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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

Hitherto we have considered only the case of minerals, which, in section, transmit a certain amount of light. But some minerals, even in thin section, are quite opaque, and special method of investigation is employed for their identification. When using the pertological microscope, the mirror must be tilted so that no light comes from below, the tube placed vertically, and the examination should be conducted near a window or other source of light, so as to allow of reflection from the upper surface of the slide. In new or contemporary models of petrographic polarizing microscopes, the only source of light that must be used is the reflected light and the transmitted light source must be turned off. In these circumstances, magnetite shows a black metallic surface when viewed in reflected light of geological polarizing microscope if fresh. It is associated with a red alteration product, hematite, if decomposed. Ilmenite if fresh has also a black metallic appearance when evaluated in reflected light of polarizing microscopes, but decomposition results in the formation of a whitish substance, which may be arranged in triangular areas and it is often wonderfully exhibited under petrographic polarizing light microscope. But then this geometrical arrangement is not always seen. Iron pyrites shows a brass-yellow color and metallic luster.

 

            This test may also be employed with advantages in the examination of some minerals, which are not opaque. The distinction between quartz and feldspar may sometimes be made advantageously by observing the mineral in question in reflected light of the polarizing microscopes. Any alteration of the feldspar is easily seen by this method.



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Wednesday, February 13th, 2008 at 3:45 am
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Characteristics of Minerals in Reflected Light
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Click Here For Best Selection Of High Quality Polarizing Microscope