Mineral Science — DU B.Sc. (Hons.) Geology Previous Year Question Papers

3. Describe in detail different silicate structures on the basis of joining of Si04 tetrahedra and their respective Si:O ratio. Give one mineral example of each and respectivei rock type (one each) in which it is present. 4. Describe different polytypes-in muscovite with suitable illustrations. What are the geological conditions under which each is likely to be found? 5. What are symmetry elements in 3D that involve translation? Discuss with suitable illustrations. Identify the ions that occupy spercific crystallographic sites in .each of the following minerals, and indicate the corresponding crystallographic locations for t`hese ions. (a) 01ivine (b) Garnet (c) Mica (both dioctahedral and trioctahedral) (6x3= 18) 7. With suitable illustrations wherever applicable, write in .detail about the physical properties of minerals on the basis of 8. (a) Interference of light (b) Mechanical properties (c) Electrical properties (6x3=18) questions from the rest. 1. Answer the followings : (a)Minerals belonging to biaxial. system are (b) Angles between faces in the distorted crystal are the same as in the perfect crystal. This is Law Qf (6) In Moh's scale of hardness which mineral has hardness a little less than a pen knife? \The frequency with which a given face is observed is roug`hly directly proportional to the number of it contains in the lattice. (d)Mineral with 3± symmetry belongs to system and a common mineral crystallizing under this is (e) The combination of a mirror reflection with a translation component parallel to the mirror, results operation. (I) Chalcopyrite structure can be derived from sphalerite structure, by regularly substituting in sphalerite. This of the unit cell. (g) Give two examples of minerals belonging to mesosilicate group. (h) A crystal face has the following intercepts for the crystallographic.axes: 1al, 1a2, I/2a3,coo. The Miller-Bravais indices for the face is (i) Which one of the following represent a closed form? (a) Tetragonal prism @) Dihexagonal pyramid (c) Trigonal dipyramid a) Ditetragonal pyramid 0) Which one of the following is a non-pleochroic crystal system? ` (a) Hexagonal (b) Triclinic (c) Cubic (d) (k) Double reflection ph.enomenon is shown by (a) Isotropic substances `only (c) both isotropic and anisotropic substances (d) None of the above (1) Microcline shows cross hatchet appearance due to (a) Unidirectional twinning in albite law (b) Unideirectional twinning in pericline law (c) Twinning in two directions on the Albite law (d) Twinning in two directions: one on the albite law. and the other on the pericline law 2. Answer the following : (6x3=18) (a) Explain the relationship between polymoxphi§m and radius ratio? (b) Which type of minerals have anisodesmic bonds? What is its effect on physical property of minerals? (c) With examples explain isostructures and polyinorphs.