Stalagmite in Rock Crystal from Mongolia (new site in 2016)

A stalactite (UK /ˈstæləktaɪt/, US /stəˈlæktaɪt/; 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

A stalagmite (UK /ˈstæləɡmaɪt/ or US /stəˈlæɡmaɪt/; from the Greek σταλαγμίτης - stalagmitês, from σταλαγμίας - stalagmias, "dropping, trickling") is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites may be composed of amberat, lava, minerals, mud, peat, pitch, sand, and sinter.The corresponding formation hanging down from the ceiling of a cave is a stalactite. Mnemonics have been developed for which word refers to which type of formation; one is that stalactite has a C for "ceiling", and stalagmite has a G for "ground"