Halite

Mineral Name: Halite

Other names of mineral: Halite is also called Natrikalite, Rock Salt, Muriate of Soda

Chemical Composition: NaCl, Sodium Chloride

Color: Colorless, white, blue, red, pink, yellow, orange, green, and gray. The wide color spectrum of halite specimens are the result of exposure to impurities in the environment where they formed, such as algae.

Streak: Colorless.

Hardness: 2.5

Cleavage/Fracture: Halite has 3 planes of cleavage, perfect in three directions forming cubes. It's fracture is conchoidal. Halite is generally very cubic in appearance, it’s cleavage is very easy to see.

Crystal Form: Generally cubic form, can rarely be octahedral. Halite’s crystal faces are often cavernous and stepped, resembling stairs (3).

Luster: Vitreous to greasy.

Special Features: Halite has a salty taste, is soluble in water, and has some specimens that fluoresce in long-wave ultraviolet light.

Varieties: Halite varieties include rock salt and hydrohalite.

Mineral Group: Halite belongs to the mineral group of the Halides or Halogenides. Halides, along with borates and nitrogens, are minerals that combine with the halogen elements, boron and nitrogen. Beside halite, other examples include fluorite, sylvite, and borax (4). Halite is also an evaporite. Evaporites are sediments that are created chemically by the evaporation of an aqueous solution. Common evaporites include halite, gypsum and calcite (5).

Environment: Halite forms in environments that include the edges of salt lakes, dry lakes, sedimentary salt beds, and salt domes (3). When deformation occurs in underground halite deposits this can sometimes cause aboveground extrusions of salt, resulting in formations such as the salt domes in areas certain of Texas, and salt glaciers like those in the Zagros Mountains (5). Saline-rich lakes in arid inland regions are the most common environment for halite forming above ground. These types of lakes usually have no outlet, such as the Great Salt Lake of Utah. Halite occurs in lakes like these because the amount of water being evaporated exceeds the amount of new water entering the environment, causing a lower volume of water and a higher salinity content (5). Halite can also be easily grown artificially.

Associated Rock types: The most common rock type associated with halite is rock salt. Associated rock types include other evaporite deposit minerals such as several sulfates, borates and halides. Associated minerals include gypsum, borax and sylvite (3).

Occurrence in North America: Halite can form in multiple ways, as a result it can be found throughout North America. The cities of Detroit and Cleveland both rest atop huge halite deposits that are mined for road salting (3). Searles Lake, California and large portions of Utah produce huge quantities of halite as well (3).

Economic Uses: Food preservation and seasoning are the two most common economic uses of halite, though it has many others. Salt dries out the food by absorbing large quantities of the water contained in the food. When all of the water is gone, the food will take longer to spoil because there is a less conducive environment for bacteria or mold to grow and begin the decomposition process. Ancient Ethiopia, Ancient Greece and Ancient Rome utilized salt bars and disks as forms of currency and payment (7). Notably, Ancient Rome would often pay soldiers in salt, which is where the word ‘salary’ is derived from (6.) Halite can also be used in the treatment of some medical ailments such as cold and congestion symptoms, and also in the treatment of thrush (1).

Industrial Uses: Crushed halite is used as a winter road treatment when salting roads to melt the ice and snow. Halite helps to melt the existing ice on the roads, the salt dissolves into the water in the ice and lowers its overall freezing point by mixing with existing liquid water in the ice.

Halite is used widely in the chemical industry, a few of its applications in the chemical industry include pharmaceuticals, glassmaking, waste and water treatment, and textiles (2). Human consumption of salt accounts for only a small percentage of its total use, with over two thirds of its consumption being funneled into winter road salting and the chemical industry (2). Salt is also used in the water softening process. Hard water is water that contains Ca and/or Mg. Due to the way that these ions react with detergents, they weaken any cleaning agent, making it challenging to remove scum and grungy buildup. Hard water is what leaves a residue in your tub or sink, on your dishes and even in your hair. To soften the water, you can use an ion exchange device that contains halite. Inside of this device, as the hard water passes through, the sodium ions are exchanged for the hard water ions (9).

First Notable Identification: The mineral name for sat was given by E.F Glocker in 1847 (8). Humans utilizing and cultivating salt is an ancient practice that can be observed in many cultures and civilizations throughout the historical and archaeological records. The earliest known occurrence of salt harvesting is thought to have been at Lake Yuncheng, in the Chinese province of Shanxi at approximately 6000 B.C.E. (6). However, the first usage of halite could have been much earlier in time and there could simply be no evidence of it occurring earlier in the record (6).

How We Identified It: Halite is the natural mineral form of salt, so licking it is possible in order to help identify it quickly (though this is highly discouraged unless it has already been identified as halite). It’s cleavage (three planes at right angles) and hardness (2.5) are two other easy ways to identify it.

Don’t Confuse It With: Quartz and Calcite. Quartz is much harder, 7, compared to halite. Calcite is slightly harder than halite and takes on a rhombus shape, as opposed to halite’s cubic shape.