Minerals halite, NaCl

Salt Rock made up of the mineral halite (NaCl) formed at various periods in earth history by the evaporation of sea water. 

Put a teaspoonful of salt into a cup of water. The salt, which is made up of a great many tiny fragments of the mineral halite (NaCl), quickly disappears into the water. It is still there, of course, in some dissolved form, because the water now tastes salty, but why did it dissolve And is there any way to reverse this reaction ... 

Second, at a given saturation index, supersaturated minerals with high solubilities have the potential to precipitate in greater mass than do less soluble ones. Consider a solution equally supersaturated with respect to halite (NaCl) and gypsum (CaS04-2H20). Of the two minerals, halite is the more soluble and hence more of it must precipitate for the fluid to approach equilibrium. 

Many simple minerals, especially simple salts like halite, NaCl, sulfides, sulfosalts and oxides, have structures based upon cubic or hexagonal closest-packed arrays of either cations or anions. Coordination geometries of metal ions in many of these kinds of minerals are thus confined to more or less regular octahedra and tetrahedra. The occupancy of the two types of sites is dictated by the stoichiometry of the mineral, the radius of the ions involved and their preferred coordination geometries. Coordination of cations in mineral species in terms of bonding and crystal field effects has been extensively reviewed.16-21 Comprehensive lists of ionic radii relevant to cation coordination geometries in minerals have also been compiled.16,21... 

Salt deposits or evaporites precipitate from evaporating seawater that becomes trapped in semi-isolated marine basins. Salty desert lakes, such as Great Salt Lake, Utah, USA, or those in Death Valley, California, USA, are also sites of evaporite deposition. Common salt minerals include halite (NaCl), sylvite (KC1),... 

The ensuing suite of minerals that theoretically precipitate are, however, different for these two scenarios. For example, drying by evaporation leads to precipitation of predominantly halite (NaCl), while freezing leads to predominantly hydrohalite (NaCl-2H20) (Fig. 5.14a-b). If states of mineral hydration are preserved in ocean or lacustrine deposits on Mars, then these records could provide valuable clues to the environmental history of Mars during the drying process. 

Sufficient Na+ is now subtracted to remove all the Ch This step accounts for Cl- present in rocks as halite (NaCl), as NaCl in fluid inclusions, and as NaCl in concentrated aqueous films surrounding mineral grains in rocks. The remainder is ... 

Halite (NaCl) is a common mineral of chloride. lAAACE COPYRIGHT 2009, K MIKE. USED UNDER LICENSE FROM SHUTTERSTOCK.COM. 

However, this is not enough to condense all chlorine, which requires a 3 1 ratio of P to Cl atoms to condense all chlorine in chlorapatite. In fact, the total phosphorus abundance is too small to condense all Cl in chlorapatite. The residual chlorine, which is about 60% of total Cl, condenses as halite NaCl (420 K). However, this forms sodalite Na AlSiO Cl (405 K, and again at 315 K), which decomposes back to halite plus nepheline (365 K), over the 405 - 315 K range. Both minerals are found in chondrites. Halite is probably present in many chondrites that contain water-soluble chlorine, even though it is not reported as one of the observed minerals. 

The general formula of crystals with the halite structure is MX. The mineral halite, which names the group, is sodium chloride, NaCl, also called rock salt. 

The method can be illustrated by reference to a classical study of the defects present in iron monoxide1. Iron monoxide, often known by its mineral name of wiistite, has the halite (NaCl) structure. In the normal halite structure, there are four metal and four non-metal atoms in the unit cell, and compounds with this structure have an ideal composition MX 0, (see Chapter 1, Section 1.8). Wiistite has an oxygen-rich composition compared to the ideal formula of FeOi.o- Data for an actual sample found an oxygen iron ratio of 1.059, a density of 5728 kg m 3, and a cubic lattice parameter, a, of 0.4301 nm. Because there is more oxygen present than iron, the real composition can be obtained by assuming either that there are extra oxygen atoms in the unit cell, as interstitials, or that there are iron vacancies present. 

Soluble salts—halite (NaCl) and gypsum (CaSC>4 2H2O), as well as sulfides (pyrite, FeS2) in soils reclaimed from seas or swamps. These minerals readily dissolve in percolating water or, in the case of the sulfides, are readily attacked by oxygen. Saline and sodic ( alkali ) soils are examples of this category. 

Work on chlorine contents of coals from Illinois Basin has shown that all the chlorine present could not be accounted for in minerals present as halite (NaCl) or sylvlte (KCl) and therefore a substantial proportion is associated with the organic matter ... 

Chlorine in the earth crust is not very abimdant and it is highly dispersed. Small amounts of this element are in the composition of numerous minerals and rocks. However, main source are chlorides of alkali and alkali-earth metals, first of all halite NaCl. Rarer are potassium, calcium, magnesium chlorides bischofite, carnallite, sylvin, sylvinite, kainite and other evaporite or lake salt. The important source of chlorine in ground water is also sea water. 

Many minerals containing oxy anions, other than silicates, form primarily in sedimentary conditions that is, in aqneons solntion. Minerals containing the carbonate or sulfate ions are not likely to be formed at the high temperatures of igneous processes because both anions decompose at high temperatnres. For example, calcium carbonate decomposes to CaO and CO2. The solnbility rnles can provide a rationalization for observations such as the fact that halite (NaCl) is formed mainly in evaporated lakes with high concentrations of sodium and chloride ions, or the relatively infrequent occurrence of chal-canthite in copper mines, except where aqneons solntions may be concentrated and/or evaporated. 

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