This 100 minute Final Exam is worth 200 points so allocate your time based on point value and question difficulty. Do not use notes, books, or consult with anyone other than Byerly. Good luck on the exam and have a nice summer.
1) 12 pts. What is refraction? How does it vary amongst naturally occurring inorganic solids?
2) 12 pts. Phyllosilicate structures display quite a variety of stacking arrangements. Give three distinct examples and discuss how the stacking variations produce differing physical properties.
3) 20 pts. Discuss the important components of the petrographic microscope and their function. As much as possible use language and examples that would be appropriate for a non-geology audience.
4) 5 pts. The Civil Engineering Department is tuning its million-dollar ruby-crystal laser and they need to know the precise thickness of the ruby wafer. You know that ne-no of ruby to be 0.01 and that it is trigonal in symmetry. How must the wafer be oriented to use retardation in calculating thickness?
5) 5 pts. What are isochromes and how do they form?
6) 5 pts. Sketch the interference figure for a hexagonal mineral with c-axis inclined 15 degrees from vertical and towards the SE. Label vibration directions in one quadrant.
7) 5 pts. Sketch the Bxa interference figure for a mineral with 2V of 10 degrees and X oriented SE-NW.
8) 5 pts. The principle indices of refraction of an unknown mineral are found to be 1.555, 1.555, and 1.559. Sketch the XZ section of the indicatrix labeling X,Y, and Z directions, the optic axes, determine the 2V angle and the optic sign.
9) 5 pts. A thin section is 0.05 mm thick and includes many quartz grains in various orientations. If the maximun birefringence for quartz is 0.009 then what are the maximum and minimum expected retardations.
12) 30 points.
a) Focusing up the Becke line moves ____________ the media with higher index of refraction.
b) X represents the optic direction with fast/medium/slow speed.
c) Birefringence of 0.035 would yield a maximum retardation of
______________ in standard sections (0.03 mm thick).
d) For quartz oriented with the c-axis normal to the stage a
__________________ interference figure is seen.
e) When light moves from air to water the ray is bent
__________________ the surface norm.
f) Pleochroism is the result of _______________ absorption.
g) In an interference figure the ______________ represents zones of N-S and E-W vibration.
h) During dispersion light is bend at angles that are a function of
___________________.
i) The _________________ is the upper polaroid filter of the petrographic microscope.
j) The color yellow has a wavelength of approximately
________________ nm.
13) 20 pts.
a) The formula for anorthite is ___________________________ .
b) The formula for enstatite is ____________________________ .
c) The formula CaMgSi2O6 represents the mineral ____________ .
d) The formula Mg2SiO4 represents the mineral ______________ .
e) The radical Si4O11(OH) represents the __________________ .
f) Van der Waals bonds are best illustrated in the mineral ______ .
g) The common simple twin found in feldspars is
_____________ .
14) 5 pts. Plagioclase in a granite contains twins with the following extinction relations:
Left-side twins: 20, 21
Right-side twins: 11, 10
15) 20 pts.
a) Two non-equal cleavages of 90 degrees are found in the ____________ group.
b) The _______________ are dominated by a single pinacoidal cleavage.
c) Basalt contains essential augite and __________________.
d) ______________________ is the low-temperature and high-pressure facies of metamorphism.
e) _______________________ is the precusor to a metamorphic rock.
f) Deformation during metamorphism can be either
brittle or _____.
16) 5 pts. Molecular weights for silicon, iron,
and magnesium oxides are about 60, 72 and 40 respectively. If an pyroxene
has half of its octahedral sites iron, the other half magnesium, what is
the oxide weight percent for the pyroxene.
17) 5 pts. What is the stoichiometric formula for
a feldspar that is one-third Na and two-thirds K endmembers?
18) 5 pts. How are orthopyroxenes distinguished
from clinopyroxenes?
19) 5 pts. What textural criteria are used to
determine the sequence of crystallization in igneous rocks?
20) 5 pts. What are some ways that the relative
timing of heating and deformation determine metamorphic rock textures?
21) 5 pts. Cooling rate controls crystal morphology
or habit in many systems. Illustrate this.
22) 21 pts. Mystery minerals.
b) Isotropic, high dispersion, high relief, high price, lasts forever.
c) First order gray-yellow retardation, no cleavages or twinning, may have been picked-up at the beach during spring-break.
d) Perfect pinacoid, silky soft, often used on babys’ butts.
e) Pleochroic in browns, two cleavages at 120 degrees, in granite.
f) First order gray-yellow retardation, two unequal cleavages at 90, two different types of twinning: one polysynthetic, one simple both with same composition plane.
g) Non-silicate, common on the dinner table, three equal cleavages, doesn't like water.