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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

The chemical formula of mineral Rhodochrosite is indicated by MnCO3. Rhodochrosite is a Carbonate mineral. It is known to crystallize in the hexagonal or trigonal system. In optical mineralogy, the 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. Rhodochrosite is a uniaxial negative mineral. Its indices of refraction usually range from 1.597 to 1.816. When viewed closely with the aid of the petrographic polarizing microscope, mineral Rhodochrosite is commonly found having 0.219. This carbonate mineral is commonly found with moderate to high positive relief when viewed under polarized light microscope. This observation may change with stage rotation of the polarized microscope.


            Mineral Rhodochrosite shows a complete solid solution series with siderite. It may contain substantial amounts of zinc, manganese, cobalt, and calcium. Kutnohorite, a member of the dolomite group, is a known intermediate mineral between calcite and Rhodochrosite. The hardness measure of the mineral Rhodochrosite when it is evaluated using the Mohs scale method id usually ranging from 3.5 to 4. The specific gravity measure of the mineral Rhodochrosite is usually 3.70 grams per cubic centimeters. This value usually decreases with calcium and magnesium content and increases with iron and zinc content.


            Rhodochrosite is commonly found in shades of pink in hand sample. It may also appear yellow, gray, or brown. When rubbed on a white porcelain streak plate, it is commonly found leaving a white streak. When viewed in reflected light of petrographic polarizing microscopes, Rhodochrosite is commonly found exhibiting a vitreous luster. Rhodochrosite does not readily react in cold dilute HCl. But then it reacts with effervescence when powdered or if the acid is hot. Rhodochrosite is commonly found colorless to pale pink in thin section or grain mount. Sometimes it may be found with color zoning. Colored varieties of this carbonate mineral may show pleochroism in shades of pink when viewed under polarizing microscopes used in optical mineralogy. The color will appear darkest if the long axis of the rhomb-shaped faces is parallel to the lower polar vibration direction.


            The rare crystals of Rhodochrosite are usually rhombohedral or scalenohedral and often rounded. It usually forms coarse to fine-grained aggregates or grains encrusting other minerals. Rhodochrosite is commonly found having perfect rhombohedral cleavage in one direction like other rhombohedral carbonates. This mineral has lamellar twinning on direction like that of calcite, but is quite uncommon. The extinction of this mineral is usually inclined or symmetrical to cleavage traces and can be found clearly visible under petrographic polarizing microscope. The fast ray vibration direction is parallel to the short diagonal of rhombohedral faces.


            The indices of refraction of mineral Rhodochrosite vary in an approximately linear function of composition. The index of the Rhodochrosite fragments that lie on cleavage surfaces may be found to be about 1.702. The value will increase with the increasing amount of iron, cobalt, or zinc and will typically decrease with calcium and magnesium. Rhodochrosite has extreme birefringence and usually produces creamy high-order colors in thin section and grain mount. This remains true even if the optic axis is nearly vertical. In zoned crystals, the darker-colored areas usually display higher indices of refraction.


            The basal sections of Rhodochrosite usually yield a uniaxial negative figure with numerous isochromes, and isogyres that fan out strongly toward the edge of the field of view of the polarizing microscopes used in evaluation. The fragments of the mineral lying on cleavage surfaces yield strongly off-center figures. Mineral Rhodochrosite may be altered to various dark-colored Mn oxides and hydroxides or may be replaced by other minerals like quartz in order to form pseudomorphs.


            Mineral Rhodochrosite usually displays distinguishing features for it to be identified from the rest of the carbonate minerals. Among its distinguishing features include its indices of refraction, its pink color, and its association with other manganese-bearing minerals, and of course its alteration. This Rhodochrosite mineral is commonly found occurring as a gangue mineral in hydrothermal vein and replacement deposits associated with sulfide minerals, other carbonates, quartz, fluorite, barite, and other manganese-bearing minerals. It may be also found in metamorphosed equivalent of Mn-bearing sediments and in high-temperature metasomatic deposits.

Wednesday, May 28th, 2008 at 5:00 am
The Carbonates and Borates Mineral Class
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