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Biaxial indicatrix

Biaxial indicatrix. Similar to Nesse, Fig. 7.1a. Biaxial indicatrix. Similar to Nesse, Fig. 7.1b. Orthorhombic Minerals. blue = crystallographic axes red = indicatrix axes. a ≠b ≠c a = b = g =90 ° Any indicatrix axis can correspond to any crystallographic axis e.g. a=X a=Y b=Y b=Z

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Biaxial indicatrix

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  1. Biaxial indicatrix Similar to Nesse, Fig. 7.1a

  2. Biaxial indicatrix Similar to Nesse, Fig. 7.1b

  3. Orthorhombic Minerals blue = crystallographic axes red = indicatrix axes a≠b≠c a=b=g=90° Any indicatrix axis can correspond to any crystallographic axis e.g. a=X a=Y b=Y b=Z c=Z c=X Similar to Nesse, Fig. 7.10a

  4. Monoclinic Minerals blue = crystallographic axes red = indicatrix axes a≠b≠c a=g=90° b≠90 ° Any indicatrix axis corresponds to the b crystallographic axis example shown here: b=Y Similar to Nesse, Fig. 7.10b

  5. Monoclinic Minerals blue = crystallographic axes red = indicatrix axes The angles of the other two indicatrix axes are described relative to the closest crystallographic axis e.g. Z ^ c = +15° (it’s positive if the indicatrix axis falls within the obtuse angle between a and c axes) and X ^ a = -5 ° (it’s negative if the indicatrix falls within the acute angle between a and c axes). Similar to Nesse, Fig. 7.10b

  6. Triclinic Minerals blue = crystallographic axes red = indicatrix axes a≠b≠c a≠b≠g≠90° Indicatrix axis are not parallel to crystallographic axes except by chance. Similar to Nesse, Fig. 7.10c

  7. Acute bisectrix (Bxa) interference figure http://www.brocku.ca/earthsciences/people/gfinn/optical/222lect.htm http://edafologia.ugr.es/optmine/xplconos/pttfd10w.htm

  8. Biaxial Isochromes • bands with same interference color showing regions of equal retardation – form a figure 8 around optic axes • similar to Figure 7.12 in Nesse

  9. Determining vibration directions and indices of refraction of light passing through biaxial mineralMethod 1 – similar to method for uniaxial minerals Figure 7.4a in Nesse

  10. DeterminingBiaxial Isogyres similar to Figure 7.13a in Nesse

  11. Determining vibration directions of light passing through biaxial mineralMethod 2: Biot-Fresnel Rule Figure 7.5 in Nesse

  12. Vibration directions projected onto interference figure similar to Figure 7.13b in Nesse

  13. Location of isogyres in acute bisectrix (Bxa) figure(small 2V angle) similar to Figure 7.15 in Nesse

  14. Location of isogyres and isochromes in Bxa figure(large 2V angle) similar to Figure 7.16 in Nesse

  15. NA = 0.85 Estimate of 2V angle in Bxa figure • By looking at how far the isogyres split apart with the optic plane oriented at 45 degrees NE-SW, you can estimate the 2V angle. • Fig 7.29 in Nesse

  16. Centered optic axis figure(2V large enough that other optic axis is out of view) similar to Figure 7.18 in Nesse

  17. Centered optic axis figure(2V large enough that other optic axis is out of view) similar to Figure 7.18 in Nesse

  18. Estimating 2V angle in optic axis figure • Orient optic plane to 45 degrees NE-SW and look at degree of curvature of isogyre. • Figure 7.32 in Nesse

  19. Obtuse bisectrix figure similar to Figure 7.19 in Nesse

  20. Obtuse bisectrix figure Isogyres move away after relatively small amount of rotation (~5-15 degrees) of stage. similar to Figure 7.19 in Nesse

  21. Optic normal figure (flash figure) similar to Figure 7.20 in Nesse Similar figure to uniaxial flash figure (optic axis also parallel to stage).

  22. Optic normal figure (flash figure) similar to Figure 7.20 in Nesse Typically isogyres leave the field of view in <5 degrees of stage rotation

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