Mineral components, accumulation

Smectite is the first secondary mineral to form upon rock weathering in the semi-arid to sub-humid tropics. Smectite clay retains most of the ions, notably Ca2+ and Mg2+, released from weathering primary silicates. Iron, present as Fe2+ in primary minerals, is preserved in the smectite crystal lattice as Fe3+. The smectites become unstable as weathering proceeds and basic cations and silica are removed by leaching. Fe3+-compounds however remain in the soil, lending it a reddish color aluminum is retained in kaolinite and A1-oxides. Leached soil components accumulate at poorly drained, lower terrain positions where they precipitate and form new smectitic clays that remain stable as long as the pH is above neutral. Additional circumstances for the dominance of clays are ... 

The intercept term C Ar/ Ar)o, which accounts for igneous, metamorphic, or atmospheric sources, is regarded as the excess contribution present at time = 0, whereas the second term is the radiogenic component accumulating in the various minerals of the isochron by decay of If all the minerals used to construct the isochron underwent the same geologic history and the same sort of contamination by excess " Ar, the slope of equation 11.100 would have a precise chronological... 

Methane formed millions of years ago from microscopic underwater plants and bacteria that dropped to the bottom of the ocean when they died. Over millions of years, they were crushed and heated by the pressure of layers of sand, dirt, and other materials that accumulated on top of them. The mineral components of the undersea mud gradually turned into a type of rock known as shale. Some of the organic components turned into natural gas, which is mostly methane. The natural gas became trapped in porous rocks called reservoir rocks and in larger pockets of the rock called reservoirs or geologic traps. Natural gas is now found in... 

Sulphates are most competitive acceptors in the reducing environment and they slow down other reduction processes until their concentration drops below 1.0 mmole-T. With exhaustion of free oxygen, nitrate nitrogen, Mn and Fe oxides and sulphates the store of easily available sun energy, accumulated by the pasturable trophic chain, end, and Eh value declines below —0.25 V. Along with this ends the activity of chemo-litho-heterotrophs, which used carbon of the organic matter and electrons for its oxidizing from oxidized mineral components. 

Continental aerosol particles contain a significant fraction of minerals. The insoluble fraction consists mainly of the major crustal elements silicon, aluminum and trivalent iron, which occur as alumino-silicates, quartz, and iron oxides. Elements that are eluted from minerals by water are sodium, potassium, calcium (inpart), and magnesium. The water-soluble inorganic salt ftaction is dominated by am-monimn sulfate. Again, sulfate arises from the oxidation of sulfur dioxide, both by gas-phase and by aqueous phase reactions. Whereas the mineral components are mainly found in the coarse particle size range, ammonium sulfate resides mainly in the accumulation mode. Nitrate occurs partly in association with ammoniirm in the accumulation mode, and partly together with sodiirm and other cations in the coarse particle mode. Thus, nitrate often shows a bimodal size distribution. 

The limitation of these instruments is that they only indicate overall corrosion rate. Their sensitivity is affected by deposition of corrosion products, mineral scales or accumulation of hydrocarbons. Corrosivity of a system can be measured only if the continuous component of the system is an electrolyte. 

Movement of carbonates and salts can also occur in a similar fashion. As these minerals are weathered in the upper soil profile, their component ions go into solution and are moved down through the soil by rainfall entering the soil. As the water moves down the soil there may not be enough water to move the ions out of the soil, so they precipitate in a lower horizon where they accumulate. Such accumulations are common in arid environments with limited rainfall. In high rainfall areas, carbonates and salts are usually completely removed from the soil through leaching. 

Case III, An Excess of One Component Is Necessary.— It sometimes happens that an excess of one component is requisite for the formation of a double salt. Conversely, if the solid double salt is dissolved and the solution is evaporated, one of the components separates until the required excess of the other component has accumulated in the solution. This case is well illustrated by the mineral carnallite, KCl-MgCl2-6H20, one of the products of the Stassfurt mines. Let the point A (Fig. 20), represent a saturated solution of potassium chloride and the points, a saturated solution of magnesium chloride. An unsaturated solution of equivalent quantities of the two salts is then represented on the line OE, say at a. If the solution is evaporated at constant temperature (20°), the point a approaches the solubility curve of potassium chloride, viz., the line AC. At E, potassium chloride begins to separate and continues to do so until the representative point has moved to C, at which point carnallite makes its appearance. Since the separation of carnallite withdraws the two salts in equimolecular ratio from the solution, and since the solution now contains much more magnesium chloride than potassium chloride, the deposits of crystals of carnallite leave the solution unsaturated with respect to potassium chloride, and the latter salt steadily passes into solution again, while the deposit of carnallite increases. If, when the point C is reached, the crystals of potassium chloride are... 

The main components of marine sediments are inorganic aluminosilicate minerals which are usually accumulated on the sea floor by river and other geological activities, and also skeletons and shells of marine organisms (mainly calcium carbonate and silica) [2]. Of course, some metal salts or particulates which precipitate from seawater form new minerals, e.g. manganese nodules [2]. The chemical compositions of the three principal types of sediments in the ocean are shown in Table 12 [105], Most of the sediments found in the deep-sea floor are mixtures of these three principal minerals. Study of the sediments in the oceans and seashores can provide important data related to geochemical, oceanographical or biological circulation and deposition of elements, formation and distribution of marine sediments, and exploitation of marine resources. 

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