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The chemical formula of Dolomite is indicated by CaMg(CO3)2 or Calcium Magnesium Carbonate. Dolomite is a Carbonate mineral. It is known to crystallize in the hexagonal system. In optical mineralogy, hexagonal system of crystallization comprises crystals having four axes. Three of which are positioned in a single plane with equal length and are symmetrically spaced. The fourth axis is found to be perpendicular to the other three axes. Dolomite has uniaxial negative figure. It is commonly found having low negative to high positive relief and this change as the stage of petrographic polarizing light microscope is rotated. It is commonly used in some cements and it is also considered as a source of magnesium. Dolomite is also used as a mineral specimen and it usually exhibits fascinating microscope images under polarizing light microscopes. Dolomite was named after Deodat Guy Tancrede Gratet de Dolomieu (1750 to 1801), a French mineralogist and geologist. The mineral was first discovered in the year 1791.

 

            Dolomite forms tetrahedrons and this is actually its typical crystal habit. Dolomite crystals also tend to curve into a saddle-shaped crystal. This is maybe brought about by the twinning effects on the crystal. The Dolomite specimen that possesses this unique habit is considered as classical dolomite. This is because not all Dolomite specimens are curved. Some appear as impressive specimens exhibiting a well-formed crystal with sharp rhombohedrons. Dolomite also exhibits a unique and maybe the best illustration for pearly luster in reflected light of polarized microscopes. This pear-like effect is actually best illustrated on the curved crystals as light sweep across the curved surface of the crystal. Mineral Dolomite can be actually found in variety of colors but the most common among them all are the colorless and white crystals. A pink Dolomite crystal on the other hand is considered as another unique characteristic of dolomite. Attractive Dolomite specimens are usually exhibiting typical pink color, unusual crystal habit and pearly luster in reflected light of polarizing microscopes for geologists.

 

            Dolomite is usually white, colorless, gray, yellowish brown to brown in hand sample if iron content increases. It is less commonly found pink or pinkish. When evaluated under petrographic polarizing light microscopes it can be also found black when iron is present in the crystal. It usually exhibits a vitreous to pearly luster in reflected light of geological polarizing microscope. Dolomite vigorously effervesces in dilute HCl only if powdered or if acid is hot. High iron content has magnetic effect after heating. Dolomite usually appears colorless in thin section or grain mount. Although weathered or altered, iron-rich samples may be brownish due to the presence of iron oxides and hydroxides. Dolomite is usually found having perfect rhombohedral cleavage that can be seen more clearly visible when viewed with the aid of the petrographic polarizing light microscope. The fracture found is commonly conchoidal when the mineral is viewed in plane light of geological polarizing microscopes. The hardness measure of the mineral using the Mohs scale method is usually ranging from 3.5 to 4. When the mineral is rubbed on a white porcelain streak plate, it is commonly found leaving a white streak. The specific gravity measure of the mineral Dolomite is commonly found as 2.86 grams per cubic centimeters, which is considered average.

 

            Most Dolomite crystals are found transparent to translucent in appearance. The crystal habit of the mineral usually include saddle-shaped rhombohedral twins and simple rhombs while some other have slightly curved faces that can be very interesting when viewed under polarized microscopes. Some Dolomite crystals are prismatic, massive and granular. Others are rock-forming usually exhibiting nice microscope images under geological polarizing microscopes. Dolomite never exhibits scalenohedrons. Lamellar twinning is moderately common and this usually produces lamellae that may be parallel either to the long or the short diagonal of the rhombohedral faces. Simple twins may also be found.

 

            The extinction is usually found symmetrical or inclined to cleavage traces. The fast ray usually vibrates parallel to the long diagonal of cleavage rhombs. The refractive index of the mineral is usually found ranging from 1.679 to 1.500 when it is viewed with the aid of polarized light microscopes. The maximum birefringence found displayed by the mineral in plane-polarized light of polarizing microscopes is usually ranging from 0.179 to 0.181. Dolomite may fluoresce in either short wave or long wave ultra violet light. Mineral Dolomite is also found anomalously biaxial. Dolomite mineral, unlike calcite, effervesces weakly with warm acid or when first powdered with cold hydrochloric acid. Dolomite is commonly associated with other interesting minerals like calcite, quartz, sulfide ore minerals, fluorite, barite and occasionally with gold. Mineral Dolomite is not radioactive species. There is no specific data found on the toxicity and health dangers for mineral Dolomite. However, specimens of this mineral species should be treated with great care and use of sensible precautions is advised upon handling them.

 

            Mineral Dolomite is a common sedimentary rock-forming mineral that exhibits interesting microscope images under polarizing light microscopes. Dolomite is only one of the few sedimentary rocks that still undergo very significant transformations after they are deposited. They are once calcite or aragonite rich limestone that altered to dolomite after the process called diagenesis.  The process is not even close to metamorphism but a very much shorter than that. Mineralogists wondered why there are so many shales, limestones and sandstones formed but no dolomite. Until now reasons are still locked. Dolomite can be best found probably in tropical areas near ocean environments while those magnesium rich ground waters, which contains significant amount of saline waters are somewhat crucial and warm form the formation of Dolomite. Dolomite minerals are commonly found in massive beds that are several hundred feet thick. This mineral is quite common and can be found all over the world. They are most especially found common in sedimentary rock sequences. Dolomite mineral can be also found in metamorphic marbles, hydrothermal veins and replacement deposits. The best field indicators of mineral Dolomite usually include luster, typical pink color, and density, slow reaction to acid, crystal habit and hardness. Dolomite notably occurs at some famous mineral localities including Mexico, Switzerland, Ontario in Canada, in Midwestern quarries of the United States, Pamplona in Spain and many other localities around the world.



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Monday, April 28th, 2008 at 3:33 am
Category:
The Carbonates and Borates Mineral Class
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