Helictites

Helictites are contorted depositional speleothems which grow in any direction, defying gravity. Some geologists use a fancier term, “non-gravitomorphic”. They occur in many forms from tiny filaments (photo #1) through to thick, antler-like forms (photo #6). The intervening photos try to show a progression of thicker threads.

Most helictites are formed from calcite, but can be composed of aragonite as well.

Helictites are formed by calcite-laden waters seeping through tiny pores in the rock. Hydrostatic pressure forces a small amount of the solution out, carbon dioxide is lost, and calcite is deposited. Growth continues through a tiny, central capillary chanel, which the solution flows through via hydrostatic and capillary pressure to emerge and deposit calcite at the tip. In higher flow conditions it can come out the tip and travel back along the length of the helictite, making it thicker.

Helictites are a very diverse group of speleothems, likely because different factors influence them, as noted below. They are not rare, but extensive displays of them are. One show cave in California, Black Chasm Cavern, was designated a National Natural Landmark because of its profuse displays of translucent helictites (photos 9 and 10). There is also an even rarer category that forms underwater, best known from Lechuguilla Cave, New Mexico (photo #11) . These grow where drip water with dissolved gypsum content mixes with calcite laden water and precipitates the crystals, which tend to be very fine and delicate, like a fine angel pasta.

The twisted shapes are due to many factors, including:

(1) impurities in the deposited calcite

(2) wedge-shaped crystals causing uneven deposition

(3) plugging of the central channel may occur in dry periods, and when flow resumes, the pressure may force a new channel out the side of the original one

(4) air currents may favor growth in a particular direction. Sometimes helictites are found facing the same direction down a passage (as in photos 7 and 8).