A speleothem which changes its axis from the vertical at one or more stages of its growth. Helictites have a curving or angular form that looks like they had grown in zero gravity.
The growth of helictites is still very enigmatic. Until now there is absolutely no explanation for how they formed.
One theory blames the wind in the cave as main reason for the strange look. Drops hanging on a Stalactite are blown to one side, so the dripstone grows into this direction. If the wind changes, the direction of growth changes too.
This theory is very problematic, because wind directions change very often. The wind in caves depends on air pressure changes outside depending on the weather (see Wind Cave). So the wind direction changes as often as the weather conditions change. But the dripstones grow very slow, several centimeters in 100 years. So the direction would change every milimeter.
A second problem with this theory is, that many caves with helictites never had an natural entrance.
Another theory blames capillary forces. If the helictite has a very thin central tube where the water flows like in straws, capillary forces would be able to transport water ignoring gravity. This was inspired by some hollow helictites.
The problem with this theory is, that most helictites are definitely not hollow.
The way helictites are formed is still unknown. This is definitely the most interesting problem in speleologie.