rock salt

noun

Etymology: From rock + salt.

1. The mineral halite.

   “Farther to the southward, the rivers which are affluent to the Colorado, such as the Rio Virgen, and Gila river, near their mouths, are impregnated with salt by the cliffs of rock salt between which they pass.”

2. Coarsely ground common salt, often used as road salt, as feedstock, or for other applications.
3. Synonym of sea salt, due to its rocky texture.