You will have 50 minutes to complete this 100 point exam. Please use your time accordingly. Use the space beneath the question, or the back of the facing page to answer questions. Show your work where possible. For essay and short answer questions use concise but complete sentences and paragraphs, and good grammar. Use no notes or texts, and ask questions only of the proctor.
1) 15 pts. Describe the functions of the petrographic microscope. This answer should be much more than a simple list of parts, and should address issues related to mineralogy and petrology.
2) 10 pts. How are colors produced in nature? How are they quantified and in what ways are they important in optical mineralogy?
3) 10 pts. What is double refraction? How does it vary in minerals? How is it quantified?
4) 10 pts. As Chief Planetary Field Scientist on the U.S. Star Explorer H.J. Simpson, you must oversee the analysis of materials collected by a remote probe. Preliminary work is done by microscope, followed by tricorder studies. The first tests are to establish the nature of the thick blanket of atmospheric dust. What optical tests would you have your technical staff do to confirm that the dust is the relatively harmless mineral quartz?
5) 5 pts. Draw and label the parts of a uniaxial interference figure for a crystal with the c-axis inclined 15 degrees to the SW. Draw and label the two vibration directions for a point in the NE sector.
6) 5 pts. A standard thin section is 0.03 mm thick. In such a section an unknown mineral displays retardation colors up to first order red. What is the birefringence of this mineral?
7) 5 pts. What produces the variation in color seen in isochromes?
8) 5 pts. Sketch the indicatrix section for a uniaxial positive mineral and light transmission normal to the c-axis. Label the two vibration directions and the c-axis.
9) 5 pts. What are the isogyres and how are they formed?
10) 10 pts. Fill in blanks with best answer.
b) As above. What is the index of refraction? _________________
c) When focusing the microscope up above the specimen the Becke line moves _____________ the medium with the higher index of refraction.
d) A birefringence of ____________ would yield a retardation of 200 nm in standard section (0.03 mm thick).
e) For apatite (a tetragonal mineral) oriented with the c-axis parallel to the stage, what type of interference figure would be seen? __________________
1. 425 nm
2. 580 nm
3. 425 mm
4. 580 mm
5. 580 fm
b) Glasses have no long-range crystallographic order and are thus:
1. optically negative
2. optically positive
3. optically anisotropic
4. optically isotropic
5. optically biaxial
c) The magnifications available on typical student microscopes are:
1. 40, 100, 400
2. 40, 400, 1000
3. 4, 40, 400
4. 4, 100, 400
5. 10, 100, 1000
d) A retardation of 200 nm would yield an interference color of:
1. yellow (green)
2. green
3. gray (white)
4. red (purple)
5. black
e) Working distance in microscopy refers to:
1. Distance between eye and ocular.
2. Distance between ocular and objective.
3. Distance between condenser and specimen.
5. Distance between microscope and seat.
13) 5 pts. True or false.
b) Hexagonal minerals should have anisotropic optical properties.
c) Dispersion would account for the birefringence seen in diamonds.
d) Pleochroism would account for the change in color of biotite when the microscope stage is rotated.
e) The ocular lenses are rotated in and out to change magnification.