Download Final Examination Key - FAU Geosciences

GLY4200C
Name
108 points
December 2, 2011
16 took exam - Numbers to the left of the question number in red are the number of incorrect
responses. Instructor comments are in blue.
Florida Atlantic University
MINERALOGY -- FINAL EXAMINATION KEY
True-False - Print the letter T or F in the blank to indicate if each of the following statements is
true or false. Illegible answers are wrong. (1 point each)
3
T
1. The most common type of phase diagram for binary systems is a temperaturecomposition diagram.
2
T
2. For any angle greater than or equal to the critical angle there will be no refracted ray
– the light will be totally reflected.
8
F
3. If the refractive index is higher for at least some longer wavelengths, the material
exhibits normal dispersion.
3
T
4. Plane-polarized radiation entering an anisotropic crystal in a direction not parallel to
an optic axis, will be split into the ordinary (O) and extraordinary (E) rays, vibrating
perpendicularly.
6
F
5. The fast direction of a compensator plate is marked N. The slow direction is
unmarked, but is understood to be perpendicular.
4
T
6. The quarter 8 plate is especially useful in examining minerals showing bright
interference colors.
7
F
7. If the slow direction of the crystal is parallel to the fast direction of the accessory
plate, subtraction will occur. The new color is always less than the original color.
3
T
8. In orthoscopic mode, light rays striking a mineral grain on a thin section will be
parallel.
3
T
9. If J = 0°, a mineral will be extinct when viewed in crossed-nicols and its reference
direction is aligned with the N-S or E-W crosshair.
5
F
10. For a uniaxial negative crystal, the optical indicatrix has the shape of a prolate
ellipsoid.
1
5
F
11. The depth of focus is the range over which objects are in focus in a microscope. It
increases as the magnification increases.
4
T
12. The direction of the wave normal to the wave front obeys Snell’s Law for both the
ordinary and the extraordinary rays.
6
F
13. In a biaxial crystal, $ is the numerical average of " and (.
5
F
14. If Bxa is over Z, the mineral is biaxial negative.
2
F
15. A microscope has an objective lens whose numerical aperture is 0.70. This lens is an
oil immersion lens.
1
T
16. K$ radiation is more energetic but has less intensity the K" radiation.
2
T
17. In the Bragg equation, 2 = glancing angle of incidence.
1
T
18. K" radiation is more intense than K$ because the L to K transition is far more
probable than the M to K transition.
5
F
19. A critical angle may only exist when if nr > ni . (see Snell’s law - sin cannot be > 1.0)
2
T
20. Three component systems may be plotted on a ternary composition diagram, with both
pressure and temperature are regarded as fixed.
1
T
21. In plotting a phase diagram, it is assumed that the system is at equilibrium.
9
T
22. Inclined extinction can only occur in biaxial crystals.
3
F
23. For any angle greater than or equal to the critical angle there will be no reflected ray,
because the light will be totally refracted.
6
F
24. A crystal viewed in crossed nicols shows a white interference color. When the polarizer
is rotated to produce parallel nicols, the observed color becomes reddish. Thus the original
color was high-order white.
11
F
25. The bonding in water (H2O) is more ionic than in sylvite (KCl). (Relevant
electronegativities: Hydrogen, 2.1; Oxygen, 3.5: Potassium, 0.9; Chlorine, 2.9)
11
F
26. Ionically bonded substances are molecular, i.e. exhibit properties which may be
explained in terms of interactions between molecules.
2
1
T
27. If the bonding mechanism is not dominantly ionic, radius ratio considerations may
not be adequately used to determine the coordination number. See text, page 73
2
T
28. As nuclei grow, their surface area/volume ratio decreases.
5
T
29. Three d electrons give a large spin contribution to the magnetic moment of minerals
they are in.
2
T
30. In minerals with more than one bond type, it is common for the mineral to have
strongly directional properties. See text, page 64
Multiple-Choice - Choose the best response to each statement or question. Print the letter
corresponding to your choice in the blank. (1 point each)
0
A
1. In the formula G = H - T)S, what does H stand for?
A. Enthalpy
B. Entropy
C. Gibbs Free Energy
D. Temperature
9
B
2. A phase diagram for a unary system, such as silica, is of what type?
A. Temperature - Composition
B. Pressure - Temperature
C. Pressure - Composition
D. Pressure
5
C
3. dS/dT is:
A. Coefficient of isothermal compressibility
B. Heat capacity at constant temperature
C. Heat capacity at constant pressure
D. None of the above
5
C
4. If a system has two components, and two phases are present, how many degrees of
freedom are present?
A. 0
B. 1
C. 2
D. 3
3
2
B
5. The property determined by the equation n(8) = A + B/82 + C/84 is:
A. Birefringence
B. Dispersion
C. Refraction
D. Retardation
8
C
6. In optical mineralogy, ) is:
A. A measure of the change in the property which follows ) (i.e. )T means a change in
temperature)
B. Dispersion
C. Path difference
D. Refraction angle
3
B
7. Which of the following is not anisotropic?
A. Crystals belonging to the hexagonal system
B. Crystals belonging to the isometric system
C. Crystals belonging to the monoclinic system
D. Crystals belonging to the orthorhombic system
6
C
8. Index of refraction oils with n greater than 1.8 are often dangerous. Why?
A. They are unstable compounds which degrade with time, forming vibration sensitive
solids with a tendency to explode
B. They are highly flammable, whose vapors often catch fire
C. They contain poly-chlorinated biphenyls, compounds known to be highly carcinogenic
D. All of the above
8
C
9. In a biaxial crystal, the slowest ray travels along which optical axis?
A. X
B. Y
C. Z
D. Either X or Z, depending on whether the crystal is positive or negative
5
B
10. The index of refraction associated with the circular section of a biaxial crystal is:
A. "
B. $
C. (
D. 8
4
D
11. The section through a biaxial indicatrix labeled OAP:
A. Is the optic axial plane
B. Shows the maximum possible birefringence
C. Contains the optical axes X and Z
D. All of the above
4
9
A
12. What is the minimum birefringence possible in a biaxial mineral.
A. 0
B. (' - $
C. (' - "
D. ( - "
4
D
13. If a sample is in continuous extinction:
A. It is isometric
B. It is viewed along an optic axis
C. It is isotropic
D. Any of the above
9
D
14. The X-ray line labeled L$ is a transition between which levels?
A. n = 2 to n = 1
B. n = 3 to n = 1
C. n = 4 to n = 1
D. n = 4 to n = 2
7
A
15. In order to filter K$ an iron X-ray tube, which element should be used as a filter?
A. Mn
B. Co
C. Ni
D. Cu
9
A
16. The condition for successful reinforcement of X-ray waves reflected off different
layers in a crystal structure is given by which equation?
A. Bragg
B. Brewster
C. Cauchy
D. Snell
2
D
17. Extinction which looks like a wave passing across a crystal as the stage is rotated is
said to be:
A. Inclined
B. Parallel
C. Symmetric
D. Undulatory
3
C
18. Which of the following phases is a high pressure phase of silica?
A. Cristabolite
B. Quartz
C. Stishovite
D. Tridymite
5
8
B
19. In the expression, I/I0 = e-kt, what does “t” refer to?
A. Temperature
B. Thickness
C. Time
D. None of the above
7
A
20. Minerals from which of the following systems would be uniaxial?
A. Hexagonal - the only one with a high-order axis
B. Monoclinic
C. Orthorhombic
D. Triclinic
6
D
21. Parallel or straight extinction is not possible in what type of crystals?
A. Hexagonal
B. Monoclinic
C. Orthorhombic
D. Triclinic
4
B
22. One nanometer is equivalent to how many centimeters?
A. 10-9
B. 10-7
C. 107
D. 109
5
A
23. The bonding within the graphene layers in graphite is due to what type of bonds? Read
question carefully - Within the layer, not between layers
A. Covalent
B. Ionic
C. Van der Waals
D. Metallic
3
A
24. When minerals with metallic luster weather they may appear to have which of the
following lusters?
A. Dull
B. Glistening
C. Semi-metallic
D. Waxy
3
C
25. Moving electrical currents generate magnetic forces. What is the source(s) of
magnetic force in a transition metal ion?
A. Electrons orbiting the nucleus
B. Electrons spinning around their own axes
C. Both A and B
D. None of the above
6
3
D
26. The symbol {121} represents:
A. Point
B. Line
C. Plane
D. Form
3
A
27. Which of the following forms of radiation is the most energetic?
A. Gamma
B. Infra-red
C. Ultraviolet
D. Visible
3
A
28. Which quantum number determines the shape of the electronic orbital?
A. Azimuthal quantum number, R (see text, page 40)
B. Magnetic quantum number, m
C. Principal quantum number, n
D. Spin quantum number, s
Fill-Ins - Write in the word or words which best completes each statement or answers each
question. (1 point per blank)
3
1. An INTENSIVE PROPERTY
does not depend on the amount of material
present. Examples of such properties include density and temperature.
3
2. The ratio of the speed of light in vacuum to the speed of light in a medium, such as a mineral, is
the INDEX OF REFRACTION .
1
3. Many colored anisotropic minerals, viewed in plane polarized light, will show a change in
color as the stage is rotated. This phenomenon is known as PLEOCHROISM
3,5
4-5 2Vx is 34°. What is the optical class? 4) BIAXIAL
.
What is the optical sign?
5) NEGATIVE
7
6. When light passes from a medium of low index of refraction to one of higher refractive index,
the light will be refracted
TOWARD
the normal.
7
7. How many significant figures are expressed in the number 0.00470 (± 0.00002)? THREE
7
8. Elements whose valance electrons may be denoted as ns2 are called
ALKALINE EARTHS
8
.
9. Luster observed on cleavage faces that are parallel to perfect cleavage planes is often
PEARLY
.
7
10-11 Viktor Goldschmidt described two rules, really empirical observations, governing ionic
substitution. What are these rules?
8.5
10) CHARGE ON THE IONS CANNOT DIFFER BY MORE THAN ONE
7
11) FREE SUBSTITUTION OCCURS IF SIZE DIFFERS BY LESS THAN 15%, AND
LIMITED SUBSTITUTION OCCURS IF SIZE DIFFERENCES BETWEEN IONS ARE
BETWEEN 15 AND 30%
Diagrams and Figures - A series of slides will be shown. Each of these is a photo or a diagram
previously seen in class. Diagrams may have been altered to remove labels, etc. Answer each
question as the slide is shown. (1 point each)
3
C
1. The diagram shown here is a:
A. Binary solid solution diagram
B. Binary congruent melting diagram
C. Binary incongruent melting diagram
D. Binary minimum melting diagram
2
A
2. Point 12 on this diagram has what composition?
A. 30 % Limestone, 60 % sandstone, 10 % shale
B. 60 % Limestone, 10 % sandstone, 30 % shale
C. 10 % Limestone, 30 % sandstone, 60 % shale
D. 10 % Limestone, 60 % sandstone, 30 % shale
4
D
3. The diagram shown here is a:
A. Binary solid solution diagram
B. Binary congruent melting diagram
C. Binary incongruent melting diagram
D. Binary minimum melting diagram
6
F
4. (T-F) The figure shown is the indicatrix for a biaxial crystal.
4
A
5. The plane shown in pink is:
A. Circular section
B. Elliptical section
C. Principal section
D. Random section
0
T
6. (T-F) The diagram shown pertains to an anisotropic crystal.
8
4
13
D
7. What is the optical class and sign of the mineral represented by the section shown?
A. Uniaxial positive
B. Uniaxial negative
C. Biaxial positive
D. Biaxial negative
8. What name is given to the section shown?
IT IS THE OPTICAL AXIAL PLANE (OAP) SECTION
9-13 pertain to figure 1:
Figure 1 - Phase diagram for water
2
What are the following regions?
9. Region A Solid (Ice)
3
10. Region B
Liquid
5
11. Region C
Vapor
What are the following points?
8
12. Point D
Triple point
10
13. Point E
Critical point
9
Matching - Match the discovery in column one with the person associated with the discovery in
column two. Answers may be used once, more than one, or not at all (One point each)
Column 1
0
2
3
9
0
Column 2
K 1. A mathematical formula, which
relates the angle of incidence to the angle of
refraction, was discovered by several
people, one of whom was a Dutch
mathematician, for whom it was named.
A. Roy G. Biv
I 2. One of the greatest American
scientists of the 19th century, he was
awarded the first Doctor of Engineering in
the U.S., and was appointed Professor of
Mathematical Physics at Yale in 1871. His
name is now attached with rule that is of
great importance in geochemistry,
mineralogy, and petrology, as well as many
areas outside of the geosciences.
D. Sir David Brewster
D 3. The condition for maximum
polarization of reflected and refracted rays is
named for this Scottish physicist.
I. Josiah Willard Gibbs
L 4. German physicist who won the Nobel
Prize in Physics in 1914 for the discovery of
diffraction of X-rays by crystals
K. Willebrod Snellius
E 5. An American Crystallographer who
developed the precession camera.
M. Karl Weissenburg
B. Sir William Henry Bragg
C. Sir William Lawrence Bragg
E. Martin J. Buerger
F. Albert Einstein
G. Sir Lazarus Fletcher
H. Joseph von Fraunhofer
J. Wilhelm C. Roentgen
L. Max Theodore Felix von Laue
10
Problems - Do each of the following problems. Show all work. Label answers, including
units, if any. List any formula used, and define all symbols used in the formula. “Miraculous
answers”, unsupported by all necessary calculations, will receive little or no credit.
10
1. 1. Dolomite belongs to the hexagonal crystal system, with , = 1.500 and T = 1.681.
What is the optical class and sign of dolomite? (2 points)
19.5
Uniaxial negative
2. What is the retardation, expressed in nm, of a crystal of dolomite of standard thickness, which
shows the maximum possible birefringence? (2 points)
•  = t(N – n)      mm (1681
.
 1500
. )  0.030 (0181
. ) 
5.40 x 10  3 mm  5400 nm
16
3. Given: cvacuum = 2.998 x 108 m/s
If f = 5.66 x 1014 Hz, what is 8 (expressed in nm)? (3 points)
11
21
4. Hercynite has the formula FeAl2O4, and has n = 1.80. If light passes from hercynite into air,
what is the critical angle? (3 points)
16.5
5. Assuming a standard thin section thickness of 30 microns, what is the retardation value for
cassiterite (tetragonal, T = 1.997, , = 2.093)? Express your answer in nanometers. (2 points)
() = (2.093 - 1.997) x 0.03 mm x 106 nm/mm) = 2880 nm
)=
2900 nm
12
Figure 2
Answer each of the following questions which pertain to figure 2. (1 point each)
0
6. Show all liquidus lines in green.
9
7. Show all solidus lines in yellow.
4.5
8. Starting at point A in the diagram, trace the path followed by the liquid in red as the system cools to 900°C.
9.5
9. Trace the path followed by the solid(s) from the point of first crystallization to 900°C in blue.
3
10. What is point B called?
PERITECTIC
0
11. What is point C called?
EUTECTIC
7.5
12. At what temperature does solid X disappear?
6.5
13. What is the composition of the liquid at 1100°C?
9
14. What is the percent liquid at 1100°C? 16%
11
15. What is the percent solid at 1100°C? 84%
1190°C
38% Z
13
Discussion questions - Write a complete, concise answer to each of the following questions.
Diagrams (labeled) may be used to supplement your written answers, where appropriate. Points as
shown
1. Make a labeled sketch of an X-ray tube showing the following features:(5 points)
7 A. Focusing shield
4 D. Water conduit
6 B. Target
3 E. Path followed by electron stream
6 C. X-ray ports
14
22
2. Describe how X-rays are produced in an X-ray tube. Why is it necessary to cool an X-ray tube
with water? (3 points)
X-RAYS ARE PRODUCED BY BOMBARDING A METAL TARGET WITH
ELECTRONS BOILED OFF AN ELECTRODE AN ACCELERATED THROUGH
VACUUM BY A LARGE VOLTAGE DIFFERENCE. THE ELECTRONS HIT THE
TARGET WITH VERY HIGH KINETIC ENERGY, KNOCKING OUT THE INNER
ELECTRONS ON THE TARGET NUCLEI, WHICH THEN EMIT X-RAYS AS
ELECTRONS DROP INTO VACANT INNER ORBITAL POSITIONS. THE KINETIC
ENERGY OF THE ELECTRONS MAKES THE TARGET VERY HOT, AND WOULD
SOON VAPORIZE IT IF IT WERE NOT COOLED
18
3. Both calcite and quartz occur as transparent uniaxial crystals, but only calcite is capable of
showing double refraction in a crystal whose dimensions are 2-3 centimeters. Why? (3 points)
THE DIVERGENCE OF THE ORDINARY AND EXTRAORDINARY RAYS IN A
CRYSTAL PRODUCE DOUBLE REFRACTION. WHEN THE BIREFRINGENCE IS
SMALL, THE ANGLE BETWEEN THE TWO RAYS IS VERY SMALL, AND ONLY
ONE IMAGE IS SEEN. THIS IS THE CASE FOR QUARTZ. IN HIGHLY
BIREFRINGENT MINERALS, LIKE CALCITE, THE RAYS QUICKLY SPREAD
APART, AND TWO IMAGES ARE SEEN.
HAVE A GREAT VACATION AND
A VERY HAPPY AND SAFE NEW YEAR!
15
Final Examination Grades
107.0
106.0
105.5
A+
100.0
98.5
A-
96.0
B+
89.0
B-
83.5
C+
MEDIAN = 82.8
82.0
C
MEAN = 82.2 (76.1%, C)
72.0 - 2
71.0
68.0
D
59.0
55.5
49.5
F
16
Previous Years Results -Final Examination
Term, Year
Mean, %
Fall, 2011
76.1
Fall, 2010
70.0
Fall, 2009
68.8
Spring, 2009
75.6
Fall, 2007
73.9
Fall, 2006
73.7
Fall, 2005
69.0
Spring, 2004
89.7
Fall, 2002
73.2
Spring, 2001
69.7
Spring, 2000
87.2
Fall, 1998
66.8
Fall, 1997
76.8
Fall, 1996
71.5
Fall, 1995
76.1
Fall, 1994
69.6
Fall, 1993
79.6
Fall, 1992
73.2
Fall, 1991
73.8
Tied for fourth of out 19
17
TOTAL EXAMINATION RESULTS
(OUT OF 288; 48% OF FINAL GRADE)
271.5
A
263.0
260.5
A-
257.0
254.5
B+
248.0
B
226.0
C+
219.0
217.5
MEAN = 219.3 (76.1%)
C
MEDIAN = 218.3
208.0
206.5
C-
193.5
193.0
D+
174.5
D-
170.0
145.5
F
In 2010, the highest grade on the exams was 247.5, so part of this group did well.
However, the 2010 Mean was also 219.3, so some students did not do as well.
DO PREREQUISITES MATTER?
Judge for yourself
Students missing some or all prerequisites - average = 71.7% (C-)
Students with proper prerequisites - average = 89.4 % (B+)
18