Photo of glass stalactite in the Florida Aquarium gift shop (2014).
A stalactite (UK //, US //; from the Greek stalasso, (σταλάσσω), “to drip”, and meaning “that which drips”) is a type of formation that hangs from the ceiling of caves, hot springs, or manmade structures such as bridges and mines. Any material which is soluble, can be deposited as a colloid, or is in suspension, or is capable of being melted, may form a stalactite. Stalactites may be composed of amberat, lava, minerals, mud, peat, pitch, sand, and sinter. A stalactite is not necessarily a speleothem, though speleothems are the most common form of stalactite because of the abundance of limestone caves.
The corresponding formation on the floor of the cave is known as a stalagmite.
Stalactites are first mentioned (though not by name) by the Roman natural historian Pliny in a text which also mentions stalagmites and columns and refers to their creation by the dripping of water. The term “stalactite” was coined in the 17th century by the Danish Physician Ole Worm, who coined the Latin word from the Greek word σταλακτός (stalaktos, “dripping”) and the Greek suffix -ίτης (-ites, connected with or belonging to)