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Cave formations are called speleothem, from the Greek word spelaion, cave and thema meaning deposit. Almost all of them are made of calcite, the crystal of calcium carbonate. Different minerals and different movements in the water account for an incredible variety of cave formations.
Erosional caves can be found in almost any kind of rock, from hard granite to soft claystones, and even including limestone. In fact erosion can be a very active process in caves originally formed by solution caves as well, but usually occurs after the cave has drained and surface streams are pirated into the cave. Erosion tends to produce tall, canyon-like passages. Running water on glaciers may sink into crevasses and melt a path through the glacier to form glacier caves. These often show pronounced scalloping on the walls and ceilings, and are often decorated with ice formations.