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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

Take for example a thin section of quartz cut at right angles to its c-axis. Then the sample is placed in convergent polarized light of petrographic polarizing microscope used in optical mineralogy. The rays of light pass through the section at oblique angles and are polarized into two rays. The ordinary rays must vibrate in the plane of the section, which is the circular section of the indicatrix. The extraordinary rays must lie in vertical plane which contain the c-axis since they vibrate at right angles to both the ordinary ray and the travel direction of light. The vibration directions of the rays dip in towards the c-axis. All other rays of the light passing obliquely through the section are similarly polarized into two rays. In every case, the ray must vibrate in a vertical plane containing the c-axis. Therefore, in plan view, the vibration directions of the rays form a radiating pattern at the right angles to which there is a concentric pattern of the ordinary ray vibration directions. The light is usually extinguished completely and a black cross called isogyre is formed where these vibration directions are parallel to those of the polarizer and analyser of petrographic polarizing light microscope used in optical mineralogy. The black cross will not change in position when the stage of the polarized microscope for mineralogists is rotated. Outwards from the center of the figure found under the polarizing microscope used in optical mineralogy, the dip of the rays increases and with it the birefringence. Concentric rings of interference color are therefore formed, but are only clearly seen with minerals of high birefringence or in thick sections when evaluated under polarizing microscopes used in optical mineralogy.



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Tuesday, December 29th, 2009 at 2:48 pm
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Optical Mineralogy
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Click Here For Best Selection Of High Quality Polarizing Microscope