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Click Here For Best Selection Of High Quality Polarizing Microscope

Click Here For Best Selection Of High Quality Polarizing Microscope

Having obtained the figure, the stage of the petrographic polarizing microscope should be turned so that the trace of the optic axial plane occupies an oblique position. The converging apparatus should be removed and the section examined in parallel polarized light of the polarizing microscope by means of the low power objective. Testing with the wedge, the stage of the polarized microscope remaining in the same position, will give either compensation, or will raise the polarization colors.

 

            If compensation is obtained with the optic axial plane N.E. is to S.W. using a slow wedge, then, as the length of the wedge is parallel to the optic normal, that direction must be the vibration direction of the faster ray, and the trace of the optic axial plane must be that of the slower. But the latter is the direction of the obtuse bisectrix, since the section is cut perpendicular to the acute bisectrix. Then Y, the normal, > obtuse bisectrix, that is, the obtuse bisectrix = Z. The acute bisectrix must therefore be X, and the double refraction is negative. When the double refraction is positive, compensation is obtained when the slow wedge is inserted parallel to the trace of the optic axial plane.

 

            It is possible to determine the sign of a mineral showing a biaxial figure without removing the converging apparatus. The wedge or mica plate should be inserted into the lower slot while the figure, with the optic axial plane N.W. is to S.E. or N.E is to S.W., is carefully observed. There will be one of the two effects. Either the rings will become lemniscates or the lemniscates will become rings. In the first case opposition is taking place. In the second case, it is coincidence. A process of reasoning similar to that described for the preceding method may determine the sign.



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Friday, February 15th, 2008 at 5:15 am
Category:
Mineral characters Between Crossed Nicols in Convergent
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