This article first appeared in Mineral News, (2016) Vol. 32, No. 10

Halite, NaCl, or common table salt, is one of the most important and ubiquitous minerals in the world, reportedly having some 14,000 industrial uses beyond its simple food applications (www.cargill.com). Despite documented occurrences at more than 1,200 worldwide localities, it is a minor also-ran among mineral collector favorites, despite its generally pleasing appearance (see figure 1) and relatively low cost.

Figure 1: A small group of cubic halite crystals from the Rhodes Salt Marsh (aka Virginia Marsh), Mineral Co., Nevada. The sample is 3cm wide; Excalibur Mineral Corp. specimen and image.

The mining of salt and its transport and trading as a valuable commodity is believed to have been established by the Bronze Age, some 5000 years ago. Its use in food preservation such as in salted meats or fish was an early application of the mineral’s ability to fight bacteria that contributed to the rotting of foodstuffs, and both brine solutions as well as caked, crystallized salt satisfied this application. Most halite deposits are formed by the evaporation of enclosed bodies of salt water, later buried by other sedimentary deposits. Widespread through many geological ages and rocks, such salt beds can range up to 1,000 feet in thickness. Subsequent deformation can result in extruded bodies of massive salt, sometimes several miles in width, occasionally poking through overlying sediments as gigantic salt domes like those in Louisiana and Texas, for example.

The largest salt domes can extend up to six miles (10 km) across and four miles (6 km) deep! In addition to acting as impermeable traps for oil and natural gas, many interesting mineral inclusions can occur (see figures 2 and 3). The salinity and temperature of formation of a salt deposit will also determine whether included calcium sulfate will occur either as anhydrite or as gypsum, and both are typical associated minerals in salt deposits. Lesser occurrences of halite include its presence as a sublimation product in volcanic regions, or as stalactitic or hair-like growths in mine workings (see figure 4). At the IMA meeting in Toronto in 1994, an excellent poster session on microscopic salt inclusions found in food-grade salt disclosed a variety of insects and insoluble minerals, some potentially deadly, accompanied by startling SEM images. I have since been suspicious of adding salt to my food.

Figure 2: (left) A pair of pseudotetragonal intergrown twins of chambersite (Mn3B7O13Cl) about 3mm across from the type locality, Barbers Hill Salt Dome, Mont Belvieu, Chambers Co., Texas. The mineral is typically found embedded in salt domes; Excalibur Mineral Corp. specimen and image.

Figure 3: (right) A pale lavender cleavage of anhydrite from the Boling Salt Dome, Newgulf, Wharton Co., Texas. Anhydrite is a common mineral inclusion in evaporite salt deposits, typically forming at higher salinity and temperatures than gypsum. Specimen is 2cm tall, Excalibur Mineral Corp. specimen and image.

The mining of salt deposits occurs both as large, underground operations (see figure 5), as well as more primitive stripping of evaporate deposits such as may occur in northeast Ethiopia and elsewhere. For significant underground deposits, traditional deep shaft mining methods such as room and pillar operations are common, the mined material used most typically for rock salt applications. Solution mining is also undertaken in many instances, usually for higher purity food use. The latter involves the drilling of multiple, connected wells, pumping water down one well to dissolve the underlying salt, and the resulting brine is then pumped to the surface and stored for subsequent processing. Brine is then pumped into huge vacuum pans, and reduced air pressure lowers the water boiling point. Application of high temperature steam boils off the water, and the process is repeated through a series of vacuum pans, producing highly refined salt.

Figure 4: (left) Stalactitic halite from Lubin, Lower Silesia, Poland. The specimen is the 3.5cm tip of a 20cm stalactite originally purchased at the Prague, Czech Republic mineral show about 20 years ago. Excalibur Mineral Corp. specimen and image.

Figure 5: (right) An early engraving of underground salt mining in Stassfurt, Saxony, Germany, extracted from the 13th edition (1885) of the German encyclopedia, Brockhaus’ Conversations-Lexikon, in this instance from one of the plates devoted to mining activities. Author’s collection.

In addition to the stripping of natural salt lakes, traditional solar evaporation of entrapped salt water deposits has been expanded and accelerated by creating artificial brine ponds. Sea water is pumped into shallow, manmade ponds, and solar evaporation slowly removes the water and ultimately produces salt beds. This technique has been in use and constantly modernized for centuries (see figure 6, below).

Figure 6: German chemist Justus Von Liebig (the mineral namee for the hydrous calcium-uranium carbonate liebigite) developed and published a method for producing a concentrated beef extract in 1847. Some fifteen years later, an investment group was formed, and with Liebig’s agreement, started a company to commercially produce his extract in Uruguay. Sold in opaque white bottles under the name Veritable Extrait de Viande Liebig (Liebig’s True Beef Extract), the thick, salty beef extract was widely used throughout Europe and the United States, recommended as a staple for soldiers during the American Civil War, and it was still in use as an Oxo bullion cube as late as WWII. In 1872, his Liebig Company (Antwerp) began to produce elaborate trading cards to popularize its brand. Those shown above depicted various aspects of salt mining and production, with the reverse side of the card offering a cooking recipe that utilized the product which contained about 4% salt. The left column cards (top to bottom) represent: a) solar evaporation ponds along the Mediterranean; b) the underground mine at Wieliczke, Poland; c) the brine cooling tower for the concentrators at Kosen, Prussia. The right column cards (top to bottom) show: a) pumping saline water from a deposit at Nauheim (Grand Duchy of Hesse); b) the evaporation works at Lunebourg in Hanover; c) the drier for salt at Lunebourg in Hanover. Author’s collection.

Major salt deposits exist throughout the world, and the U.S. is the second largest producer following China. The states of Michigan, Ohio, Pennsylvania, New York, Maine, Mississippi, Texas, Oklahoma, Utah, California, Kansas, New Mexico, Arizona and Colorado all have significant deposits. Some exploit evaporation technologies, while others employ one or both of the underground deposit mining options noted above.

In 1850, an entrepreneurial group of Quaker businessmen formed a company to exploit one such deposit in Pennsylvania, naming their concern The Pennsylvania Salt Company (see figure 7), focusing on the production of lye and other alkaline salts. Over the ensuing 100 years, The Pennsylvania Salt Company expanded into chemical manufacturing, its name changed to Pennsalt, then Pennwalt, at one point becoming the U.S. chemicals unit of Elf Aquitaine, one of the world's top 10 oil and gas companies. The Pennsylvania Salt Company also operated bituminous coal mines in Natrona, Pennsylvania, a company town it founded in the 1850s. In 1864 the company signed a contract with the Danish government to obtain cryolite from the only known site in Greenland. It had begun to use cryolite (see figure 8) as a whitener in the production of glass and ceramics. During World War II the company signed a contract with the U.S. government to manufacture synthetic cryolite for use in industrial chemical production. It is only one of many companies in the U.S. that exploited salt (see figure 9).


Figure 7: (left) Stock certificates for The Pennsylvania Salt Company are often found among scripophily enthusiasts, and they exist in a variety of colors and vintages. The pair shown here were issued in 1923 (green) and 1950 (red). Author’s collection.

Figure 8: (right) A typical example of cryolite showing sharp rhombs of siderite from Ivigtut, Greenland. The Pennsylvania Salt Company imported similar material for use as a whitener after contracting with the Danish government for its extraction and transport. The specimen is ex- A.W. Pinger (1897-1975), a Harvard-trained geologist who worked at many famous mineral localities and would later become the Chief Geologist for New Jersey Zinc at Franklin, New Jersey. Overall sample size is approximately 4.5 cm tall, Excalibur Mineral Corp. specimen and image.

Figure 9: American Potash & Chemical Corporation, headquartered in Trona, California, offered halite specimens as a marketing tool for its Searles Lake, California operations. The specimen labels were business card-sized and touted their other products. Author’s Collection.

Halite is typically colorless (see figure 10) or white, but it can take on a wide range of colors due to impurities or other causes. One particularly intriguing color is the pink halite often found at Searles Lake in California (see figure 11). The color is reportedly due to microscopic inclusions of halophilic bacteria and algae. These organisms thrive in high salt concentrations, and the name comes from the Greek word for "salt-loving".

Figure 10: (left) Halite is colorless when pure, and this sample is from Detroit, Wayne Co., Michigan, formerly in the collection of noted geologist and mineralogist E.W. Heinrich, The specimen stands 6 cm tall; Excalibur Mineral Corp. specimen and image.

Figure 11: (right) Pink halite from Searles Lake, San Bernadino, California. The color will fade over time when exposed to light, so these are best kept in the dark! Specimen size is approximately 9 x 4 cm; Excalibur Mineral Corp. specimen and image.


Figure 12: The blue color in halite has been caused by radiation damage to the mineral’s structure. This older sample is attributed to the defunct Lea Mine, 1700 level, National Potash Co., near Carlsbad, Eddy Co., New Mexico. The specimen is 3 cm tall; Excalibur Mineral Corp. specimen and image.


Figure 13: Postage stamps from Poland (left) and the former East Germany (DDR) (right) depict blue halite specimens. Many mineral collectors also pursue thematic postage stamps portraying minerals or mining activities. Author’s collection.

Perhaps the most prized color in halite specimens are delicate shades of blue or purple, the color believed to be due to structural deformities caused by radiation damage from radioactive potassium-40 found in the deposits (see figure 12). The color is so pleasing that it has even been depicted on postage stamps by a number of countries (see figure 13). Easily colored by other impurities, halite can also be orange, red, brown and a host of other shades (see figures 14 and 15). An excellent example of large inclusions of other minerals is shown in figure 16.


Figure 14: (left) A delicate peach-orange color tints this fine-grained halite specimen, likely admixed with polyhalite (K2Ca2Mg(SO4)4 • 2H2O), from the old deposit at Berchtesgaden, Bavaria, Germany. The specimen is about 7 x 6 cm; Excalibur Mineral Corp. specimen and image.

Figure 15: (right) An interesting intergrowth of halite, polyhalite and likely other salts from Hallstatt, Gmunden, Austria. The specimen is ex-Michigan College of Mines and stands 9 cm tall; Excalibur Mineral Corp. specimen and image.


Figure 16: (left) A translucent, somewhat flattened cubic crystal of halite that shows distinctive, bright white balls of included anhydrite. The specimen is from the famous Wieliczka Mine, known to have been in operation since the 13th century. The mine is no longer in operation today, but over one million people visit the Wieliczka Mine each year. The mine has dozens of statues and four large chapels carved out of the halite by the miners and local artists. The pictured specimen is about 8 x 7 cm; Excalibur Mineral Corp. specimen and image.

Figure 17: (right) This specimen is from the Salton Sea, Imperial Co., California. It shows multiple layers of growth, attesting to rising and falling water levels with evaporation occurring in a repetitious process. Running through the central portion of the specimen is a thin wooden twig, evidence of the halite growth occurring on thin, reed-like stems overhanging the water’s edge. The sample is about 6cm tall; Excalibur Mineral Corp. specimen and image.

Because of its high solubility and low temperature of formation, halite can display many interesting forms attesting to its rapid crystal growth. Hopper crystals are common, and evidence of repeated ebb and flow of solutions rich in NaCl often result in interesting and complex specimens that depict the starting and stopping of crystal growth over time, as well as showing rapid growth on foreign objects like nearby branches and twigs (see figure 17).

Halite is just one of many complex, inexpensive and diverse minerals often overlooked by collectors. Storing specimens, because of their solubility, brittleness and propensity to be highly deliquescent if there are inclusions of other chlorides, can be problematic. Many older specimens have survived well, sometimes wrapped in clear wrap or placed in plastic bags, but avoiding humidity and moisture seems to be the most important factors. Specializing in a common mineral, whether calcite, quartz, halite or another species, can bring much enjoyment and knowledge on a smaller budget.

In conclusion, as mineral prices get away from some collectors, there are ways to otherwise enjoy the hobby by extension of interest in a highly diversified and relatively inexpensive species like halite, or to items related to that species such as those illustrated in this article. Simply put: some of us will collect just about anything related to minerals or mining, and it can be done without mortgaging the farm!

SIDEBAR:

The name halite comes from the Greek word meaning salt. But the word salt is also the root for a number of other words and common expressions, some of which are presented here from Wikipedia and other sources.

Salt of the Earth: The phase is an English idiom that applies to a person who is dependable, worthy, honest and often unassuming in their demeanor. Its derivation is often ascribed to a New Testament passage (Matthew, V: 11)

Back to the Salt Mine: A phase offered with some irony that implies going or returning to work as unappealing and done with some reluctance, supposedly in allusion to the Russian practice of punishing prisoners by sending them to work in the salt mines of Siberia, equating work in general to a form of punishment.

Taken with a grain of salt: There are two schools of thought as to the origin and meaning of this idiom. On the one hand, it is suggested that the phrase implies skepticism or doubt. In this instance, it was believed to be coined by Pliny the Elder regarding the discovery of a recipe for an antidote to a poison. One of the antidote’s ingredients was a grain salt, and hence, threats involving the poison were thus to be taken "with a grain of salt", and therefore to be taken less seriously. An alternative account says that the Roman general Pompey he could make himself immune to poison by ingesting small amounts of various poisons and essentially building up an immunity to them. He supposedly took this treatment with a grain of salt to help him swallow the poison. In this version, the salt is not the antidote, but rather it was taken merely to assist in swallowing the poison.

Salting a Mine: The term “salting “ implies a trick or fraud, believed to have come from the desirability of property having a source of this valuable commodity. Crooked property sellers in Colonial times would dump salt into fresh water wells, making the property attractive to someone wanting to get into the salt business. The term soon worked its way into the modern language and applied to wells, mines etc., always implying the adding ofd something to a commodity to make it appear more valuable than it actually was.

Salary: In the Roman Empire, the soldiers serving Rome were paid with a handful of salt each day. Later, the officers in charge of distributing salt started finding the transport and preservation of the bulk material onerous, hence, the reward of salt was replaced by a sum of money allowing each man to buy his own. The money thus received was referred to as their 'salarium' (Latin) or salt-money. The term salarium entered into English which modified to modern day salary. Similarly, the Latin word salarium linked employment, salt, and soldiers, but the exact link is not very clear. This link goes back to the Roman historian Pliny the Elder, who stated as an aside in his Natural History's discussion of sea water, that "[I]n Rome. . .the soldier's pay was originally salt and the word salary derives from it...". More modern sources maintain instead that although Roman soldiers were typically paid in coin, the word salarium is derived from the word sal (salt) because at some point a soldier's salary may have been an allowance for the purchase of salt or the price of having soldiers conquer salt supplies and guard the Salt Roads (Via Salaria) that led to Rome.