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1. Biaxial optics Nesse, 1991
Chapter 7, page 77 to 108
3. Biaxial Minerals Minerals in orthorhombic, monoclinic and triclinic
specify length of unit cell along all three crystallographic axes
Also specify three indices of refraction
named a, b, and g (in book called na, nb and ng)
Where na < nb < ng
so maximum birefringence is ng- na
4. Biaxial minerals 3 indices of refraction: na < nb < ng
Light still broken into two rays, one fast & one slow
Both rays are extraordinary
Slow ray is always ng’, with ng > ng’ > nb
Fast ray is always na’, with na < na’< nb
6. Biaxial Minerals
X-Y,
X-Z, and
Y-Z plane
7. Biaxial Minerals The biaxial indicatrix has 2 circular sections with radius nb
The 2 optic axes (O.A.) are perpendicular to these circular sections
The angle between the 2 O.A.’s is called 2V
Axis bisecting acute angle is acute bisectrix or Bxa
Axis bisecting obtuse angle is obtuse bisectrix or Bxo
8. Optic Sign?
24. Determining the optical properties of an oriented mineral.Section (100), (010), and (001)
28. Now you know which optical direction is parallel to the a, b, and c-axis
With your interference figure you can estimate the 2V.
Draw all the information on a block diagram