Forms of uniaxial interference figures
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This document discusses the different forms that uniaxial interference figures can take based on the orientation of the optic axis in a mineral sample. There are three main types: 1) Optic axis figures where the optic axis is vertical and the cross pattern is centered. 2) Off-centered figures where the cross is not centered and moves as the sample is rotated. 3) Optic normal figures where the optic axis is horizontal, producing a broad, fuzzy interference pattern across most of the view. Key elements like isogyres, melatope, and isochromes are also defined.
Forms of uniaxial interference figures
- 1. Forms of Uniaxial Interference Figures Prathamesh S. Pawar M.Sc. (I) Geology, Dept of Geology, S. P. Pune University
- 2. Nomenclature • Isogyres: black bars which form the cross • Melatope: intersection of the two isogyres. It is the point from where the optic axis emerges. • Colour bands are called as isochromes. Interference colours increase in order outward from the melatope, near melatope colours are low first order.
- 3. Forms or Types of Uniaxial Interference Figures • 3 types – Based on the orientation of optic axis, which is analogous the orientation of the mineral section 1. Optic Axis or Centred Figure 2. Off-Centred Figure 3. Optic Normal or Flash Figure
- 4. 1. Optic Axis Figure • aka Centered Interference Figure • The isogyres form a perfect cross • Melatope is perfectly centered • Optic axis is vertical • Interference figure for the mineral does not move as the stage is rotated
- 6. Some examples of centered uniaxial interference figures Calcite Quartz
- 7. 2. Off-cantered Figure • Cross is not centered • Melatope may or may not lie outside the field of view • Optic axis is not vertical • On rotation the melatope swings in a circle around the centre
- 8. If the Melatope is well out outside the field of view the isogyres sweep across the field of view in sequence as the stage is rotated - with the isogyres always remaining parallel to the crosshairs.
- 9. Some examples of of-centered uniaxial interference figures
- 10. 3. Optic Normal Figure • aka Flash figure • optic axis horizontal • The interference figure produced is very broad, fuzzy and occupies most the field of view
- 11. Thank You…