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Midterm 2 Examination Key GLY4200C Name 90 points October 26, 2011 16 took exam - Numbers to the left of the question number in red are the number of incorrect responses. Instructor comments are in blue. Florida Atlantic University MINERALOGY -- MIDTERM 2 EXAMINATION KEY True-False - Print the letter T or F in the blank to indicate if each of the following statements is true or false. Illegible answers are wrong. (1 point each) 0 T 1. All mathematical groups, including crystallographic point and space groups, must contain an identity operation. 2 F 2. All pyramidal forms are closed. 11 F 3. As nuclei grow, their surface area/volume ratio increases. 1 F 4. Growth twins are always penetration twins. 2 T 5. Low-spin Fe3+ is smaller than high-spin Fe3+. 0 T 6.As pressure increases, minerals transform to denser structures, with atoms packed more closely together 1 T 7. Although silicon normally has CN = IV, in the lower mantle the pressures are so great that the CN of silicon is VI. 2 F 8. If two ions have the same charge, the larger ion will enter a crystal structure preferentially. 2 T 9. Crystal classes are defined by the thirty-two possible point groups. 11 F 10. Possible symmetry operations include rotation axes, mirror planes, and an inversion center. What is wrong with this statement? 0 T 11. Faces composed of all anions or all cations are very high energy. They attract ions of opposite sign, grow rapidly, and may grow themselves out of existence. 1 T 12. The calculation of the zone axis is done using the same method as a vector cross- product. 1 7 F 13. When crystal field splitting occurs, the average of the energy levels of the split d orbital levels moves up or down depending on the electronic environment of the ion in question. 0 T 14. Magnetic separation based on the differing magnetic susceptibilities of different minerals is used in processing minerals since many minerals, especially those containing iron, are attracted to or repelled from a magnet in a strong magnetic field. Magnetic separation is used in both laboratory and commercial scales for mineral separation. 4 T 15. Above the Curie temperature ferromagnetic materials become paramagnetic. 10 F 16. Three d electrons give a large orbital contribution to the magnetic moment of minerals they are in. Spin, not orbital 0 T 17. Many valuable ore minerals have metallic abundances in the trace element range. 3 T 18. The blue color in minerals such as kyanite, glaucophane, crocidolite, and sapphire is the result of a ferric to ferrous charge transfer. 0 T 19. In transition metal minerals, spin contribution to magnetic moments is proportional to the number of unpaired d electrons. 1 F 20. A pinacoid is a closed form consisting of two parallel faces. 2 T 21. Ions can be arranged around a lattice point only in certain ways, which are known as point groups. 2 F 22. Isometric {100} is the same as tetragonal {100} 1 T 23. Many vectorial properties vary discontinuously as direction is changed Multiple-Choice - Choose the best response to each statement or question. Print the letter corresponding to your choice in the blank. (1 point each) 2 B 1. Minor elements are those elements whose abundances lie within what range, expressed in weight per cent? A. 1-10% B. 0.1-1% C. 0.01-0.1% D. 0.001-0.1% 2 0 A 2. What are the major elements found in the core? A. Iron and nickel B. Oxygen and silicon C. Oxygen and iron D. Silicon and magnesium 0 B 3. The minerals kyanite, andalusite, and sillimanite all have the formula Al2SiO5, but they have different structures. They may be described as: A. Mineraloids B. Polymorphic C. Polytypous D. Pseudomorphous 3 D 4. “Goethite after pyrite” is an example of what? A. Omission substitution B. Polymorphism C. Polytypism D. Pseudomorphism 3 C 5. The unit cell vector c is associated with which crystal axis? A. X B. Y C. Z D. It depends on the crystal system 7 A 6. The angle ( lies between which crystallographic axes? A. X and Y B. X and Z C. Y and Z D. It depends on the crystallographic system 1 B 7. Rotation by each step around an A4 axis is through how many degrees? A. 60° B. 90° C. 120° D. 180° 13 C 8. How many mirror planes are found in an object with symmetry 4/m 2/m 2/m? A. One How many sets of A2 axes are there? B. Three C. Five D. Nine 3 4 C 9. If a plane intercepts only one of the principal crystallographic axes, how many zeros will there be in the Miller index of the plane? A. None B. One C. Two D. Three 1 D 10. Visible light has wavelengths between 400 and 700 nanometers. What color is represented by wavelengths near 700 nm? A. Blue B. Green C. Orange D. Red 5 B 11. Which of the following forms of radiation is the least energetic? A. Gamma B. Infra-red C. Ultraviolet D. Visible 9 C 12. Moving electrical currents generate magnetic forces. What is the source(s) of magnetic force in a transition metal ion? A. Electrons orbiting the nucleus B. Electrons spinning around their own axes C. Both A and B D. None of the above 5 B 13.Which set of conditions is true for the monoclinic system? A. a … b … c, " = $ = ( = 90/ B. a … b … c, " = ( = 90/, $ … 90/ C. a = b … c, " = $ = ( = 90/ D. a … b … c, " … $ … ( 0 A 14. The most common metal in the crust of the earth is: A. Aluminum B. Calcium C. Iron D. Sodium 4 1 B 15. Interstitial substitution occurs when an atom or ion occupies space in between the normal sites. Which of the following ions would be most likely to do this? A. Al3+ B. H+ C. Mg2+ D. Si4+ 0 B 16. In point group symmetry, how many point(s) in the pattern must remain fixed? A. 0 B. 1 C. 2 D. 3 3 A 17. A symmetry operation denoted 6 is: A. A six-fold rotation followed by inversion B. A six-fold rotation followed by reflection across a plane perpendicular to the axis C. A simple symmetry operation D. Both B and C 7 B 18. The symbol [121] represents: A. Point B. Line [ ] is used for zone axis, or any line C. Plane D. Set of symmetrically equivalent planes 2 D 19. Nucleation usually requires super saturation. Which of the following might produce super saturation? A. Increasing the concentration, for example by evaporation of a solution B. Changing the temperature of a solution C. Changing the pressure of the system D. All of the above 5 D 20. Which type of twinning occurs when a preexisting crystal undergoes a change in structure due to a change in pressure or temperature A. Deformation B. Glide C. Growth D. Transformation 5 3 C 21. In this type of magnetic susceptibility class, the magnetism is due to unbalanced electron spin in the inner orbits of the elements concerned. The ionic spacing in these crystals is such that very large forces, called exchange forces, cause the alignment of all atoms to give highly magnetic domains. Which class of magnetic susceptibility is this? A. Antiferromagnetic B. Diamagnetic C. Ferromagnetic D. Paramagnetic 1 A 22. The inversion operation has as its element: A. A point B. An axis C. A plane D. None of the above 6 C 23. A 16 is the same as: A. A mirror plane B. The identity operation C. Inversion through a center D. Rotation through 180° perpendicular to the 61 axis Fill-Ins - Write in the word or words which best completes each statement or answers each question. (1 point per blank) 1-2. Abundances are most often expressed as weight per cent. Name two other systems in common use for expressing abundances. 1 1) ATOM PERCENT 2 2) VOLUME PERCENT 4 3. Using which system of reporting abundance would oxygen have a value greater than 90%? VOLUME PERCENT 5 4. The type of defect show below is known as what? STACKING ABABABCABAB 5-6 Viktor Goldschmidt described two rules, really empirical observations, governing ionic substitution. What are these rules? 9 5) CHARGE ON THE IONS CANNOT DIFFER BY MORE THAN ONE 6 9 6) FREE SUBSTITUTION OCCURS IF SIZE DIFFERS BY LESS THAN 15%, AND LIMITED SUBSTITUTION OCCURS IF SIZE DIFFERENCES BETWEEN IONS ARE BETWEEN 15 AND 30% 5 7. During crystal growth, one crystalline substance may grow on a crystalline substance of different composition and structure. Such growths are known as EPITAXIAL growths. 3 8. The ratio of induced magnetization to the strength of the external magnetic field causing the induced magnetization defines MAGNETIC SUSCEPTIBILITY . 6 9. { } is the symbol for a FORM . 2 10. Ca2+ for Na+ & void is known as OMISSION substitution. 11-13When light strikes the surface of a mineral, five different phenomena may occur. Name any three of them. 0 11. REFLECTION OR REFRACTION 0 12. TRANSMISSION OR ABSORPTION 0 13. SCATTERING OR DISPERSION Diagrams and Figures - A series of slides will be shown. Each of these is a photo or a diagram previously seen in class. Diagrams may have been altered to remove labels, etc. Answer each question as the slide is shown. (1 point each) 3 C 1. The lattice shown here is: A. C B. F C. I D. P 3 D 2. The lattice shown here is: A. C B.
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