Helictite

A helictite is a speleothem found in limestone caves that changes its axis from the vertical at one or more stages during its growth. They have a curving or angular form that looks like they had grown in zero gravity.

Helictites are, perhaps, the most delicate and most beautiful of cave formations. They are usually made of calcite, needle-form calcite and aragonite. Forms of helictites have been described in several types: ribbon helictites, saws, rods, butterflies, "hands", curly-fries, and "clumps of worms." Typically the helictite has radial symmetry.

Formation

The growth of helictites is still very enigmatic. Until now there has been no explanation for how they formed, and even now there are only theories.

One theory names the wind in the cave as main reason for the strange look. Drops hanging on a stalactites are blown to one side, so the dripstone grows in that direction. If the wind changes, the direction of growth changes too. However this theory is very problematic, because wind directions change very often. The wind in caves depends on air pressure changes outside, which in turn depend on the weather. Wind caves are known to experience these windy conditions. The wind direction changes as often as the weather conditions outside change. But the dripstones grow very slow, several centimeters in 100 years, meaning the wind direction would have to stay steady for long periods of time, changing for every fragment of a millimeter of growth. A second problem with this theory is that many caves with helictites have no natural entrance where wind could enter.

Another theory explains helictites with 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 theory was inspired by some hollow helictites. However, the problem with this theory is that the majority of helictites are definitely not hollow.

A helictite starts its growth as a tiny stalactite. For an unknown reason the chemical composition of the water is slightly altered causing the single crystal structure to change from a cylindrical shape to a conical one. Sometimes each crystal fits into the prior one like an inverted stack of ice cream cones. The direction of the end of the straw may wander, twist like a corkscrew, or the main part may form normally while small helictites pop out of its side like rootlets or fishhooks. In some caves, helictites cluster together and form bushes as large as six feet tall. These bushes grow from the floor of the cave. When helictites are found on cave floors, they are referred to as heligmites, though there is debate as to whether this is a genuine subcategory.

History

The first detailed description of helictites was made in 1665 by Olaus Worm.