Take Home exam: Geology 2311, November 5, 2008Due November 10, 2008Type your answers 1. Stibnite is a mineral described in the mineral database of your DVD. Can you answerthe following questions about it?a. How many 2-fold axes are there?b. It says that a=11.229Å, b = 11.31 Å c=3.839 Å. What does that mean?c. What is the volume of the unit cell?d. The cleavage is perfect {010}? How many cleavages is that? How do you know? Show your work.e. It commonly forms dipyramids {111}. Where would the (111) face cut the a, b and c axes?Value 25 points.2. Refer to Chapter 3 of your textbookThe title of this chapter is crystal chemistry. Why is this chapter important in mineralogy? Answer this with respect to:a. Physical Properties of Mineralsb. Structures (and formulas) of silicate mineralsValue 20 points3. The following is a TX diagram. Answer the following questions.a. A rock made up of 70% A 30% B would begin to melt at what temperature? At what temperature would it finish melting? Why?What is the eutectic temperature? How many degrees of freedom do we have here?a. 4. ?Value 10 points5. It is not unusual to get dispersed elements (ions) in minerals, for example Sr is commonly found in plagioclase.a. In plagioclase, what element is Sr replacing? How do you know? How could you predict this? Show all your work.b. When I was a graduate student, part of my duties was to do microprobe analysis (I was a trained technician) for other members of the department. One of myfellow graduate students was trying to analyze orthoclase, and he could not get totals any higher than 96%. I said I would give it a try. The elements for which I routinely analyzed were Ca, Mg, Al, Fe, Si, Ti, K, Na, and Mn. I too was unsuccessful. I ran an energy scan to look for other elements and found the presence of Ba. When I did aquantitative analysis, I discovered that the mineral contained 4% BaO. The analysis also showed that I had more Al2O3 in the mineral than predicted from the stochiometric formula. Why was this? Can you tell me what is going on here? Could I have predicted it?Value 15 points6. How much K2O is in biotite that has a Fe/Mg ratio of 1:1? Show your work.Value 5 points7. Chapter 8 of your textbook covers bonding and packing in minerals. Write an essay, using mineral examples, of why understanding bonding in minerals is important in mineralogy..Value 10
View Full Document
Unlocking...