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The chemical formula of mineral Bertrandite is indicated by Be4Si2O7(OH)2 or Beryllium Silicate Hydroxide. Bertrandite is actually a Silicate mineral. Mineral Bertrandite was named after Leon Bertrand (1844-1909), a French mineralogist. It was first discovered in the year 1883 near Nantes, France. Berlinite is also considered as one of the more important ores of beryllium mineral, but only secondary to mineral Beryl. Aside from being an ore of the same metal, Bertrandite minerals are closely tied to the gemstone mineral Beryl. Beryl and Bertrandite minerals are commonly associated with one another. Bertrandite is actually an alteration product of mineral Beryl. Bertrandite can be found growing with Beryl crystals at some time. At some other times, Bertrandite can be found completely replacing the crystals of mineral Beryl to form a pseudomorph. In optical mineralogy, a pseudomorph is produced by the replacement of the chemistry and structure with a new mineral, but the outward shape of the original crystal is actually preserved. Some other pseudomorph is through an atom by atom replacement of one mineral for another. A pseudomorph is actually a false shape in the field of optical mineralogy. Bertrandite mineral is commonly associated with quartz, micas, cheralite, albite, fluorapatite, fresnoite, orthoclase, anatase, pyrite, calcite, brookite, analchime and top most of all of course the Beryl mineral.

 

            Specimens of mineral Bertrandite are commonly found colorless, white and pale yellow if evaluated under petrographic polarizing light microscope used in the field of optical mineralogy. They are most commonly found colorless in thin sections. In the field of optical mineralogy, it has been known that colorless mineral specimens actually allow the whole constituents of the white light to pass through making the mineral non-pleochroic even between crossed nicols of petrographic polarizing light microscope for mineralogists. They are also most commonly found exhibiting vitreous to pearly luster when closely viewed in reflected light of polarizing microscope used in the field of optical mineralogy. Bertrandite is most commonly found showing good cleavage in one lengthwise direction when specimen is viewed between crossed nicols of polarizing light microscope used in the field of optical mineralogy. Sometimes it can be also found perfect. It also usually found showing uneven to conchoidal fracture under several adjustments on the aperture diaphragm of the petrographic polarizing microscope used in the field of optical mineralogy. The hardness measure of mineral Bertrandite when it is evaluated using the Mohs scale method is usually found ranging from 6 to 7. Bertrandite is most commonly found leaving a white to gray streak when mineral specimen is rubbed on a white steak plate. The specific gravity measure of Bertrandite mineral is commonly found ranging from 3.3 grams per cubic centimeters to 3.5 grams per cubic centimeters. Bertrandite crystals are usually found brittle, a property commonly displayed by glasses and most non-metallic minerals.

 

            Mineral Bertrandite is known to crystallize in the orthorhombic system of crystal formation. In the field of optical mineralogy, this crystal system comprises crystals having three mutually perpendicular axes, of which all are of different lengths. Crystal of Bertrandite is usually found transparent to translucent in appearance. The crystal habit of Bertrandite as described in the field of optical mineralogy usually includes tabular to platy crystals and sometimes in prismatic forms, which can be very interesting when viewed with the aid of geological polarizing light microscopes. Tabular forms are crystals that are shaped like a book and this is usually very nice when viewed under polarized microscope for mineralogists. The dominant faces of prismatic crystals are those of a prism and this can be seen clearly visible when evaluated with the aid of petrographic polarizing light microscopes used in the field of optical mineralogy. They are also often found as aggregates formed over crystals of Beryl. Pseudomorphs of Bertrandite are also commonly found. It commonly shows lamellar, parallel growth of individual crystals.

 

            Bertrandite mineral crystals are commonly found having biaxial negative figure when viewed between crossed nicols of polarized microscope used in optical mineralogy. Crystals of Bertrandite mineral are commonly twinned and these twinned crystals are usually interesting to view under polarizing microscopes for mineralogists. Twinned sections can be seen clearly visible between crossed nicols of geological polarizing light microscope. A possible sequence of polysynthetic twinning can be also found. Often times, twins are found as heart shaped and these are seen clearly visible when viewed under polarizing light microscopes for geologists. Specimens of Bertrandite are usually found exhibiting fluorescent green color under ultraviolet light. When evaluated using the cobalt nitrate test, Bertrandite usually turns blue. Bertrandite crystals commonly whiten but hardly fuse on charcoal and are often found insoluble in acid. Bertrandite specimens are usually found having moderate surface relief when evaluated under several adjustments on the aperture diaphragm of the petrographic polarizing light microscope used in the field of optical mineralogy. It shows very weak dispersion when viewed in plane light of petrographic polarizing microscope for mineralogists. There is no specific data on the toxicity and health danger for mineral Bertrandite. However, specimens of this mineral should be treated with great care and use of sensible precaution is advised upon handling them.

 

            Bertrandite mineral is commonly found in beryllium bearing pegmatite rocks and also in some hydrothermal veins. It is also considered as a secondary mineral, which is mostly formed from late post-deposition hydrothermal attack on pegmatite Beryl. It can be also found as primary from lower-temperature gas deposition that is causing a rock alteration. Bertrandite minerals can be also found in fissures in granites and pegmatites and in miarolitic cavities in greisens. Best field indicators of Bertrandite mineral commonly include color, hardness, cleavage, crystal habit and its splendid association with mineral Beryl. Bertrandite notably occurs in types of localities such as France, Kazakhstan, Russia, Utah, New Mexico, California, China, England, Norway, Mexico and Mongolia. Excellent small Bertrandite crystals are found in pockets in the cleavelandite feldspar at Portland, Connecticut.



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Tuesday, December 15th, 2009 at 2:49 pm
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The Silicates Mineral Class
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