Efflorescence, also known as salt frost, is composed of white soluble mineral salts that form on the ground surface, shallow soil, sinter and rock surfaces in hot spring areas. The mineral compositions of efflorescence include halite (e.g., rock salt), sulphate (e.g., alunogen, alunite, mirabilite and epsomite), boric acid (borax and kernite) and carbonate (e.g., trona). Efflorescence looks like fluff, a thin shell, a ring, or can be stacked to form a cactus shape. It can also stick to a wall like hanging stalactites. It is the product of the evaporation of hot springs or the capillary effect in soil layers in springs. The efflorescence in some hydrothermal zones can become mineral resources.