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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

In the field of optical mineralogy, a small chip of rock or mineral is sampled, or a thin slice that is a few millimeters thick is cut from the specimen using a diamond saw. The chip or slice is ground flat and smooth on one surface using progressively finer abrasive, e.g. carborundum powder, starting with 80 grade and finishing with 600 grade. The smooth surface is usually cemented to a glass (usually 3×1 inch, but 2×1 inch for universal stage work) using Canada balsam or Lakeside 70 cement. Other cements are only occasionally used. The other surface is usually ground down until the rock section is 0.03 mm thick. Progressively finer abrasives are used as the section becomes thinner is gauged by observing the interference colors of common minerals such as quartz or feldspar. After cleaning excess cement from the section, it is covered with a glass cover-slip cemented on with Canada balsam.

 

            The details on thin section preparation depends also on the equipment available. Some sophisticated machines enable sections to be made almost automatically and very quickly. There can be also some successful sections that can be made by hand, the grinding being done slowly on glass plates. Indeed, sections of delicate specimens may have to be made in this way. Some poorly consolidated rocks may require impregnating with a cement before section can be made. Heating the specimen in Canada balsam is sometime sufficient, but stronger cements are available. Canada balsam is usually thinned with xylol to ease spreading. The mounting of the section is done on a hot-plate which serves to drive-off the xylol and harden the cement.



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Tuesday, December 29th, 2009 at 2:46 pm
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Optical Mineralogy
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Click Here For Best Selection Of High Quality Polarizing Microscope