Rock salt is a chemical sedimentary rock that forms by the evaporation of water (usually seawater) and the precipitation of dissolved minerals.  Chemical sedimentary rocks that form by the evaporation of water are called evaporites.  Rock salt & rock gypsum are the two most common evaporites.


Rock salt is composed of the mineral halite (NaCl - sodium chloride).  It ranges in color from clearish to grayish to orangish-brown, but sometimes has other colors, such as blue.  It has a strongly salty taste, is often coarsely-crystalline, and is relatively soft (H = 2.5).


Rock salt is also known as halitite, which refers to sedimentary evaporite deposits composed of halite (NaCl).  Halitite has also been used in the geologic literature to refer specifically to rock salt that's been contact metamorphosed by igneous intrusions.



Rock salt (halitite)



Rock salt (halitite)



Rock salt (halitite)



Rock salt (halitite) (8.3 cm across) - blue & whitish & clear & orangish rock salt (8.3 cm across) from the subsurface Salado Formation of New Mexico.  The orangish and bluish coloration is caused by radiation from potassium-40 in nearby potash salts, resulting in excess free sodium metal in the halite.

Stratigraphy: McNutt Member (McNutt Potash Member), middle Salado Formation, Ochoan Stage, upper Upper Permian.

Locality: Mississippi Potash East Mine, Carlsbad Potash District, Eddy County, southeastern New Mexico, USA.



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