, it evaporates, leaving behind a small deposit of calcium carbonate and other minerals. Over time, the deposit builds into what is known as a lime or soda straw, a hollow formation which dangles from the ceiling. The edges of the straw start to build up as well, ultimately forming the familiar elongated conical shape of a stalactite.
In cross-section, a stalactite has a hollow core where the soda straw once was. Scientists have also discovered that stalactites have very regular shapes which appear to be mathematically predictable. Researchers at the University of Arizona in 2004 learned that stalactites actually have the same shape, no matter what size they are; the shape is really just a question of magnification.
Where you find stalactites, you can also sometimes find stalagmites, conical formations which grow up from the floor of a cave, rather than from the ceiling. Stalagmites are solid, rather than hollow, and in situations where they grow up towards a descending stalactite, the two formations can fuse together and form a column. Many people have difficulty remembering which is which. It may be helpful to remember a little play on words: stalactites “hang tight” from the ceiling, while “mighty” stalagmites have no hollow central space.
A big stalactite can take a very long time to form. For this reason, you should resist the temptation to break off stalactites as souvenirs, since they will take centuries to regrow. In some areas, it is also not legal to take anything out of regional parks and preserves, to ensure that delightful sights like stalactites will always be there for people to enjoy.