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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 Cordierite is indicated by Mg2Al4Si5O18 or Magnesium Aluminum Silicate. Cordierite is actually a Silicate mineral. Cordierite was first discovered in the year 1813 in Bavaria, Germany. This mineral species was named after the Pierre L A Cordier (1777 to 1861), a French geologist. The name of the gem variety of Cordierite mineral called Iolite was actually derived from the Greek word for violet. Another source of derivation is the old name dichroite, which is actually a Greek word that means two colored rocks. This is said to be an allusion to the strong pleochroism exhibited by the gem mineral Iolite when viewed under petrographic polarizing light microscope. Cordierite 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.


            Cordierite is most commonly used as mineral specimen. Some well formed Cordierite mineral crystals can be also cut for gemstone purposes. However, this Cordierite mineral is not a very popular or well known mineral species among mineral collectors. But its gem quality crystals are known very well and are rather very popular among gemstone collectors and fanciers. Iolite is the term applied to the gemstone variety of Cordierite mineral. This piece of material is often found exhibiting an unusual blue violet color in transmitted light of polarizing light microscopes used in optical mineralogy. This color display of Cordierite mineral variety is very attractive and is commonly compared to a light blue sapphire stone with a purplish tint, which can be very splendid when evaluated under gemological microscopes. This is the reason why Cordierite is referred to as the water sapphire material.


            Cordierite is also most commonly found in shades of blue, violet, gray, brownish or colorless when viewed under petrographic polarizing microscopes used in optical mineralogy. Colorless sections of mineral Cordierite are commonly allowing the whole constituent of the white light to pass through. Cordierite is also most commonly found exhibiting a vitreous luster in reflected light of polarized microscope for geologists. Cordierite is also most commonly found showing poor cleavage found in one direction when mineral is evaluated between crossed nicols of polarizing light microscopes for mineralogists. Cordierite is also most commonly found exhibiting a subconchoidal fracture when it is examined under several adjustments on the aperture diaphragm of the petrographic polarizing light microscope. The specific gravity measure of the mineral Cordierite usually gives an approximate value of 2.3 grams per centimeter cube, which is considered light. The hardness measure of mineral Cordierite when it is evaluated using the Mohs scale method is commonly found ranging from 7 to 7.5. Cordierite is commonly found leaving a white streak when mineral specimen is rubbed on a white porcelain steak plate.


            Cordierite mineral crystals are commonly found having transparent to translucent appearance. The crystal habit of mineral Cordierite as described in the field of optical mineralogy commonly includes rare prismatic crystals but is usually massive or in compact grains embedded in metamorphic schists and gneisses. Cordierite minerals can be also found as pebbles and as grains in alluvial deposits, which can be very interesting when evaluated under geological polarizing light microscopes. Cordierite minerals are commonly found strongly pleochroic when viewed under polarized light microscopes.


Mineral Cordierite is also most commonly found showing a biaxial negative figure when viewed with the aid of petrographic polarizing light microscope used in optical mineralogy. Cordierite commonly shows a very strong pleochroism under polarizing microscopes used in optical mineralogy. Cordierite is also commonly found showing a very interesting color changing ability, which is very fascinating when examined with the aid of polarized light microscopes for mineralogists. When this Cordierite mineral is evaluated under petrographic polarizing light microscope, it can be seen when viewed in one direction that the crystal or gemstone may appear blue or blue violet. But as the crystal is rotated upon viewing under this polarizing microscope for another viewing direction, it can be noticed that the color will appear yellowish gray to light blue. Many other precious minerals may show pleochroism but most have such a small color change, which cannot be seen by the unaided eye. Other minerals may show stronger pleochroism where color change is very discernible by the unaided eye. And only a few minerals can be found exhibiting such a very strong pleochroism where color changing can be seen clearly and easily with or without any polarizing microscopes. The strong pleochroism display by Cordierite and Iolite is the reason why it is sometimes referred to as the synonym dichroite. Dichroite is a Greek word, which means two colored rock. Although mineral Cordierite is a trichroic mineral, dichroic name still persisted. The refractive indices of mineral Cordierite is commonly found ranging from 1.52 to 1.57. The indices of refraction increase with the iron content. The maximum birefringence exhibited by Cordierite under polarized microscope is usually found ranging from 0.011 to 0.018. Cordierite commonly shows low surface relief when it is evaluated under several adjustments on the aperture diaphragm of polarizing light microscope for mineralogists. Cordierite also shows weak dispersion in transmitted light of polarizing light microscope used in optical mineralogy. There is no specific data found on the toxicity and health dangers for mineral Cordierite. However, the specimens of this mineral species should be treated with great care and use of sensible precaution is advised upon handling them. Cordierite mineral is also found not radioactive after several chemical test made.


Cordierite is most commonly found associated with several other interesting minerals such as alamandine, biotite, feldspars, corundum and andalusite. The best field indicators of mineral Cordierite usually include hardness, color, density, lack of good cleavage, and pleochroism. Cordierite commonly occurs in contact or regional metamorphism of argillaceous rocks. This mineral species can be also found occurring in some pegmatites, granites and norites in gabbroic magmas. Cordierite is actually considered as a mineral of metamorphic rocks and is also considered as an indicator of intense heat. It can be also found in the granite contact zone that can be found at Geevor Tin Mine in Cornwall, England. Mineral Cordierite notably occurs at some famous mineral localities including Sri Lanka, Madagascar, Burma, India, Connecticut and Canada.

Monday, December 29th, 2008 at 6:35 am
The Silicates Mineral Class
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Click Here For Best Selection Of High Quality Polarizing Microscope