Geos 306, Mineralogy

Final Exam, Dec 13, 2002

100 pts


1.     (20 pts) Sketch a diagram showing the structure of the earth. Make a table and define the boundaries of each region by

        a. depth

        b. temperature and

        c. pressure.

Include the surface and the center of the earth in your answer.

List the important mineral phases that are found in each of the different regions.

2.     (20 pts) For each illustration:

a)    Provide representative chemical formula for each, assuming composition is from Mg,Fe,Si,O space.

b)    Name the minerals whose structures are illustrated and whose chemistry matches that given in part a).











3.  (20 pts) The image provided below is an electron microscopic picture of a sample of feldspar, of bulk composition ~50% K-spar, ~30% albite, ~20% anorthite.

a.     Identify each of the 3 feldspar phases in the image.

b.    Draw the ternary diagram of the feldspars.

c.     Describe and explain their mixing properties. Provide your explanation at the atomic scale.

d.    Names each of the different phases defined by Al/Si ordering in the K-spars and in albite, including the type of temperature conditions you would expect to find these phases.

4. (10 pts) Below is a PT plot that shows the phase boundaries of the common silica polymorphs. Identify the stable phase associated with each region.

5. (20 pts) From an analysis of earthquake data, Shearer and Flanagan (1999) determined that there was a 7.3% increase in the velocity of p-waves across the 410 km discontinuity. In the laboratory, Zha et al (1996) measured a 12% increase in the sound velocity between pure Mg2SiO4 forsterite and wadsleyite at 13.7 GPa.

a.     Using this data, estimate the percentage of olivine in the mantle.

b.    It is unlikely that the Zha et al (1996) experiment was conducted under true mantle conditions. Describe 2 ways in which their experiment could be modified to provide a better picture of the real olivine composition of the mantle.




6. (10 pts) In one page or less, describe the physical nature of crystals from the atomic scale perspective. Only the portion of your answer that is on this page will be graded. Start your answer with a discussion about how we identify if a material is crystalline or not, then extend this to include symmetry, atom sizes and shapes, etc.