Halite macrocrystalline stalactites of the Atacama caves (Chile).

Interesting salt caves were recently discovered in one of the driest places on earth, the Atacama desert (Chile). The caves, sometimes over 1 km long, host important and widespread active halite speleothems among which peculiar macrocrystalline stalactites, which are here described for the first time. The macrocrystalline stalactites consist of a sequence of interpenetrated halite cubes, often with a hopper structure; the halite cubes are always oriented with the long diagonals coincident with the speleothem elongation axis. A few of these stalactites exhibit a perfectly vertical structure, while most of these speleothems are inclined (with a deviation from the verticality up to 30-40 degrees). Internal feeding tubes are completely absent. The evolution of these speleothems is induced only by condensation/evaporation processes. While the feeding of these speleothems is always related to condensation processes, their evolution is controlled by several interconnected factors: 1- air current distribution close to the speleothems; 2 - condensation and evaporation processes and 3- capillary, and/or gravitational movements of the solution along the speleothems. In many cases these factors allow for the development of exasperated hopper structures, giving rise to wide rectangular thin flat tabular crystals. Finally in a single location, peculiar bidimensional pyramidal structures of halite crystals have developed where the gravitational flow of the feeding solutions meets a strong upward air flow. Keywords: Halite, macro-crystalline speleothems, genetic mechanisms