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Lecture 16 (11/20/2006) Analytical Mineralogy Part 3: Optical Properties of Biaxial Minerals

Lecture 16 (11/20/2006) Analytical Mineralogy Part 3: Optical Properties of Biaxial Minerals. Optical Indicatrices. A 3-d map of the indices of refraction for various vibration directions of light rays

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Lecture 16 (11/20/2006) Analytical Mineralogy Part 3: Optical Properties of Biaxial Minerals

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  1. Lecture 16 (11/20/2006)Analytical MineralogyPart 3:Optical Properties of Biaxial Minerals

  2. Optical 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 Anisotropic- Biaxial Orthorhombic Monoclinic Triclinic Anisotropic – Uniaxial Tetragonal Hexagonal Isotropic Isometric

  3. Biaxial Indicatrix Principal vibration axes greatest n lowest n intermediate n < ’<<’<

  4. Circular Sections and Optic Axes Circular Section Optic Plane Optic Axes Circular Section

  5. 2V and the Optic Sign Trace of Circular Sections - +

  6. Random Section through the Biaxial Indicatrix Vibration plane parallel to stage Double refraction rays

  7. Variable Birefringence within a Biaxial Mineral =0 =max

  8. Biaxial Optic Axis Figures Look for a mineral with the lowest interference colors, i.e. ~0

  9. Acute Bisectrix Figures (Bxa) Melatope (emergence of optic axes)

  10. Off-centered Bxa figure

  11. Determining the Optic Sign of Biaxial Minerals U D - + D U U D X D U + - U D X D U ’ is fast ray  is intermediate ’ is slow ray

  12. Estimating 2V by Curvature of Isogyre

  13. Estimating 2V by Separation of Isogyres

  14. Extinction Angle Parallel Inclined Symmetrical

  15. Sign of Elongation Slowing down the slow ray Interference colors increase Example – Length slow slow ray

  16. Next Lecture 11/22/06 Principles of X-ray Mineralogy Read: Klein p. 309-321

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