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GEOL 211 Mineralogy
November 14, 2000
Second Midterm Exam

(15) 1. Give concise definitions for the following terms:

a. Mineral -

b. Perthite -

c. Chatoyancy -

d. Exsolution -

e. Luster -

(15) 2. a. Briefly explain how and why mineral hardness is related to crystallographic and compositional characteristics of a mineral.

b. Color is a measure of what characteristics of a mineral?

c. Density is a result of which two aspects of a mineral (on an atomic scale)?

(5) 3. Briefly compare and contrast displacive and reconstructive mineralogical transformations.

(15) 4. Indicate which of the following statements which are FALSE or unlikely, or fill in the blanks:

a. _______________ is a common alteration product of mafic minerals.

b. b-quartz is distinguished from a-quartz by its stubby prismatic form.

c. Stishovite is a low-pressure polymorph of silica.

d. Mica is an example of a 2:1 phyllosilicate.

e. Ca2+ and Fe2+ are two ions that commonly substitute for each other in minerals.

f. It is possible for two amphiboles to coexist at equilibrium with one another.

g. The peristerite gap is a region of immiscibility in the plagioclase mineral series.

h. A silicate mineral which consists of isolated silica tetrahedra bonded together by metal ions is called a _______________.

i. Crystallographic anisotropies result in anisotropies in other characteristics of a mineral (e.g., its hardness, electrical conductivity).

j. The state mineral of Idaho is called the _______________.

k. _______________ is an amphibole found in rocks that formed under conditions of high pressure and relatively low temperature.

l. Epidote, chlorite and actinolite are three minerals that contribute to the "green" color of Greenshists.

m. Amphiboles are distinguished from pyroxenes on the basis of their lack of cleavage.

n. The most abundant mineral in the earth's crust is _______________

o. Minerals containing (OH)- are referred to as _______________ minerals.

(10) 5. a. Briefly describe the basis for the chemical classification of minerals.

b. A silicate has the following structural formula: XY5Z4O10(OH)2. What type of silicate is it? Briefly explain your reasoning. (Note: X=10-fold site; Y = octahedral site; Z = tetrahedral site).

(15) 6. Indicate which of the following are unreasonable mineral assemblages (circle the assemblages that are unreasonable, and briefly explain your reasoning):

a. A coarse grained, equigranular rock consisting of quartz + anorthoclase + oligoclase + biotite.

b. A volcanic rock consisting of leucite + quartz + biotite + sanidine.

c. A coarse grained rock consisting of bytownite + augite (pyroxene) + olivine.

d. A coarse grained rock consisting of nepheline + microcline + riebeckite + oligoclase.

e. A volcanic rock consisting of oligoclase + sanidine + bytownite + quartz + biotite.

(10) 7. (a) Make a cross-sectional sketch of a 2:1 phyllosilicate showing the arrangements of T- and O-layers, and the locations of the interlayer sites.

b. Describe why the smectite clays are expansive and have a high capacity for chemical interactions with their surroundings, in comparison to other phyllosilicates.

(15) 8. Refer to the following diagram.

(a) Plot a point on the diagram corresponding to a bulk composition of XAn = 0.6 and T = 1000oC.

(b) Use the diagram to determine the chemical composition of plagioclase (in terms of XAn) under the conditions specified in part (a).

XAn = ______________

(c) Use the diagram to determine the proportions of liquid and crystals present under the conditions specified in part (a).

Amount of liquid (%) = _____________

Amount of mineral (%)= _____________


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