• Chemistry: NaCl, Sodium Chloride • Class: Halides • Uses: Major source of salt and as mineral specimens. Halite, better known as rock salt, can easily be distinguished by its taste. Since taste is an important property of salt, there is a right way to taste a specimen of halite (or an unknown mineral that is similar to halite) and a wrong way. The right way is to first lick your index finger, rub it against the specimen and then taste the finger. This limits the amount of the mineral that actually gets in your mouth, an important consideration when you consider that there are poisonous minerals that resemble halite. Halite is found in many current evaporative deposits. It is also found in ancient bedrock all over the world where large extinct salt lakes and seas have evaporated millions of years ago, leaving thick deposits of salt behind. Perfectly formed cubes of halite are typical of the habit of this mineral. However it does form some unusual interesting habits that are much sought after by collectors. One habit is called a hopper crystal which forms what has been termed a skeleton of a crystal. Just the edges of a hopper crystal extend outward from the center of the crystal leaving hollow stair step faces between these edges. Hopper crystals form due to the disparity of growth rates between the crystal edges and the crystal faces. Often specimens are brightly colored purple and blue and with the silky luster due to the fibers, they represent a wonderful and a very uncharacteristic variety of halide. These specimens are a must have for teachers of mineral identification classes that want a stumper for those end of the session ID exams. Of course they are still easy to identify with the oft forgot simple taste test. Well crystallized specimens of halite cubes can be very impressive and popular. Some are colored an attractive pastel pink by inclusions of bacterial debris that are trapped during crystallization in an evaporative lake. Often these specimens that are sold world wide in rock shops and in mineral shows where grown within the past year. In fact, the crystals form so fast and so well in some evaporative lakes that mineral dealers are using their imaginations to enhance their inventory. They are putting sticks, animal skulls and other imaginative items into these lakes and retrieving them a relatively short time later covered in clusters of white or pink halite cubes. Halite is a soft mineral that flows easily under pressure. At depths of as little as 3 kilometers, it begins to rise through the rocks above it in cylindrical plugs called salt domes. These are of interest to oil prospectors because petroleum collects around them.
Halite (sodium chloride) comes from the Greek halos, meaning "salt" and lithos meaning "rock," and is in fact, better known as rock salt. Halite is called evaporate because it is formed by the evaporation of saline water in partially enclosed basins. It is very common worldwide, deposited in solid underground masses, and as a dissolved solution in oceans and many arid-region inland lakes. Huge Halite deposits are mined for common table salt (NaCl), which is in great demand and has many uses, including: • food seasoning • for road safety in the winter months to melt snow and ice • as salt licks for cattle to provide them with essential salt • for water softeners • for medicinal purposes • primary ore for both sodium and chlorine Halite is extremely common. It is found in solid masses, and as a dissolved solution in the oceans and many inland lakes. The inland lakes that are rich in salt exist in arid regions, and are commonly below sea level without an outlet. In many of them there is more water being evaporated than the amount coming in, causing a recede in the water level of the lake and an increase of salinity content. This has only recently become an issue, for much of the tributaries to the lakes have running water which is partially drained for human usage. As the water evaporates, chunks of salt are leftover on the shores of the lake. The water levels can be extremely high in salt content, and a stick or stone placed in the water will become coated with a layer of Halite if allowed to form. Many of these inland lakes have already dried up, leaving over enormous salt deposits which are commercially mined. Halite also exists in non-arid regions. It is only possible for it to exist in underground deposits, for anything on the surface would dissolve from rainwater. Enormous deposits exist underground in certain areas, reaching great depths. These deposits are mined by drilling wells into the salt layer, and bringing in hot water which quickly dissolves the salt. The water becomes saturated with dissolved salt (the solution is known as "brine") and is then pumped out. The brine evaporates and the remainder is mostly salt, which is refined and then put to use. Hopper shaped cubes may result when the brine is evaporated. Halite is mined by shaft mining or by pumping water into the deposit and later pumping out the brine. In purification, potassium, and magnesium salts, bromine, and iodine are obtained as by-products. The halite is recrystallized, becoming very pure in the process. In addition to its use in food and as a preservative, salt is essential in chemical industries, in the manufacture of soda ash for glass products, and in soap making and metallurgy. Chlorine from salt is used as bleach and in water purification.
When halite occurs in non-arid regions, it is only possible for it to exist in underground deposits, for anything on the surface would dissolve from rainwater. Indeed, a great deal of halite is found in ancient bedrock all over the world where large extinct salt lakes and seas evaporated millions of years ago, leaving behind thick deposits of salt in beds that range from a few feet to more than 1,000 feet in thickness. These deposits are mined by drilling wells into the salt layer, and pumping hot water to quickly dissolve the salt. When the water becomes saturated with dissolved salt (the solution is known as "brine"), it is pumped out. When the brine evaporates, the remainder is primarily sodium chloride, which is refined and utilized.
Inland lakes that are rich in salt exist in many arid regions, especially in the Deserts. They usually have no outlet, and are often below sea level. In such lakes there is more water being evaporated than the amount entering, causing the volume of water to decrease, while increasing its salinity. In some lakes, concentrations of salt brine can become so extreme that a stick or stone placed in the water will become coated with a layer of Halite. As the water evaporates, the shoreline recedes and chunks of salt are left crystallized on the beaches. Many of these inland lakes have already dried up completely, leaving enormous salt deposits that are commercially mined.
Well crystallized specimens of halite cubes are very impressive and quite popular with rockhounds. Halite crystals form so fast and so well in some evaporative lakes that many such specimens that are sold worldwide in rock shops and at mineral shows were grown within the past year Some halite crystals are colored pinkish by bacterial debris trapped during crystallization while others are colored bright purple or blue, with a silky luster. Halite also forms some unusual variations that are prized by collectors. One variation, called a hopper crystal, forms what has been termed a skeleton of a crystal. Just the edges of a hopper crystal extend outward from the center; leaving hollow stair step faces between these edges. Hopper crystals form due to the disparity of growth rates between the crystal edges and the crystal faces. Since taste is an important property of salt, taste is one of the important means of identifying this mineral. The correct way to taste a mineral specimen is to first lick your index finger, rub it against the specimen and then taste the finger. Remember that there are poisonous minerals that resemble halite. Hydro halite is not strictly a variety of Halite, but a very rare, similar mineral with the formula NaCl + 2H2O. This variation forms only under very unique conditions where the water does not dissolve the salt and becomes an integral part of the structure of the mineral.
Hardness 2 Specific gravity 2.1+ (light) Cleavage Perfect in three directions forming cubes. Color Clear or white but can be found blue, purple, pink, yellow and gray. Fracture Conchoida Crystal Habits Predominantly cubes and in massive sedimentary beds, but also granular, fibrous and compact. Some crystals show a crystal type called a hopper crystal described above. Luster Vitreous Streak White. Transparency crystals Crystals are transparent to translucent Crystal System Isometric; 4/m bar 3 2/m Characteristics Salty taste Associated Minerals include Other evaporate deposit minerals such as several sulfates, halides and borates. Best Field Indicators Taste, cleavage and crystal habit
Chemical Formula NaCl Composition Sodium Chloride Color Colorless, white, red, yellow, orange, pink, green, blue, violet, gray Streak White Hardness 2 - 2½ Crystal Forms and Aggregates (Isometric) Crystals occur as cubes, often distorted with hopper growth. Rarely occurs in octahedrons. Normally occurs massive, grainy, and incrusting. Large cubic chunks often break apart into cubic cleavage fragments. Transparency Transparent to translucent Specific Gravity 2.1 – 2.6 Luster Vitreous Cleavage 1, all sides – cubic Fracture Conchoidal Tenacity Brittle Other ID Marks 1) Sharp salt taste 2) Soluble in water 3) Some specimens fluoresce, usually red Other Names Salt, Common Salt, Natural Salt
Halite is the source of common salt. Enormous Halite deposits are worked for salt. Salt has many uses, and must be heavily mined to satisfy demand. Some of its most famous uses are: • as food seasoning • for road safety to melt snow and ice • as salt licks for cattle (these provide the cattle with salt, which is essential to their health) • For chemical purposes • Halite is also the most important ore of both sodium and chlorine.