Colorless or white when pure. Impurities produce any color but usually yellow, gray, black, brown, red (Depends on isotopes and purity for various colours)[2]
Halite (/ˈhælaɪt,ˈheɪlaɪt/HAL-yte,HAY-lyte),[7][8][9] commonly known asrock salt, is a type ofsalt, themineral (natural) form ofsodium chloride (NaCl). Halite formsisometric crystals.[10] The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on inclusion of other materials,impurities, and structural or isotopic abnormalities in the crystals.[11] It commonly occurs with otherevaporite deposit minerals such as several of thesulfates,halides, andborates. The namehalite is derived from the Ancient Greek word for "salt",ἅλς (háls).[3]
Halite cubes from the Stassfurt Potash Deposit,Saxony-Anhalt, Germany (size: 6.7 × 1.9 × 1.7 cm)
Halite dominantly occurs within sedimentary rocks where it has formed from the evaporation of seawater or salty lake water. Vast beds ofsedimentary evaporite minerals, including halite, can result from the drying up ofenclosed lakes and restricted seas. Such salt beds may be hundreds of meters thick and underlie broad areas.[12] Halite occurs at the surface today inplayas in regions where evaporation exceeds precipitation such as in the salt flats ofBadwater Basin inDeath Valley National Park.
Salt domes are verticaldiapirs or pipe-like masses of salt that have been essentially "squeezed up" from underlying salt beds by mobilization due to the weight of the overlying rock. Salt domes containanhydrite,gypsum, and nativesulfur, in addition to halite andsylvite. They are common along theGulf coasts ofTexas andLouisiana and are often associated withpetroleum deposits.Germany,Spain, theNetherlands,Denmark,Romania andIran also have salt domes.[13]Salt glaciers exist in arid Iran where the salt has broken through the surface at high elevation and flows downhill. In these cases, halite is said to be behaving like arheid.
Unusual, purple, fibrous vein-filling halite is found inFrance and a few other localities. Halite crystals termedhopper crystals appear to be "skeletons" of the typical cubes, with the edges present and stairstep depressions on, or rather in, each crystal face. In a rapidly crystallizing environment, the edges of the cubes simply grow faster than the centers. Halite crystals form very quickly in some rapidly evaporating lakes resulting in modern artifacts with a coating or encrustation of halite crystals.[14]Halite flowers are rarestalactites of curling fibers of halite that are found in certain arid caves ofAustralia'sNullarbor Plain.[15] Halite stalactites and encrustations are also reported in the Quincynative copper mine ofHancock, Michigan.
The world's largest underground salt mine is theSifto Salt Mine. It produces over 7 million tons of rock salt per year using theroom and pillar mining method. It is located half a kilometre underLake Huron inOntario, Canada.[16] In theUnited Kingdom there are three mines; the largest of these is atWinsford inCheshire, producing, on average, one million tonnes of salt per year.
Salt is used extensively in cooking as a flavor enhancer, and tocure a wide variety of foods such asbacon andfish.[17] It is frequently used in food preservation methods across various cultures. Larger pieces can be ground in asalt mill or dusted over food from a shaker as finishing salt.
Halite is also often used both residentially and municipally for managing ice. Becausebrine (a solution of water and salt) has a lower freezing point than pure water, putting salt or saltwater on ice that is below 0 °C (32 °F) will cause it to melt—this effect is calledfreezing-point depression. It is common for homeowners in cold climates to spread salt on their sidewalks and driveways after asnow storm to melt the ice. It is not necessary to use so much salt that the ice is completely melted; rather, a small amount of salt will weaken the ice so that it can be easily removed by other means. Also, many cities will spread a mixture of sand and salton roads during and after a snowstorm to improve traction. Usingsalt brine is more effective than spreading dry salt because moisture is necessary for the freezing-point depression to work and wet salt sticks to the roads better. Otherwise the salt can be wiped away by traffic.[18]
In addition to de-icing, rock salt is occasionally used in agriculture. An example of this would be inducing salt stress to suppress the growth of annual meadow grass in turf production. Other examples involve exposing weeds to salt water to dehydrate and kill them preventing them from affecting other plants. Salt is also used as a household cleaning product. Its coarse nature allows for its use in various cleaning scenarios including grease/oil removal, stain removal, dries out and hardens sticky spills for an easier clean.[citation needed]
Some cultures, especially in Africa and Brazil, prefer a wide variety of different rock salts for different dishes. Pure salt is avoided as particular colors of salt indicates the presence of different impurities. Many recipes call for particular kinds of rock salt, and imported pure salt often has impurities added to adapt to local tastes.[19]Historically, salt was used as a form of currency in barter systems and was exclusively controlled by authorities and their appointees. In some ancient civilizations the practice ofsalting the earth was done to make conquered land of an enemy infertile and inhospitable as an act of domination or spite. One biblical reference to this practice is inJudges 9:45: "he killed the people in it, pulled the wall down and sowed the site with salt."[20]
Polyhalite, a mineral fertilizer, is not an NaCl-polymer, but hydrated sulfate of potassium, calcium and magnesium (K2Ca2Mg-sulfate).
Shotgun shells containing rock salt (instead of metal pellets) are aless lethal deterrent.[21]
Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New YorkISBN0-471-80580-7
Anthony, John W; Bideaux, R.A.; Bladh, K.W.; Nicois, M.C. (1997).Handbook of Mineralogy: Halides, Hydroxides, Oxides, Mineral Data Publishing, TucsonISBN0-9622097-2-4
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