You will have 50 minutes to complete this 100 point exam. Allocate your time accordingly. Use concise yet grammatically correct English, and mentally outline your answers before beginning. Show work for partial credit.

1) 15 points. The colors seen in the petrographic microscope are routinely use in the evaluation of the compositional and crystallographic characteristics of materials. Colors are produced by dispersion, absorption, and interference. Discuss the nature of each and how it is applied to optical studies of crystalline materials.

2) 15 points. What is refraction? Discuss the complexity of refraction in different types of anisotropic crystalline materials?

3) 10 points. As senior science advisor to the LSU Baseball Team you are required to identify a finely crushed sample. The material under study is an impurity found in the irrigation water supply. Engineers suggest several possible sources that you should eliminate based on a petrographic reconnaissance: 1) glass fibers from the pipe insulation, 2) calcite from Zebra mussel shells attached to the river intake system, or 3) quartz sand used in filtering out nasty brown stuff from the river. Given that you must only determine which of the three possible contaminants is involved - how would you do this as quickly as possible using your trusty petrographic microscope.

4) 5 points. Describe the production of color seen in the isochromes of interference figures?

5) 5 points. Why use conoscopic illumination to produce interference figures?

6) 5 points. Given: nF=1.565, nD=1.553, nC=1.550, which, if any, of the following are known. In this case what are their values and units of measure? {Index of refraction, flavor, optical conductivity, dispersion, birefringence, optic sign, pleochroism, and retardation}

7) 5 points. Sketch the indicatrix cross-section for a biaxial positive crystal viewed such that light propagation is parallel to the Y direction. Label directions and indices of refraction.

8) 5 points. Sketch the interference figure for a uniaxial crystal with c-axis inclined 30 degrees from normal and towards the SE. Label one set of vibration directions.

9) 5 points. Sketch the optic axis interference figure for a crystal with 2V=60 degrees and Y oriented NE-SW.

10) 5 points. What optical properties do noncrystalline materials have?

11) 5 points ABC Oil Company is concerned about loss of permeability in several local wells. Cuttings from the wells contain a fine white encrustation that you must identify optically. The fine crystalline material displays second-order yellow retardation in grains that are about 0.04 mm thick. What is the birefringence?

12) 20 points. Very short answers.

a) Focusing up the Becke line moves ____________ the media with higher index of refraction.

b) The color red occurs at wavelengths near ______________.

c) Birefringence of 0.02 would require a thickness of ______________ in grains that display retardation of 600 nm.

d) For quartz oriented with the c-axis parallel to the stage a ____________ interference figure is seen.

e) Polarization is produced by _______________ and ______________.

f) _______________ is the result of variable absorption.

g) In an interference figure the ______________ represents zones of local extinction.

h) The Bertrand lens focuses on the accessory plate (T or F).

i) Our ability to produce higher magnification is only limited by how big a lens we can produce or how many small lenses we can place in a series (T or F).

j) Biaxial minerals may appear similar to uniaxials when 2V= ______.