Homework #4 - (2 Imagine you are constructing a thin...

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Exercise #4 Due BEFORE CLASS on October 13, 2010 Rules: You may use any reference you would like. You are encouraged to help each other, but please write your own answers. Remember, no late work is accepted. Please – clearly identify your answers (circle them). - staple your pages together if you have more than one page. (1) For the following list of minerals, calculate the maximum birefringence ( δ ), the maximum retardations ( ), and the highest interference color possible assuming you observe these minerals in a standard thin section (30 μm). Be sure to give units where appropriate. The index of refraction (n) is given for the isotropic minerals. The maximum (N) and minimum (n) indices of refraction are given for the anisotropic minerals. Forsterite N = 1.712; n = 1.674 Almandine n = 1.830 Sillimanite N = 1.677; n = 1.657 Enstatite N = 1.663; n = 1.653 Muscovite N = 1.599; n = 1.560 Quartz N =1.553; n = 1.544 Calcite N = 1.658; n = 1.486 Halite n = 1.544
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Unformatted text preview: (2) Imagine you are constructing a thin section and you find a quartz grain cut parallel to the c axis that shows an interference color of first order reddish ( ∆ ~430nm). What is the thickness of this thin section? You continue to grind the thin section for another half hour and look again. The grain now has an interference color of light gray ( ∆ ~240nm). What is the thickness now? Are you happy about the quality of your thin section? Why? (3) Draw a uniaxial indicatrix: a) indicate on the drawing the location of the principal section, the circular section and one random section; b) draw these three sections next to the drawing of the indicatrix and label the ε , ε ’, and ϖ vibration directions; c) indicate if your indicatrix is for an optically positive or negative mineral? (4) Briefly describe the angular relationship between the crystallographic axes and the indicatrix axes for both uniaxial and biaxial minerals. 1...
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