Kutnohorite and dolomite are iso-structural. Dolomite mineral shows variation not only in chemical composition but also in the atomic arrangements.
Very few, if any, sedimentary dolomites are truly stoichiometric [CaMg CO3 2]. In practice, dolomite mineral is better represented as Ca 1-x Mg 1-y CO3 2. Documented compositions range from Ca 1. Thus, the term dolomite describes a mineral series that encompasses a range of chemical variation and lattice structures.
It encapsulates an array of natural Ca-Mg carbonates with chemical compositions close to ideal dolomite, but with weak or diffuse X-ray reflections that indicate varying degrees of cation disorder. There are several varieties of dolomite mineral, each with different thermochemical properties depending on the degree of lattice ordering and non-stoichiometry. Structure of dolomite crystal and bonding of water molecules with the crystal of dolomite are shown in Fig 1.
Fig 1 Structure of dolomite crystal and bonding of water molecules with the crystal of dolomite. When dolomite is heated, the carbonates present in the dolomite are decomposed and CO2 is released. The calcined dolomite has a composition of CaO. The calcination reaction takes place in two steps.
The decomposition temperature is dependent on the partial pressure of the CO2 present in the process atmosphere.
Since during calcination, CO2 is removed from the raw dolomite, the calcined dolomite i is porous ii has higher surface area, iii has high reactivity, and iv is hygroscopic. The calcined dolomite is alkaline in nature. Dolomite has several uses. Since very early days, it is being used as ornament stone. For some uses, dolomite is specifically valued for its MgO content and chemical composition is all important. It is being used in raw form, calcined form or in sintered form.
It is being used as construction material, in agriculture and in industry. In industry it is being used i as a fluxing material, ii as a refractory material, and iii as a filler material. The major industries where dolomite is being used are iron and steel industry, ferro alloy industry, plastic industry, ceramic industry, glass industry, fertilizer industry, and soap and detergent industry etc. As construction material, dolomite is crushed and sized for use as a road base material, an aggregate in concrete and asphalt, railroad ballast, rip-rap armour shorelines, streambeds, bridge abutments, pilings and other shoreline structures against scour and water erosion , or fill.
Dolomite is chosen as a construction material due to its increased hardness and density. Asphalt and concrete applications prefer dolomite as filler because of its higher strength and hardness.
In iron and steel industry, the main uses of dolomite are i as a fluxing material ii for protection of refractory lining, and iii as a refractory raw material. Dolomite in iron and steel industry is normally used in three forms.
These are i raw dolomite which is also the natural form of dolomite, ii calcined dolomite, and iii sintered dolomite. When dolomite is used as a fluxing material then it is used as either raw dolomite or calcined dolomite. When dolomite is used for the protection of refractories, it is used in calcined form and when dolomite is being used as a refractory raw material, it is used in the form of sintered dolomite.
In the chemical industry, dolomite is used as a source of MgO. In agriculture, dolomite is used as a soil conditioner and as a feed additive for livestock. Dolomite has been used as a minor source of magnesium, but today most magnesium is produced from other sources.
Calcined dolomite is also used as a catalyst for destruction of tar in the gasification of biomass at high temperature. Dolomite is relatively soft and can easily be crushed to soft powder. Dolomite powder is used in agriculture to reduce soil acidity and also to adjust magnesium deficiency. Magnesium is an important plant nutrient. Dolomite powder is used as filler in various products like detergent, paints, rubbers, agriculture products, animal feed, putty, and other adhesives and sealants,.
It is used in the manufacture of plastics as well as ceramic tiles. Dolomite is finely ground to precise size specifications. An alternative name sometimes used for the dolomitic rock type is dolostone. Dolomite is an unusual carbonate mineral. It is common in ancient platform carbonates, yet it is rare in Holocene sediments Table 1.
On the basis of the mode of formation, dolomites can broadly be divided into two groups: primary dolomite and secondary dolomite. The widely accepted hypothesis of dolomitization is that limestone is transformed into dolomite by the dissolution of calcite followed by dolomite precipitation.
Dolomite is formed by the replacement of the calcite ions by the magnesium ions. Depending upon the ratio of the Mg ions in the crystal lattice they have different names Figure 1.
Modern dolomite formation has been found to occur under anaerobic conditions in supersaturated saline lagoons in Brazil. Primary dolomite is indeed infrequent and often forms in lakes and lagoons while most of dolomite is from the replacement origin.
Dolomite is in fact formed in high intertidal supratidal and sabkhas environment. Dolomitic that formed in the supratidal environment are precipitated from evaporated sea water. This process comprises the formation of dolomitizing solutions over vaporization of lagoon water or tidal flat pore water besides then the succession of these solutions into nearby carbonate rocks Figure 3. This type of dolomite formed by the mixing of seawater with the fresh water. The source of water may be rainwater Figure 4.
Burial dolomitization involves prime mechanism which is the dewatering of basinal mud rocks due to compaction and removal of Mg-rich fluids into neighboring shelf edge. Expulsion of water and changes of clay minerals with enlarged burial and increasing temperature suggest that it would liberate Mg ions along with Fe ion. The diagenesis of basinal shales are generally organic-rich and the diagenesis would contribute to CO 3 ions.
Seawater itself can also be a source of dolomite because it contains the sufficient amount of Mg ions with little modification if a good pumping process exists. Dedolimitization refers to the partial to the whole transformation of former dolomite rocks to a calcian rich rock. The dolomitization can be considered as a kind of process in which Mg is gradually released. The dedolomitization process can be divided into two steps,. Dolomitization is a geological process by which the carbonate mineral dolomite is formed when magnesium ions replace calcium ions in another carbonate mineral, calcite.
It is common for this mineral alteration into dolomite to take place due to evaporation of water in the sabkhas area. Dolomitization involves a substantial amount of recrystallization.
This process is described by the stoichiometric equation. The conditions of dolomite formation are difficult to govern in the laboratory as up to yet no-one has been capable to form it at low temperatures from usual H2O. For undeviating result of dolomite formation the equation is:. Sea water is thought to be the prime source of magnesium ion for early diagenetic surface and near-surface dolomitization. It consists part per million magnesium 0.
Dolomite is one of the complex mineral and its artificial occurrence is difficult to study in lab experimentations. Though it is a very well-ordered mineral and demanding phase to precipitate, yet still dolomite synthesis at sedimentary tempratures using natural waters has not shown.
Controlling chemical factors on dolomite formation from water is problematic to clarify and largely have been concluded from high-temperature experimentations 9 Figure 5. Figure 5 Essential elements of any dolomitization model, supply of Mg and the supply of carbonate must be sufficient to form the observed amount of dolomite there must be a delivery mechanism commonly in the form of fluid flow adequate to deliver these ions to the dolomitization site and lastly there must exist favorable condition for chemical reaction.
For elucidation of primeval dolomite five extensive divisions of dolomitization model presently exists,. Figure 7 Conceptual models for a dolomite precipitation and b dolomite replacement scenarios. The dashed lines represent the dolomite precipitation rates t 1 and t 2 represent two different time slices. Dolomite precipitation front is moving towards the right as indicated by the open arrow. Again t 1 and t 2 represents two different time slices. Figure 6 Models of dolomitization, illustrating the variety of mechanisms for moving dolomitizing fluids through the sediments.
Formation of dolomite by replacement of CaCo 3 ranges from fabric damaging to retaining and from fabric selective to persistent. The important aspects now are grain mineralogy and crystal extent, the timing of dolomitization and natural surroundings of dolomitizing liquids.
Forms of dolomite crystals in replacement assortments differs from anhedral to euhedral shape, with the terminologies xenotopic and idiotopic denoting to the mosaics. Sibley 11 put stress on the origin of crystal boundary shapes, identifying non-planar, euhedral and subhedral categories Figure 8 Figure 9.
Figure 8 Three common dolomite textures; A Non-planar crystals in a xenotopic mosaic; B Planar-e crystals e for euhedral in an idiotopic mosaic; C Planar-s crystals s for subhedral in a hypidiotopic mosaic Sibley et al.
These two minerals are one of the most common pairs to present a mineral identification challenge in the field or classroom. The best way to tell these minerals apart is to consider their hardness and acid reaction. Calcite is also strongly reactive with cold hydrochloric acid, while dolomite will effervesce weakly with cold hydrochloric acid.
Dolomite aggregate: Dolostone, used for asphalt paving from Penfield, New York. Dolomite occurs in a solid solution series with ankerite CaFe CO 3 2. When small amounts of iron are present, the dolomite has a yellowish to brownish color. Dolomite and ankerite are isostructural. Kutnahorite CaMn CO 3 2 also occurs in solid solution with dolomite. When small amounts of manganese are present, the dolomite will be colored in shades of pink. Kutnahorite and dolomite are isostructural.
Dolomitic marble from Thornwood, New York. The best way to learn about minerals is to study with a collection of small specimens that you can handle, examine, and observe their properties. Inexpensive mineral collections are available in the Geology. Dolomite as a mineral has very few uses.
However, dolostone has an enormous number of uses because it occurs in deposits that are large enough to mine. The most common use for dolostone is in the construction industry. It is crushed and sized for use as a road base material, an aggregate in concrete and asphalt, railroad ballast, rip-rap, or fill.
It is also calcined in the production of cement and cut into blocks of specific size known as "dimension stone. Dolomite's reaction with acid also makes it useful. It is used for acid neutralization in the chemical industry, in stream restoration projects, and as a soil conditioner. Dolomite is used as a source of magnesia MgO , a feed additive for livestock, a sintering agent and flux in metal processing, and as an ingredient in the production of glass, bricks, and ceramics.
Dolomite serves as the host rock for many lead , zinc , and copper deposits. These deposits form when hot, acidic hydrothermal solutions move upward from depth through a fracture system that encounters a dolomitic rock unit. These solutions react with the dolomite, which causes a drop in pH that triggers the precipitation of metals from solution.
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