helictite, cave deposit that has a branching, curved, or spiralled shape and may grow in any direction in seeming defiance of gravity. A helictite begins as a soda-straw-like tube formed as individual drops of water deposit calcium carbonate around the rim. The drops do not fall as in stalactite formation but evaporate in place. The direction of growth is thought to be determined by the chance orientation of crystal axes of the calcite carried in the water.