Minerals dolomite, CaMg

Magnesium is mined in significant quantities from the minerals dolomite (CaMg(C03)2) and magnesite (MgC03) and in smaller quantities from brucite (Mg(OH)2) and carnallite (KMgCl3 x 6(H20)). 

Dolomite rock is defined as a carbonate rock, containing calcite <50 %, dolomite >50 %. (Visser 1980). The term dolostone has been coined to avoid confusion with the mineral dolomite, CaMg (003)2, but has not gained general acceptance. 

Description and general properties. Dolomite is a massive calcareous sedimentary rock made of the mineral dolomite [CaMg(C03)j, rhombohedral], first identified by the French geologist D. Dolomieu in 1791 and named by H. Saussure after its discoverer. Dolomite occurs as huge geological formations such as in the northeastern Italian Alps called the Dolo-miti. Usually dolomite as a rock contains, apart from dolomite, other carbonates (e.g., calcite. 

This rule can be applied to both electronic and dielectric polarizabilities, but here we discuss the rule only insofar as it applies to dielectric polarizabihties. The molecular or oxide additivity rule has been applied to hydrates, to the compounds MTiOs where M = Mg, Ca, Sr, and Ba, to dolomite (CaMg(C03)2), zircon (ZrSi04), and spinel (MgAl204), to several titanates andzirconates andKMgFs, and to a variety of minerals. " ... 

XRD analysis has revealed the presence of several different types of carbonate minerals in liquefaction residues from a number of coals. Minerals identified included vaterite and calcite (two polymorphs of CaCO,) dolomite (CaMg[C03]2) and in the residue from a high sulfur coal (2.26 db), anhydrite (CaSO,) was identified. The types of mineral deposits formed depend not only on the coal but also on the reaction conditions. Our data indicates that whilst vaterite forms at low temperatures (380°C), as the temperature increases, the vaterite becomes progressively converted to calcite, the more stable form. After further increases in temperature, particularly at long reaction times, dolomite begins to form. 

The most abundant carbonate minerals in mine wastes are calcite [CaCOs], dolomite [CaMg(C03)2], ankerite [Ca(Fe,Mg)(C03)2], siderite [FeC03] or mixtures thereof. The dissolution of calcite can be described as... 

The regional distribution of hardness (i.e. Ca plus Mg) is shown in Fig. 4. This probably reflects the distribution of free carbonates in the sediments with areas of hard water reflecting their presence and low hardness areas reflecting their absence. The most probable carbonate minerals are calcite (CaCOs) and dolomite (CaMg(C03)2). The absence of pH and bicarbonate data from the National Hydrochemical Survey dataset means that saturation indices for these minerals could not be calculated. However, data from the three Special Study Areas (Smedley et al., 2001) suggest that there is both calcite and dolomite saturation, even slight supersaturation. 

Limestone (chiefly calcite, CaCOa) and dolomite rocks (chiefly dolomite, CaMg(C03)2) are exposed at about 20% of Earth s surface. Carbonate detritus, fossil shell materials, and carbonate cements are also common in noncarbonate sedimentary rocks and arid-climate soils. The carbonate minerals found in such occurrences, in decreasing order of importance, are calcite, dolomite, magnesian cal-cites (Cai jMgfCOa where jc is usually <0.2), aragonite (a CaCOa polymorph) and, perhaps, magnesite. As a rule of thumb, when such materials are present in silicate or aluminosilicate rocks or soils at a level of about 1 % or more, they will lend to dominate the chemistry of the soil or ground-water. This fact is extremely important when one is concerned about the ability of a rock to neutralize acid mine waters, other acid wastewaters, or acid rain. 

It has been noted that the chemical composition of minerals could vary within specified limits. This phenomenon is known as sofid solution. For example, the chemical composition of the mineral dolomite is commonly designated as CaMg (C03)2, or as (Ca, Mg)CO. This does not mean that dolomite has calcium and magnesium existing in a one-to-one ratio. It signifies that dolomite is a carbonate mineral that has significant amounts of... 

Magnesium oxide (MgO, magnesia) occurs naturally as the mineral periclase, a metamorphic mineral formed by the breakdown of dolomite, CaMg(C03)2, and other magnesium minerals. Occurrences of periclase are rare and are of no commercial importance. The principal commercial sources of MgO are magnesite (MgCOs) and magnesium hydroxide [Mg(OH)2]. 

Carbonates of alkaline-earth and other divalent metals are crystalline phases of noteworthy importance both in the earth sciences, as rock-forming minerals, and in chemical technology, as raw materials for a number of industrial processes. In particular, the calcite polymorph of CaCOs and dolomite, CaMg(C03)2, are present in huge quantities in the earth s crust as main constituents of limestones (sedimentary rocks), and are also important minerals of several metamorphic rocks. 

The dissolution increases alkalinity (HCOa ) with the added benefit of increasing an equivalent amount ofhardness (Ca ). Limestone is a sedimentary rock primarily composed of calcite, aragonite and vaterite. Calcite can be pure in composition (CaCOa) or can contain low concentrations of magnesium-forming magnesium calcite. Natural limestone can contain minerals or impurities such as dolomite [CaMg(C03)2] and quartz (Si02). 

The most common nonphosphalic accessory minerals associated with sedimentary phosphate rocks are quaife— clays, and two carbonates dolomite (CaMg(C03)2) and calcite (CaCOs). Carbonate-cemented phosphate rocks are particularly noteworthy because of their abundance. McClellan and Gremillion [14[ estimated that there are 3 tonnes of carbonate-cemented phosphate rock for every tonne of ore that could be handled by conventional milling and flotation processes (quartz- and clay-containing phosphate rocks). 

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