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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

One of the features of minerals that need extra care upon identification of minerals in optical mineralogy is their structure. Twinning is one of the structures that need to be carefully evaluated and this can be done more accurately when the mineral is viewed with the aid of the petrographic polarizing light microscope. Minerals usually show twinning features and these are generally noticed by the parts of the twin that are not extinguishing at the same time. This property, just in the case of macroscopic minerals may not need to be observed between crossed nicols of polarizing microscopes. In optical mineralogy, there are several descriptions of twinning. Some of which are simple, polysynthetic that is due to repeated twinning after the same law, and crossed or gridiron that is due to repeated twinning after two laws.

 

            Another structure of minerals in optical mineralogy that needs careful investigation is the zonal structure.  The zones that are extinguishing at different times between crossed nicols of polarized microscope for geologists often make zonal structure visible. It may also be noticed by the zones being slightly found exhibiting different color under the petrographic polarizing microscope. This is also called zonal distribution of inclusions. Just for instance, in the case of the feldspar minerals, the zonal structure may be caused either by the crystal being formed of zones of different chemical composition or by ultramicroscopic twinning that can be clearly found visible when viewed with the aid of the polarizing microscope for mineralogists.

 

            Aggregate structure is also another point of description of minerals in optical mineralogy. This structure is a confused mass of separate little crystals, scales or grains, all of which are extinguishing at different times when viewed under petrographic polarizing light microscope.

 

            Sphaerulitic structure is the kind that is usually produced by the aggregation, in a radiate form, of crystals or crystallites. In optical mineralogy, this is generally easily noticed as dark cross, which results from the extinguishing of the light in those crystals having vibration direction parallel to the planes of vibration of the nicols. When the same stage of the petrographic polarizing microscope is rotated, the arms of the cross noticeably do not rotate.

 

            Pseudomorphic structure as described in optical mineralogy may be found partial or complete. And this can be noticed by the changed portions that are producing different optical effects from those of the original mineral when closely evaluated under polarizing microscope. There can be some instances in optical mineralogy wherein although the speudomorphism has been almost complete, the form of the original mineral or crystal may still be found.



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Monday, April 28th, 2008 at 3:19 am
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Optical Mineralogy
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Click Here For Best Selection Of High Quality Polarizing Microscope