| Evaporite |
Articles about Evaporite |
Information AboutEvaporite |
| CATEGORIES ABOUT EVAPORITE | |
| sedimentary rocks | |
| mineralogy | |
|
FORMATION OF EVAPORITE ROCKS Evaporites are formed by evaporation of restricted bodies of water at the Earth's surface. Although all water bodies on the surface and in aquifers contain dissolved salts, in order to form minerals from these salts, the water must evaporate into the atmosphere in order to precipitate the minerals. In order for this to happen the water body must enter a restricted environment where water input into this environment remains below the net rate of evaporation. This is usually an arid environment with a small basin fed by a limited input of water. Most evaporites are derived from bodies of sea-water, however evaporites can be created by evaporation of fresh water sources such as rivers, by aquifers or even by rainfall. EVAPORITE DEPOSITIONAL ENVIRONMENTS Evaporite depositional environments which meet the above conditions include;
EVAPORITIC FORMATIONS Evaporite formations need not be composed entirely of halite salt. In fact, most evaporite formations do not contain more than a few percent of evaporite minerals, the remainder being composed of the more typical detrital clastic rocks and carbonates. In order for a formation to be recognised as evaporitic it may simply require recognition of halite Pseudomorphs , sequences composed of some proportion of evaporite minerals, and recognition of mud crack textures or other Textures . ECONOMIC IMPORTANCE OF EVAPORITES Evaporites are important economically because of their mineralogy, their physical properties in-situ and their behaviour within the subsurface. Evaporite minerals, especially nitrate minerals, are economically important in Peru and Chile. Nitrate minerals are often mined for use in the production on Fertilizer and Explosive s. Thick halite deposits are expected to become an important location for the disposal of Nuclear Waste because of their geologic stability, predictable engineering and physical behaviour and imperviousness to groundwater. Halite formations are famous for their ability to form Diapirs which produce ideal locations for trapping Petroleum deposits. MAJOR GROUPS OF EVAPORITE MINERALS
Evaporite minerals start to Precipitate when their concentration in water reaches such a level that they can no longer exist as Solute s. The minerals precipitate out of solution in the reverse order of their solubilities, such that the order of precipitation is: # Calcite (CaCO3) and Dolomite (CaMg(CO3)2) #Gypsum (CaSO4-2H2O) and anhydrite (CaSO4). #Halite (i.e. common salt, NaCl) # Potassium and Magnesium salts Evaporites can also be easily Recrystallized in laboratories in order to postulate the specific characteristics of their formation. SEE ALSO |
|
|