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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 Alexandrite is indicated by BeAl2O4 or Beryllium Aluminum Oxide. Alexandrite is actually an Oxide mineral. Alexandrite is known to crystallize in the orthorhombic system of crystal formation. In optical mineralogy, this orthorhombic crystal system comprises crystals having three mutually perpendicular axes, of which all are of different lengths. Alexandrite emerged millions of years ago in metamorphic environment. It was first discovered in 1833 at the emerald mining regions near the Tokovaya River in the Ural Mountains of Soviet Union. It was named Alexandrite by the mineralogist Nordenskjold in honor to the Russian csar Alexander II (1818-1881) whose attainment to majority was celebrated at the said time of discovery.  It became the national stone of the Csarist Russia because it exhibits both green and red hues, the principal colors of the Old Emperial Russia. The Alexandrite gems became available in the market since the time the mines of the Urals in Russia became a primary source of the said mineral. When the Russian deposits of mineral Alexandrite became exhausted, the interest for the majestic color miracle decreased, more especially, when the Alexandrite mineral mined from other sources do not display the same splendid distinct color change even when viewed under a polarizing microscope. However, after the discovery of the so-called Brazilian Alexandrite in the year 1987 in a place called Hematita in Mina Gerais, Brazil, the situation changed. This Brazilian Alexandrite exhibits distinctive change in color that is very discernable to the unaided eye and most especially in reflected light of polarizing petrographic microscopes.

 

Alexandrite is a rare color-change variety of the mineral called Chrysoberyl and often displays nice and interesting very interesting images when viewed with the aid of polarized light microscope used in the field of optical mineralogy. It is considered as one of the rare gems in the world and it is most often found exhibiting fascinating brilliance when evaluated under gemological microscope. The scarcity is due to the chemical composition of the minerals. Mineral Alexandrite is basically a Chrysoberyl with a splendid capability to display distinct change of colors in different light source and most especially fascinating when viewed under polarized light microscopes used in the field f optical mineralogy. They are commonly used as gemstones in jewelry. But beautiful top quality Alexandrite is very rare. Occasionally from England, the smaller Alexandrite crystals are used in Victorian jewelry.

 

            Mineral Alexandrite possesses a very splendid and fascinating microscope image when viewed with the aid of petrographic polarizing microscope used in the field of optical mineralogy. Alexandrite crystals may exhibit soft shade of red, raspberry red, or purplish-red in incandescent light or even in light as simple as candlelight. In daylight or upon using a fluorescent light, they show green or bluish-green color. Alexandrite crystals when examined may appear in a variation of transparent to translucent appearance. Alexandrite is most commonly found exhibiting vitreous to greasy luster when mineral is viewed in reflected light of polarizing microscopes used in optical mineralogy. Alexandrite is also most often found exhibiting good cleavage in one direction and imperfect in the other direction when the mineral is viewed under polarized microscope used in the field of optical mineralogy. Alexandrite has conchoidal fracture when evaluated under several adjustments on the aperture diaphragm of petrographic polarizing microscopes for mineralogists thus, the stone will have smooth, shell-like surface when it is broken. The specific gravity measure is approximately 3.5 grams per cubic centimeters. The hardness measure of mineral Alexandrite when it is evaluated using the Mohs scale method is usually 8.5. Alexandrite is most commonly found leaving a white streak when it is rubbed on a white porcelain streak plate.

 

            Alexandrite is most commonly found showing strong absorption band in the yellow, which is clearly visible when the mineral is evaluated under polarized light microscopes used in optical mineralogy. The index of refraction found when mineral Alexandrite is viewed in plane-polarized light of polarizing microscope used in optical mineralogy is usually ranging from 1.745 to 1.759. Alexandrite also shows weak birefringence with strong pleochroism when evaluated with the aid of petrographic polarizing light microscope for mineralogists. It often exhibits elongated prismatic crystal and tabular inclusions with parallel striations, which are clearly exhibited with the aid of petrographic polarizing light microscope used in the field of optical mineralogy. Crystal fragments and loose or rounded grains can be also found when Alexandrite is examined with the aid of polarizing microscopes for mineralogists. Alexandrite minerals are commonly twinned at some angles leading to a kite-shaped or triangular form as results and are commonly clearly seen visible when viewed with the aid of polarizing microscopes for geologists. Repeated cyclic twinning of this mineral often produces pseudo-hexagonal forms that can be splendidly exhibited under polarized light microscopes used in optical mineralogy. They commonly occur in mica shcists and also in granitic pegmatites. Its splendid color change character is brought about by the small-scale replacement of alumina by the chromic oxide to form the Alexandrite variety. They commonly occur in gneiss, granite, and stream deposits.



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Tuesday, March 31st, 2009 at 7:53 am
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The Oxides and Hydroxides Mineral Class
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