Lecture 16 (11/20/2006) Analytical Mineralogy Part 3: Optical Properties of Biaxial MineralsOptical IndicatricesBiaxial IndicatrixCircular Sections and Optic Axes2V and the Optic SignRandom Section through the Biaxial IndicatrixVariable Birefringence within a Biaxial MineralBiaxial Optic Axis FiguresAcute Bisectrix Figures (Bxa)Off-centered Bxa figureDetermining the Optic Sign of Biaxial MineralsEstimating 2V by Curvature of IsogyreEstimating 2V by Separation of IsogyresExtinction AngleSign of ElongationNext Lecture 11/22/06Lecture 16 (11/20/2006)Lecture 16 (11/20/2006)Analytical MineralogyAnalytical MineralogyPart 3:Part 3: Optical Properties of Biaxial Optical Properties of Biaxial MineralsMineralsOptical IndicatricesOptical Indicatrices• A 3-d map of the indices of refraction for various vibration directions of light rays• Orientation of the indicatrix within a mineral is symmetrical with the crystallographic axisIsotropicIsotropicIsometricIsometricAnisotropic – UniaxialAnisotropic – UniaxialTetragonalTetragonalHexagonalHexagonalAnisotropic-Anisotropic-BiaxialBiaxialOrthorhombicOrthorhombicMonoclinicMonoclinicTriclinicTriclinicBiaxial IndicatrixBiaxial IndicatrixPrincipal vibration axesgreatest nnlowest nnintermediate nn< < ’<’<<<’<’<Circular Sections and Optic AxesCircular Sections and Optic AxesCircular Circular SectionSectionCircular Circular SectionSectionOptic Optic AxesAxesOptic Optic PlanePlane2V and the Optic Sign2V and the Optic Sign+-Trace of CircularSectionsRandom Section through the Random Section through the Biaxial IndicatrixBiaxial IndicatrixVibration plane parallel to stageDouble refractionraysVariable Variable Birefringence Birefringence within a within a Biaxial Biaxial MineralMineral=0=maxBiaxial Optic Axis FiguresBiaxial Optic Axis FiguresLook for a mineral with the Look for a mineral with the lowest interference colors, i.e. lowest interference colors, i.e. ~0~0Acute Bisectrix Figures (Bxa)Acute Bisectrix Figures (Bxa)Melatope (emergence of optic axes)Melatope (emergence of optic axes)Off-centered Bxa figureOff-centered Bxa figureDetermining the Optic Sign of Biaxial MineralsDetermining the Optic Sign of Biaxial MineralsDD++DD--UUUUDDDDDDDD’ ’ is fast rayis fast ray is intermediateis intermediate’ ’ is slow rayis slow ray--++XXUUUUUUUUEstimating 2V by Curvature of Estimating 2V by Curvature of IsogyreIsogyreEstimating 2V by Separation of Estimating 2V by Separation of IsogyresIsogyresExtinction AngleExtinction AngleSymmetricalSymmetricalParallelParallelInclinedInclinedSign of ElongationSign of ElongationslowslowrayrayExample – Length slowExample – Length slowInterference Interference colors increasecolors increaseSlowing down Slowing down the slow ray the slow rayNext Lecture 11/22/06Next Lecture 11/22/06 Principles of X-ray MineralogyPrinciples of X-ray MineralogyRead: Read: Klein p. 309-321Klein p.
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