Conoscopic interference pattern: Difference between revisions

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:''This page is about the geology/optical mineralogy term. For general information about interference, see [[Interference (wave propagation)]] or [[Interference pattern]]s''.

A '''conoscopic interference pattern''' or '''interference figure''' is a pattern of rings[[Birefringence|birefringent]] causedcolours crossed by dark bands (or "isogyres"), which can be produced using a [[Geology|geological]] [[petrographic microscope]] for the purposes of mineral identification and investigation of [[Optical mineralogy|mineral optical interferenceand observedchemical properties]]. The figures are produced by optical interference when diverging light rays travel through a optically non -isotropic substance. It- that is, theone bestin waywhich to determinethe if asubstance's [[mineralrefractive index]] isvaries uniaxialin ordifferent biaxialdirections andwithin alsoit. forThe determiningfigure opticcan signbe andthought opticof as a "map" of how the birefringence of a mineral would vary with viewing angle inaway [[opticalfrom mineralogy]].perpendicular Theto observedthe interferenceslide, figurewhere essentiallythe showscentral allcolour possibleis the [[birefringence]] colorsseen atlooking oncestraight down, includingand the extinctionscolours (infurther from the centre equivalent to viewing the mineral at ever increasing angles from perpendicular. The dark bands calledcorrespond isogyresto positions where optical extinction (apparent isotropy) would be seen. In other words, the interference figure presents all possible birefringence colours for the mineral at once.

Viewing the interference figure is a foolproof way to determine if a [[mineral]] is optically uniaxial or biaxial. If the figure is aligned correctly, use of a [[sensitive tint plate]] in conjunction with the microscope allows the user to determine mineral ''optic sign'' and ''optic angle''.

In [[optical mineralogy]] a [[petrographic microscope]] and cross-[[polarized light]] are often used to view the interference pattern. This is done by placing a [[Bertrand lens]] (Emile Bertrand, 1878) between a high-power microscope objective and the eyepiece. The microscope's condenser is brought up close underneath the specimen to produce a wide divergence of polarized rays through a small point. There are many other techniques used to observe the interference pattern.

In [[optical mineralogy]], a [[petrographic microscope]] and cross-[[polarized light]] are often used to view the interference pattern. The microscope's condenser is brought up close underneath the specimen to produce a wide divergence of polarized rays through a small point. This is done by placing a [[Bertrand lens]] (Emile Bertrand, 1878) between a high-power microscope objective and the eyepiece. The microscope's condenser is brought up close underneath the specimen to produce a wide divergence of polarized rays through a small point. There are many other techniques used to observe the interference pattern.

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.