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GEOL 3010 Sample Final Exam
I. (15) Define the following: A. Mineral A mineral is a naturally occurring homogeneous solid of definite, but not fixed, chemical composition and an ordered atomic arrangement that is formed by inorganic processes.
B. Symmetry operation A symmetry operation is a transposition that leaves an object invariant.
C. Siderophile The siderophiles are those elements of the Periodic Table that form metallic bonds with Fe and are enriched in the core and in iron meteorites and depleted in the crust and mantle.
D. Birefringence The property of having different indices of refraction for light vibrating in different directions.
E. Optic plane The optic plane is the planar section of the biaxial indicatrix containing the two optic axes.
II. (6) For each of the following point-group symmetry diagrams, identify the point group (crystal class) and crystal system
A B. C.
Point Group: ____2/m_____ _____-4_______ _____622______
Crystal System:monoclinic tetragonal_____ _____hexagonal_
III.(6) Illustrated below are a set of orthogonal crystallographic axes with unit-cell tic marks. Draw on the diagram the axial intercepts of a lattice plane with Miller indices (2 0 3).
IV. (6) Identify the lattice type (P, A. B, C, I, F, or R) for each of the following:
______F________ ______A_________ _______R_______
VII. (12) Last July, some colleagues and I synthesized a sample of the mineral ringwoodite using the 5000-ton press at the Bavarian Geological Institute at Bayreuth in Germany. Ringwoodite is the high pressure form of olivine (Mg,Fe) 2 SiO 4 but unlike olivine, it can accept significant amounts of hydrogen. It is thought to be a major component of the mantle between depths of 525 and 670 km. Given below is a chemical analysis of the sample we made. Calculate the formula (Numbers of Si, Mg, Fe, and H cations per four oxygens) and its formula weight.
Oxide MolWt Oxide Wt% Moles oxide Moles Cations Moles Oxygen
SiO 2 60.086 39.82 0.66272 0.66272 1. MgO 40.312 45.89 1.13837 1.13837 1. FeO 71.846 11.46 0.15951 0.15951 0. H 2 O 18.015 2.83 0.15709 0.31418 0. 2.78040 x 1.43864 = 4.
AtWt Cations per 4 Oxygens
Si 28.087 0.9534 26. Mg 24.305 1.6377 39. Fe 55.847 0.2295 12. H 1.008 0.4520 0. O 15.9994 4.0000 63.
Formula Weight: 143.
VIII. (10) Ringwoodite is a spinel, and I measured its cubic (Z=8) cell parameter as 8.0924Å. Calculate the density of this sample.
R = (ZFW)/(A V) R = (8*143.8515)/(6.022 x 10^23 * 8.0924^3 x 10-24) R = 1150.812 / (0.6022 * 8.0924^3 ) R = 3.6061 g/cm^3
IX. (5) Ringwoodite has an index of refraction of 1.710. What is the speed of light in ringwoodite?
V = 3 x 108 / 1.710 = 1.7544 x 10^8 m/s
X. (10) Name a mineral and give the formula in each of the following groups:
A. Phosphate ___Apatite________________ Ca 5 (PO 4 ) 3 F________
B. Oxide__________Periclase______________ _________MgO_______
C. Carbonate ______Calcite_____________ _____CaCO3_____________
D. Sulfide ____________Pyrite_____________ _____FeS2______________
E. Sulfate ______Barite__________________ ____BaSO4______________
XI (10) Below is a melting (T-X) diagram for forsterite (Mg 2 SiO 4 ) – fayalite (Fe 2 SiO 4 ). Starting with a liquid of composition 80% Fo and 20 % Fa at 1800ºC (dot) answer the following questions based on the diagram assuming perfect equilibrium between crystals and solid:
A. At what temperature do the first crystals form? ___________ 1675º __________
B. What is the composition of the first crystals to form? ______ Fo 95 Fa 5 ___________
C. How many phases are present at 1600ºC? ________ 2 ________________
D. At what temperature does the last liquid disappear? ___ 1550º _______________
E. What is the composition of the last liquid to crystallize? __ _ Fo 50 Fa 50 ______________
XII. (2 extra) Circle the correct spelling: A. Mineralogy, Minerology, Minorology B. Occurance, Occurrence, Occurrance, Occurence, Ocurense, Occurrense
