Dolomites calcium-rich

Dolomite is one of the most abundant sedimentary carbonate minerals but its mode of formation and its surface properties are less well known than for most other carbonate minerals. As we have mentioned, the nucleation of dolomites and its structural ordering is extremely hindered. There is a general trend for the "ideality" of dolomite to increase with the age of dolomite over geological time (Morse and Mackenzie, 1990). Most dolomites that are currently forming in surfacial sediments and that have been synthesized in the laboratory are calcium-rich and far from perfectly ordered. Such dolomites are commonly referred to as "protodolomites . Morse and Mackenzie (1990) have reviewed extensively the geochemistry (including the surface chemistry of dolomites and Mg-calcites. 

Zoisite occurs in crystalline schists which are products of regional metamoiphism of basic igneous rocks rich in plagioclase, the calcium-rich feldspar also in argillaceous calcareous sandstones, thulite from quartz veins, pegmatites, and metanioqfiiosed impure limestones and dolomites. 

Figure 7.12. Saturation relations in mixtures of seawater and meteoric water for different solubilities of dolomite. A. Ideal dolomite B. Calcium-rich dolomite. (After Hardie, 1987.)...

In making thermodynamic calculations to determine departure from equilibrium, thermodynamic data for pure stoichiometric calcite and dolomite were used. However, mineralogic and x-ray examination of aquifer material has shown that the calcite may have several mole percent magnesium the dolomite that occurs in the system is generally calcium-rich (13). Therefore, both of these minerals in the natural state have a higher free energy and hence a somewhat higher solubility than the pure minerals. Thus, part of the supersaturation that we have calculated may be more apparent than real. 

Acid soils may be poor in Mg due to parent material and loss by seepage. This is true also for forest soils under the impact of acid rain. In all these cases, fertilizing with Mg-containing compounds is necessary. Examples are dolomite (calcium magnesium carbonate), Mg-rich marls, Mg-rich potassium- and Mg-sulfate fertilizers. Hazardous enrichment of emitted Mg-carbonate is found near older magnesite factories. 

Aj, the determination of which is necessary in only a few mixes, is said to be largely comprised of feldspar, coarse clay or shale particles, dolomite, iron-rich materials, and slag of calcium alumino-silicate composition, each of which, according to Theisen (letter, 1996), has somewhat different effects on the... 

Eftitz R, Kierzkowska AM, Broda M, MUller CR (2012) Highly efficient CO2 sorbents development of synthetic, calcium-rich dolomites. Environ Sd Technol 46 559-565... 

Limestone is homogeneous in chemical composition, mainly containing calcium carbonate, with varying amounts of magnesium (dolomites) and clay (Marschner, 1995 Lugo et al., 2001). On limestone bedrock a variety of calcium-rich soils develop, particularly the rendzinas. Climatic differences determine variations in ion accumulations in the upper soil layers. In drier climates, rapid evaporation causes water-soluble salts to accumulate at the surface. In more hmnid regions, rainfall leaches out both nutrients and calcium carbonate leading to a secondary acidification . 

Subalpine larch commonly grows on previously unvegetated talus slopes covered with granite or quartzite rock, but the species is absent or scarce on limestone and dolomite (Amo and Habeck, 1972). It can also root in bedrock cracks. This substrate preference is in constrast to several other cold-climate conifers, including L. sibirica and tamarack, which often grow on calcium-rich, basic soils (Ritchie, 1957 Hustich, 1966). 

To appreciate the pressure that acid rain has put on sensitive lakes and streams, compare the acidity of rain with the acidity of lake water. Healthy lakes normally have a pH around 5.6 and above. When a lake becomes as acidic as pH 5.0, adverse biological effects set in. At pH 4.5 or below, a lake is usually considered "dead" — incapable of supporting the rich variety of life found in healthy lakes. Yet precipitation in the eastern U.S. is several times more acidic still (average pH 4.3), and in the northeastern U.S. it is as acidic as pH 4.0. Thus if lakes and streams were simply huge puddles of rainwater, every lake east of the Mississippi River would be virtually devoid of life. What prevents this catastrophe is that acid rain is largely neutralized by the soils and rocks underlying most watersheds. The most common alkaline rocks are limestone and dolomite (calcium and magnesium carbonates), which are chemically similar to com-merical stomach antacids. 

To convert calciiun carbonate to dolomite, some of the calcium must have been replaced by magnesiiun, requiring the partial dissolution of the carbonate. This process is promoted by contact with acidic pore water, such as occurs in organic-rich sediments because remineralization produces carbon dioxide. This is probably why dolomites are presently forming in detrital algal mats buried beneath sabkhat. The restricted extent of these modern dolomites reflects a kinetic hindrance to precipitation. Apparently dolomite precipitation in this setting is too slow to form substantial deposits when sea level is rapidly fluctuating. 

In most commercial processes, the compound is either derived from the sea water or from the natural brines, both of which are rich sources of magnesium chloride. In the sea water process, the water is treated with lime or calcined dolomite (dolime), CaO MgO or caustic soda to precipitate magnesium hydroxide. The latter is then neutralized with hydrochloric acid. Excess calcium is separated by treatment with sulfuric acid to yield insoluble calcium sulfate. When produced from underground brine, brine is first filtered to remove insoluble materials. The filtrate is then partially evaporated by solar radiation to enhance the concentration of MgCb. Sodium chloride and other salts in the brine concentrate are removed by fractional crystallization. 

The mineralogical composition of Sahara dust particles shows the predominance of aluminosilicates (clays). Illite is also present in many cases while quartz particles are rare. Scanning Electron Microscopy (SEM) results on dust composition transported over different regions in the Mediterranean Basin have shown that Al-rich clay minerals such as illite and kaolinite are very common in PM10 for Cypms and dominant for Crete. Dust particles are also very rich in calcium which is distributed between calcite, dolomite and sulphates and Ca-Si particles (e.g. smectites) whereas iron oxides are often detected [43]. 

Rasa coal is exceptional because of its high sulfur content, most of which appears to be organic sulfur. The high organic sulfur content is characteristic of marine-influenced bituminous coals. Rasa coal appears to have been formed in a high-pH marine environment where bacteria thrived. This hypothesis is supported by the presence of substantial amounts of both calcite and dolomite in Rasa coal. The calcium- and magnesium-rich environment where Rasa coal formed is expected to have been alkaline. The... 

Thus, water containing HC03 indicates C02-indueed interactions with rocks, and the balancing cations indicate the types of rocks passed calcium comes from interaction with limestone, and calcium and magnesium together come from interaction with dolomite potassium and, even more often, sodium in bicarbonate water come from silicate rocks rich in potassium or sodium feld-spars. 

Bicarbonate-dominated water with TDI concentrations up to about 600 mg/1 has not passed evaporites, and the nature of the rocks interacted with can be deduced from the cations calcium-dominated HC03 water has passed limestone calcium- and magnesium-dominated HC03 water is produced by contact with dolomite sodium-dominated and potassium-rich HC03 waters have interacted with feldspar, plagioclase, and pyroxene contained in igneous or volcanic rocks. 

It has been found that compounds of the alkaline earth metals as well as rare earths are suitable for vanadium trapping. Patents relating to the use of titanates of calcium (22), barium (23), and strontium (24) have been issued. Equivalent stannates of calcium and strontium have also been recommended (24,25). Rare earths as separate particles (26) and in the same catalyst particle (27) have been proposed. Naturally occurring minerals such as Sepiolite and Dolomite which are rich in magnesium oxide and calcium oxide have been suggested (28). 

Dolomites found in nature seldom have exact stoichiometric composition and are frequently structurally rich in calcium (protodolomite). Dolomite, as well as calcite, has a tendency to form solid solutions with many metal ions. Calcite has a tendency to accommodate Mg in its structure to form magnesian calcite. Kineticall>, the deposition of magnesian calcite may be more favorable than the deposition of dolomite. 

The coating of the bed particles exhibited several thin layers. The majority of the particles were fust coated with calcium and phosphorus with the outermost layer being magnesium-rich. It is probable that the formation of these layers protects d particles from agglomeration. Further evidence for this conclusion is found from a test where dolomite was added to silica sand bed to prevent agglomeration. A similar layered coating was found in the silica sand bed particles. 

Most of the dolomites (including the detrital cores) have calcium-enriched compositions (Table 6 Fig. 8). Zoning within the ferroan dolomite is clearly visible in back-scattered electron images, and the higher Fe contents tend to be characteristic of the later zones (Fig. 7A). The degree of Ca enrichment, however, is not strongly controlled by Fe content and more Fe-rich portions of the crystals display a range in Ca content that is nearly as broad as that of less Fe-rich portions. Mn content is correlated positively with Fe enrichment (Fig. 9). 

Trace element substitution in the early marine dolomite from the central basin is relatively Fe rich, with slight excess calcium substitution from the ideal formula Ca/(Mg -i- Fe -h Mn) = 1, and very little Mn substitution (Boles Ramseyer, 1987). Excess Ca is about l-4mol%. Typical compositions have... 

The intergranular carbonate cement is always iron-rich dolomite (or ankerite). Electron probe microanalysis gives between 7 and 18 mol% FeCOj (and 0.2-0.8 mol% MnCOj) (Fig. 11). The calcium content of the dolomites is relatively stoichiometric, with an average of 51 mol% CaCOj (range 50.0-53.3 mol%). The cement is generally dull to very dull red-brown in CL, with subtle concentric zonation. It is relatively homogeneous when examined in BSEM, suggesting that intracrystalline chemistry is reasonably consistent within and between individual fractures. The dolomite crystals have a variable fluid inclusion density, with a vast preponderance of monophase aqueous inclusions. Any two-phase inclusions identified in thin section... 

Carbon is the twelfth most abundant element in the Earths crust, although it accounts for only c.0.08% of the combined lithosphere (see Box 1.2), hydrosphere and atmosphere. Carbon-rich deposits are of great importance to humans, and comprise diamond and graphite (the native forms of carbon), calcium and magnesium carbonates (calcite, limestone, dolomite, marble and chalk) and fossil fuels (gas, oil and coal). Most of these deposits are formed in sedimentary environments, although the native forms of C require high temperature and pressure, associated with deep burial and metamorphism. 

Dolomlto Tablets or powdered, made Irom ground dolomitic limestone. Nutritional supplement that provides calcium, magnesium, and other minerals. Rich source ol calcium, magnesium, and other minerals. May also he used as an antacid The consumption ol excessive amounis may reduce the absorption ol certain trace minerals. 

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