Conoscopic interference pattern: Difference between revisions

Revision as of 03:32, 26 September 2013

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A uniaxial mineral will show a typical 'Maltese' cross shape and its isogyres, which will revolve/orbit around a projection of the optical axis as the stage is rotated.

A biaxial mineral will typically show a saddle-shaped figure (with one isogyre thicker than the other, typically) that will often morph into totwo curved isogyres (called brushes) with rotation of the stage. The difference in these curved isogyres is known as the "2V" angle. In minerals that have far-off-center optic axes, only one part of the above sequence may be seen. On either side of the saddle the interferences rings surround two eye like shapes called melanotopes. The closest bands are circles, but further out they become pear shaped with the narrow part pointing to the saddle. The larger bands surrounding the saddle and both melanotopes are figure 8 shaped.<ref name="hartshorne">{{cite book|last1=Hartshorne|first1=N. H.|last2=Stuart|first2=A.|title=Practical Optical Crystallography|year=1964|publisher=Edward Arnold|___location=London|pages=210–211}}</ref>

A [[Interference colour chart|Michel-Levy Chart]] is often used in conjunction with the interference pattern to determine useful information that aids in the identification of minerals.