Lecture 16 (11/20/2006) Analytical Mineralogy Part 3: Optical Properties of Biaxial Minerals.
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Transcript of Lecture 16 (11/20/2006) Analytical Mineralogy Part 3: Optical Properties of Biaxial Minerals.
![Page 1: Lecture 16 (11/20/2006) Analytical Mineralogy Part 3: Optical Properties of Biaxial Minerals.](https://reader035.fdocuments.us/reader035/viewer/2022062714/56649d3a5503460f94a13ffa/html5/thumbnails/1.jpg)
Lecture 16 (11/20/2006)Lecture 16 (11/20/2006)
Analytical MineralogyAnalytical Mineralogy
Part 3:Part 3:
Optical Properties of Biaxial Optical Properties of Biaxial MineralsMinerals
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Optical 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 axis
IsotropicIsotropic
IsometricIsometric
Anisotropic – UniaxialAnisotropic – Uniaxial
TetragonalTetragonalHexagonalHexagonal
Anisotropic-Anisotropic-BiaxialBiaxial
OrthorhombicOrthorhombicMonoclinicMonoclinic
TriclinicTriclinic
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Biaxial IndicatrixBiaxial IndicatrixPrincipal vibration axes
greatest nn
lowest nn
intermediate nn
< < ’<’<<<’<’<
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Circular Sections and Optic AxesCircular Sections and Optic AxesCircular Circular SectionSection
Circular Circular SectionSection
Optic Optic AxesAxes
Optic Optic PlanePlane
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2V and the Optic Sign2V and the Optic Sign
+ -
Trace of CircularSections
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Random Section through the Random Section through the Biaxial IndicatrixBiaxial Indicatrix
Vibration plane parallel to stage
Double refractionrays
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Variable Variable Birefringence Birefringence
within a within a Biaxial Biaxial MineralMineral
=0
=max
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Biaxial Optic Axis FiguresBiaxial Optic Axis Figures
Look for a mineral with the Look for a mineral with the lowest interference colors, i.e. lowest interference colors, i.e. ~0~0
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Acute Bisectrix Figures (Bxa)Acute Bisectrix Figures (Bxa)
Melatope (emergence of optic axes)Melatope (emergence of optic axes)
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Off-centered Bxa figureOff-centered Bxa figure
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Determining the Optic Sign of Biaxial MineralsDetermining the Optic Sign of Biaxial Minerals
DD
++
DD
--UU
UU
DD
DD
DD
DD
’ ’ is fast rayis fast ray
is intermediateis intermediate
’ ’ is slow rayis slow ray
--
++
X
X
UU
UU
UU
UU
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Estimating 2V by Curvature of Estimating 2V by Curvature of IsogyreIsogyre
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Estimating 2V by Separation of Estimating 2V by Separation of IsogyresIsogyres
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Extinction AngleExtinction Angle
SymmetricalSymmetrical ParallelParallel InclinedInclined
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Sign of ElongationSign of Elongation
slowslowrayray
Example – Length slowExample – Length slowInterference Interference colors increasecolors increase
Slowing down Slowing down the slow ray the slow ray
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Next Lecture 11/22/06Next Lecture 11/22/06
Principles of X-ray MineralogyPrinciples of X-ray Mineralogy
Read: Read: Klein p. 309-321Klein p. 309-321