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The chemical formula of mineral Bastnasite is indicated by (Ce,La,Y)CO3F, Cerium Lanthanum Yttrium Carbonate Fluoride. Bastnasite is actually a Carbonate mineral. Bastnasite chemical structure is usually made up of stacks of carbonate ion layers and CeF layers. It can be found that the CeF layers actually form flat hexagonal sheets with an obvious bonding of each cerium atom to the three fluorines. The carbonate layers on the other hand are considered more complex with angled carbonate triangular groups. The structural arrangement of the atoms of the mineral is closely evaluated because it is considered as one of the few rare earth mineral structures that can actually accommodate variously sized cations. Bastnasite mineral specimen was first discovered in the Bastnas mining area found in Sweden. It was named after its type of locality the Bastnas Mine, Riddarhyttan, Vastmanland, Sweden.

 

            Bastnasite minerals are known to crystallize in the hexagonal system, which can be clearly found when specimen is viewed with the aid of petrographic polarizing microscope. In the field of 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. Its crystals are usually found translucent to opaque in appearance. Bastnasite crystals can be also found forming uneven flat surfaces that are fractured in an uneven pattern, which is clearly exhibited under a polarized microscope used in optical mineralogy. Crystal habit of Bastnasite mineral usually includes small hexagonal rounded flakes and short prismatic crystals that are splendidly exhibited under a polarizing light microscope for mineralogists. Prismatic crystals of Bastnasite mineral specimens are usually found in shapes like slender prisms. It can be also found in rosette formations and also in spheres. Bastnasite crystals are usually found in tabular to equant in shape, which are commonly displaying interesting microscope views both transmitted and reflected light of petrographic polarizing light microscope used in optical mineralogy. They can be also found in massive and granula form. Bastnasite minerals can be also found as compact and earthy masses. Mineral Bastnasite is actually known to replace the crystals of mineral Allanite.

 

            Mineral specimens of Bastnasite are usually found in shades of white, tan, brown, gray, pink and yellow in both transmitted and reflected light of petrographic polarizing light microscope used in the field of optical mineralogy. They may also appear in wax yellow, honey yellow, reddish brown, or pale yellow to colorless. Bastnasite mineral specimens usually exhibit variations of luster in the reflected light of petrographic polarizing light microscopes for mineralogists. Luster may appear pearly on basal partings, vitreous, or greasy to dull in reflected light of polarized microscopes used in the field of optical mineralogy. The cleavage found for mineral Bastnasite is commonly in four directions. When mineral specimen of Bastnasite is evaluated between crossed nicols of polarizing light microscope used in optical mineralogy, it has distinct or basal cleavage found in one direction and poor prismatic cleavage in the other three directions. It has uneven fracture found when viewed with several adjustments on the aperture diaphragm petrographic polarizing light microscopes for mineralogists. Fracture describes how a mineral breaks when broken contrary to its natural cleavage planes. The hardness measure for the mineral Bastnasite using the Mohs scale method is commonly found ranging from 4 to 4.5. The specific gravity measure of Bastnasite usually gives values ranging from 4.7 to 5.0 grams per cubic centimeters, which is considered well above average. When Bastnasite mineral specimen is rubbed on a white streak plate, it usually leaves a white streak.

 

            When specimen of mineral Bastnasite is evaluated between crossed nicols of petrographic polarizing light microscope used in the field of optical mineralogy, it can be found as a uniaxial positive figure. It has faint pleochroism under polarized light microscope for mineralogists. Mineral Bastnasite is used in glass polishing. This is because Bastnasite minerals offer a low cost to obtain the necessary amount of cerium in polish compounds. This mineral Bastnasite can be also consumed in television faceplates and light bulbs for ultraviolet shielding and de-coloring. After series of chemical evaluations, Bastnasite minerals are found having different radioactivity. Bastnasite-(Y) is found as non-radioactive mineral. Bastnasite-(Ce) on the other hand is considered as a radioactive mineral. Crystals of Bastnasite are commonly found horizontally striated and also maybe elongated. Parting found when Bastnasite mineral specimen is evaluated between crossed nicols of polarized microscope used in the field of optical mineralogy. Bastnasites are commonly known to be strongly piezoelectric and usually have dark red cathodoluminescence.

 

            Bastnasite minerals are commonly associated with other interesting minerals such as albite, monazite, aegirine, analcime, hematite, rutile, amphiboles, calcite, cordylite, rhodochrosite, apophylite, galena, ancylite-(Ce), fluorite, cordylite, donnayite, ashcroftine, apatite, zircon, and many other minerals. Bastnasite minerals commonly occur as crusts on weathered cerite ore. They commonly form in granite and alkali syenites and pegmatites and also in carbonatites. They can be also found in some contact metamorphic deposits but rarely as a detrital mineral in placers. The best field indicator of Bastnasite mineral usually includes color, crystal habit, specific gravity, cleavage, locality, and luster. Mineral Bastnasite is considered as a rare mineral that never had great concentrations. This remains a fact even though Bastnasite mineral is considered as one of the more common rare earth carbonates. Bastnasite mineral has notable occurrences in type of localities that include the karst bauxite deposits in Hungary, the Balkans and in Greece. It can be also found in some carbonatites, a considerably rare carbonate igneous intrusive rock found at Fen, Norway; Kangankunde, Malawi; Bayan Obo, Mongolia; the Mountain Pass, California in the United States; and Kizilcaoren, Turkey. There is also possible occurrence of Bastnasite minerals in the unusual granites of the langesundsfjord area in Norway; Mont Saint-Hilaire mines in Ontario Canada and in the Thor Lake deposits, Northwest Territories, Canada. There have been reported occurrences of Bastnasite in some hydrothermal sources.



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Monday, November 30th, 2009 at 4:35 am
Category:
The Carbonates and Borates Mineral Class
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