The wind direction changes as often as the weather conditions outside change. But the dripstones grow very slowly – several centimeters in 100 years – meaning that 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 idea is that many caves with helictites have no natural entrance where wind could enter. Piezoelectric forces Another hypothesis that has been proposed is that slowly changing geological pressure causing stresses on the crystals at the base alters the piezo electrostatic potential and causes particle deposition to be oriented in some relationship to the prevailing pressure orientation. Bacterial A recent hypothesis, which is supported by observation, is that a prokaryotic bacterial film provides a nucleation site for mineralization process. Helictite growth A helictite starts its growth as a tiny stalactite. 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. For an unknown reason, when the chemical composition of the water is slightly altered, the single crystal structure can change from a cylindrical shape to a conical one. In some of these cases, each crystal fits into the prior one like an inverted stack of ice cream cones. See also Anthodite References External links The Virtual Cave: Helictites Microbial mediation of complex subterranean mineral structures The Virtual Cave: Helictites Helictite or Eccentric? Does crystal splitting play a part in the curvature of helictites? (Abstract) By George W. Moore, Journal of Cave and Karst Studies, v. 62, p. 37 (2000). Speleothems