November 20, 2001 name: ___________________GS 231: Mineralogy Second Midterm Exam1. (20 points) Native Elementsa. List six elements which correspond to minerals that are native elements.b. Why is mercury in its elemental state not included in a list of minerals?c. Name two minerals which are polymorphs and also are native elements. Describe their physicalproperties. Predict which one is stable at higher pressure and state why.2. (20 points) Carbonate Mineralsa. Give the names, formulae and crystal system of the three most common carbonate minerals that arefound in marine sediments.name formula crystal systemb. State the "aragonite problem" and give an explanation for the problem.c. Sketch the T - X phase diagram between CaCO3 and CaMg(CO3)2 and mark the region at STP.Explain why "high-Mg calcite" (say Mg20Ca80) does not survive for long even in shallowly buriedsediments, and why two carbonates can coexist in equilibrium in high grade marbles.3. (20 points) Gibbs Phase RuleBelow is an unlabeled phase diagram for Al2SiO5 including the polymorphic phases andalusite, kyaniteand sillimanite.a. (5 pts) Fill in the fields with each Al2SiO5 polymorph.b. Give the equation for the Gibbs phase rule and define each of the variables involved.c. Apply the Gibbs phase rule to the phase diagram, showing the result for the fields between thereactions, to each of the reactions, and to the triple point.4. (20 points) Oxide Mineralsa. Name two common rhombohedral oxides and give their formulae.b. Give a general formula for spinel and the coordination number for each cation site.c. Explain why the commonly used formula of magnetite, Fe3O4, is misleading in implying that thevalence of Fe is 8/3.d. Why are some oxide minerals opaque and others are transparent? Give an example of each type.4. (20 points) Phosphate Mineralsa. Give the four most abundant elements in ordinary apatite and identify the coordination numbers of thecations.b. Give a least one element that may substitute for each cation and anion group in apatite.c. Give the formulae for monazite and xenotime. One of these minerals is isostructural with a commonsilicate. Name the mineral and indicate which phosphate is isostructural with it.d. What solid solutions occur in monazite and xenotime?e. How are monazite and xenotime used to solve important geological