Dolomite properties

Thermal Properties. Because all limestone is converted to an oxide before fusion or melting occurs, the only melting point appHcable is that of quicklime. These values are 2570°C for CaO and 2800°C for MgO. Boiling point values for CaO are 2850°C and for MgO 3600°C. The mean specific heats for limestones and limes gradually ascend as temperatures increase from 0 to 1000°C. The ranges are as follows high calcium limestone, 0.19—0.26 dolomitic quicklime, 0.19—0.294 dolomitic limestone, 0.206—0.264 magnesium oxide, 0.199—0.303 and calcium oxide, 0.175—0.286. 

Talc of metasedimentary origin is formed by hydrothermal alteration of a dolomitic host rock by a silica-containing fluid. This type of deposit is typical of Montana and AustraUa. It is usually quite pure with talc content of 90 to 98% and often very white as well. Dolomite [17069-72-6], CaMg(C02)2, is the most common accessory mineral. The fourth type is of metamorphic origin, where a siUcaceous dolostone is first converted to tremolite [14567-73-8] or actinohte [13768-00-8] and then partially converted to talc. The Balmat, New York, and Death Valley, California, deposits are of this type. Tremolite, dolomite, and serpentine are common accessory minerals. This type of talc deposit has a variable talc content (30—80%), but is usually white and often commercially exploited because of the properties of its accessory minerals rather than the talc. 

Magnesium. Mg, at wt 24.312, at no 12, valence 2. Isotopes 24 (77.4%), 25 (11.5%) 26 (11.1%). Physical properties of 99.9% pure Mg are (riven in the fnllnwino tsKle fRef 10 n 6791 Mg is very abundant in nature, occurring in substantial amounts in many rock-forming minerals such as dolomite, magnesite, olivine, and serpentine. In addition, it is also found in sea water, subterranean brines, and salt beds. 

In arid and semi-arid soils, calcite, dolomite, leonhardite (Ca2Al4Si8024.7H20) and lawsonite (CaAl2Si208.2H20) can be possible minerals. Calcium carbonate strongly influences soil properties in arid and semi-arid soils. Most calcareous soils have soil a pH in the range of 7.3-8 5. When sodium is predominant in soils, soil pH is above 8.5. In most arid and semi-arid soils, calcium carbonates (calcite and dolomite) generally accumulate and are most likely to control the Ca2+ and Mg2+ solubility in these soils (Lindsay, 1979). 

In fact, the choice of CO2 fugacity has little effect on the mineralogical results of the mixing calculation. In the model, the critical property of the Fountain fluid is that it is undersaturated with respect to calcite, so that calcite dissolves when the fluid mixes into the Lyons. Because we assume equilibrium with dolomite and magnesite, the saturation index (log Q/K) of calcite is fixed by the reaction... 

The treatment process and flotation properties of pyrochlore are very much dependent on the gangue composition of the ore. The selective flotation of pyrochlore from carbonatite ore is not possible since calcite and dolomite have similar flotation properties as pyrochlore. In addition, in the presence of carbonates, the stable pH required for flotation of pyrochlore (i.e. 5.0-5.5) cannot be maintained. 

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. 

Another aspect of minerals and rocks laser-induced luminescence became important recently, especially in Israel. Terrorists have intensively used roadside Ijombs, while the plastic covers simulating local rocks have been used for camouflage of explosive materials. The possibilities of the luminescence method have been checked for the remote detection and identification of such camouflage materials. The luminescence properties of the colored plastics have been investigated in comparison with the corresponding properties of the dolomite rocks, which are imitated. 

The steady-state luminescence spectra of three different plastics are characterized by blue luminescence with Amax = 445-465 nm, while much broader liuninescence band with yellow color characterizes the dolomite rocks. These spectra are different, but not enough to differentiate between them from big distance. The decay properties have been also checked in order to improve the selective feature. It was found that luminescence intensity of rocks in the blue part of the spectrum is drastically diminished after specific delay time, while the decrease of intensity in the yellow part of the spectrum is mush more moderate. Liuninescence intensity of all plastics also diminishes after such delay, nevertheless remaining mush stronger then intensity of rocks luminescence in the blue part of the spectrum. The comparison of plastic and rock time-resolved spectra in specific time window clearly demonstrate that they are absolutely different, which made confident discrimination possible (Fig. 7.3). 

Dolomite is an alternative mineral that is used in some regions in place of cal-cite for certain applications. Dolomite is a calcium magnesium carbonate (CaCOj.MgCOj) and occurs widely in nature. Although generally similar to cal-cite in properties, it is shghtly harder (3.5), denser (2.85) and more acid resistant. Production is similar to that for calcite,but miUing is more costly and it tends to only be available at the coarser end of the size spectrum. 

Dolomite Dolomite is one of the most abundant sedimentary carbonate minerals, yet after years of intense study its mode of formation remains controversial, and its properties under Earth surface conditions are less well known than for most other carbonate minerals. The primary reason for this seems to be that its formation is kinetically hindered by its complex and well-ordered structure. Another problem in understanding dolomite may be as Lynton Land says "there are dolomites and dolomites and dolomites". The topic of dolomite genesis will be dealt with in several later sections of this book. 

Figure 8.25. Some chemical and diagenetic properties of organic-rich marine sediments as a function of depth based on DSDP interstitial water profiles. A. Schematic gradients of SO42-, total alkalinity, Ca2+ and Mg2+ in pore waters, and zones of sulfate reduction, methanogenesis and fermentation. Magnesium diffuses into the sediment and organogenic dolomite forms at depth. B. Logarithm of calculated saturation states of interstitial waters with respect to dolomite. Dolomite saturation=0. All these pore waters are oversaturated with respect to dolomite. (After Compton, 1988.)...

Calcium carbonate is the most commonly used extender. It is widely available and low in cost, and it provides for improvements in certain performance properties. The material is a mineral that is mined throughout the world. Common forms of calcium carbonate include limestone, marble, calcite, chalk, and dolomite. It is manufactured by precipitation processes and is commercially available from a number of sources. Calcium carbonate is available in many different particle sizes and in various grades. To improve dispersion in certain resins, the filler is often coated with calcium stearate or stearic acid. 

Using fixed dolomite guard beds to lower the input tar concentration can extend Ni catalyst lifetimes. Adding various promoters and support modifiers has been demonstrated to improve catalyst lifetime by reducing catalyst deactivation by coke formation, sulfur and chlorine poisoning, and sintering. Several novel, Ni-based catalyst formulations have been developed that show excellent tar reforming activity, improved mechanical properties for fluidized-bed applications, and enhanced lifetimes. 

Composite cements may contain mineral additions other than, or as well as, ones with pozzolanic or latent hydraulic properties. Regourd (R34) reviewed the use of ground limestone, which is widely used in France in proportions of up to 27%. The limestones used consist substantially of calcite, with smaller proportions of quartz or amorphous silica and sometimes of dolomite. They must be low in clay minerals and organic matter because of the effects these have on water demand and setting, respectively. The XRD peaks of the calcite are somewhat broadened, indicating either small crystallite size or disorder or both IR spectra confirm the occurrence of disorder. 

In such cases, the alkali enters the vapor phase by vaporization from coal minerals, dolomite (10) or limestone, as in sulfurscrubbing processes, or from air-ingested salt particles (e.g., in marine environments). Hardesty and Pohl ( ) have recently reviewed the major problem areas and data limitations relating to the properties of coal mineral matter and ash. 

Calcite and dolomite form large parts of the sedimentary continental crust. Consequently, their mechanical properties have been studied in some detail, and Wenk et al. (1983) have reviewed the rheology and associated microstructural development. Deformation takes place by both twinning and dislocation glide. 

Tribble J. S., Arvidson R. S., Lane M., Ill, and Mackenzie F. T. (1995) Crystal chemistry, and thermodynamic and kinetic properties of calcite, dolomite, apatite, and biogenic silica applications to petrologic problems. Sedim. Geol. 95, 11-37. 

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