Mineralogy and Petrology I Geology 2311Midterm: 1 hourOctober 27, 1999Name _______________________________Answer five of the following seven questions. Each question is worth 10 points. If you spend an averageof one minute per point on each question, you will have 10 minutes left to check your work. Please timeyourself.1. The most important group of rock-forming minerals are the silicates. They are classified into 6 groupson the basis of crystal structure. Describe this classification making sure that you use both examples anddiagrams. What are some generalities that can be made about the physical properties of these classes.2.. Write an essay on solid solution. Your answer should include what it is, what determines if it takesplace, the different kinds of solid solution, what physical properties change with solid solution, and ifappropriate examples of the above.3. Identify the following mineral from its chemical composition.Weight % Molecular weightK2O 47.1 94.2Al2O3 38.4 101.96SiO245.3 60.09H2O 4.5 18Please show all your work. What kind of silicate is this? Where might you expect to find it in nature?4. Using a P-T phase diagram, explain polymorphism using an example (it could be hypothetical).Describe three kinds of polymorphism, and give an example of each.5. Philstevite is a reddish-blue mineral that commonly occurs as a square prism terminated by a pyramidon one end and a pedion on the other. Its cell parameters are: a = 5; c= 20. Draw this crystal. To what crystal system does this mineral belong ?( You don’t need a table of symmetry to figure this out. At what distances will the (221) face cut the crystal axes?6. Describe and/or draw the following forms. Give the Miller Index of the form. Give an example of amineral that shows this type of form.a. Hexagonal prismb. Basal Pinacoidc. Octahedrond. Dodecahedron7. What is Braggs Law and how do we use it in mineralogy? Describe how you would identify an unknown mineral using the Xray diffractometer. Try to bespecific as possible. Use an example (you can make one
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