What determines the lengths and angular relationship between the crystallographic axes for any particular mineral? (5) (15 points) a) Isotropic and anisotropic minerals usually display extinction differently. Briefly describe how extinction may differ between the two types of minerals. b) Explain why these two types of minerals have their characteristic extinction patterns. c) In some orientations, anisotropic minerals may have exactly the same type of extinction as isotropic minerals. Describe that orientation and explain why the mineral has the extinction that it does. (6) (15 points) Use the chart below to answer the following questions. Draw lines on the graph to show how you arrived at the answer, and then write the answer in the space available, including units where appropriate. a) From interference colors, you determine quartz (=0.009) has retardation, = 400 µm. What  is the thickness of the thin section?
What determines the lengths and angular relationship between the crystallographic axes for any particular mineral? (5) (15 points) a) Isotropic and anisotropic minerals usually display extinction differently. Briefly describe how extinction may differ between the two types of minerals. b) Explain why these two types of minerals have their characteristic extinction patterns. c) In some orientations, anisotropic minerals may have exactly the same type of extinction as isotropic minerals. Describe that orientation and explain why the mineral has the extinction that it does. (6) (15 points) Use the chart below to answer the following questions. Draw lines on the graph to show how you arrived at the answer, and then write the answer in the space available, including units where appropriate. a) From interference colors, you determine quartz (=0.009) has retardation,  = 400 µm. What is the thickness of the thin section?
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