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GEOL 211 Mineralogy
December 14, 2000
Final Exam

(15) 1. Give concise definitions for the following terms (explain in words; do not simply give a formula):

a. Mineral -

b. Relief (optical) -

c. Becke Line -

d. Index of refraction -

e. Interference colors -

(10) 2. List and briefly describe the advantages of using an optical microscope (i.e. over hand sample techniques) for the mineralogist.

(15) 3. (a) Birefringence is a measure of what aspect(s) of a minerals properties?

(b) A mineral is said to be uniaxial positive. Briefly explain what that means in terms of a minerals optical properties.

(c) To what crystal systems may the mineral of part (b) belong? Briefly explain your reasoning.

(10) 4. Briefly describe "double refraction", and explain how it results in light interference, and ultimately in the production of interference colors when viewing a mineral under crossed polars.

(10) 5. Use the information provided to answer the questions: Andalusite--Al2SiO5; symmetry 2/m2/m2/m; forms {100} {001}; cleavage {110}; axial ratios a:b:c = 2:4:6 (NOTE: these are simplified from the actual values for clarity).

(a) Make a sketch of the mineral as it would appear (if euhedal) if viewed in the following two directions:

(b) Show cleavage traces on the respectives sketches of part (a).


(10) 6. Answer or fill/in the following questions/statements:

(a) A common alteration product of ferromagnesian silicates is the mineral ____________.

(b) Amphiboles and pyroxenes are both examples of inosilicates. (T or F)

(c) Andalusite, sillimanite and ____________are members of the aluminosilicate group.

(d) Blueschists are high-P, low-T metamorphic rocks consisting in part of the blue amphibole


(e) Unlike the alkali feldspars, plagioclase never undergoes exsolution. (T or F)

(f) ____________is an example of a cyclosilicate.

(g) The difference in hardness between corundum and diamond is about the same as that between talc and gypsum. (T or F)

(h) A type of garnet commonly found in calc-silicate metamorphic rocks is ____________.

(i) ____________is an element which might be expected to substitute for Zr in zircon (ZrSiO4).

(j) The state mineral of Idaho is called the ____________.

(10) 7. Refer to the following diagram.

(a) Plot a point on the diagram corresponding to a bulk composition of XMg2SiO4 = 0.4 and T = 1300oC.

(b) Use the diagram to determine the chemical composition of olivine (in terms of XMg2SiO4) under the conditions specified in part (a).

XMg2SiO4 =

(c) This type of olivine is called ________________.

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

Amount of liquid (%) =

Amount of olivine (%) =

(10) 8. The following are some hypothetical mineral assemblages and rock textures. Indicate which mineral assemblage is plausible/implausible. For those that you consider implausible, give a brief explain your reasoning.

(a) Augite + hypersthene + forsteritic olivine + bytownite; fine grained, porphyritic.

(b) Forsteritic olivine + ferroaugite + bytownite; basalt.

(c) Quartz + nepheline + sanidine + andesine + biotite; rhyolite.

(d) Quartz + sanidine + leucite + aegirine-augite + biotite; fine-grained, porphyritic

(e) Kaolinite + olivine + anorthite + hypersthene; unaltered basalt.

(f) Ferroaugite + enstatite + bytwonite + forsteritic olivine; coarse-grained

(g) Epidote + actinolite + chlorite; altered basalt.

(h) Quartz + microcline + muscovite + albite; coarse grained granite.

(i) Quartz + albite + hornblende + augite + labradorite; fine grained igneous rock.

(j) Quartz + ferroaugite + fayalite + anorthoclase + oligoclase; fine grained rock.

(10) 9. (a) What three physical and chemical factors define the types of minerals found in a rock at equilibrium.

(b) Briefly explain why equilibrium is often not attained in geologic systems.

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