Download Midterm 1 Key - Florida Atlantic University

GLY4310
Name
60 points
February 2, 2017
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
PETROLOGY -- MIDTERM ONE 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)
1
T
1. The geothermal gradient in the earth's crust is much more variable than the
geobarometric gradient.
7
F
2. Seismic discontinuities in the earth's interior at depths of 410 and 660 km below the
surface are believed to be due to changes in composition of the earth between layers.
1
F
3. Primary minerals in igneous rocks form by alteration of the rock after crystallization.
1
T
4. During nucleation, the surface area/volume ratio is extremely high.
8
F
5. A crystal completely bounded by its own natural crystal faces is said to be
idiomorphic.
0
F
6. Petrology is the branch of geology dealing with the description and systematic
classification of rocks, especially igneous and metamorphic rocks, and especially by
means of microscopic examination of rock thin sections.
2
F
7. The alkali feldspars form a complete solid-solution series at room-temperature.
5
T
8. Octahedral layers hold t-o-t units together in tetraphormic phyllosilicates.
2
T
9. Phyllosilicate minerals are often formed by rock weathering and are important
constituents of soil.
0
F
10. A melanocratic rock is light in color.
1
F
11. In biotite-hornblende granite, biotite and hornblende are accessory minerals, and there
is more biotite than hornblende present.
4
T
12. Undulatory extinction results from post-solidification deformation.
1
Multiple-Choice - Choose the best response to each statement or question. Print the letter
corresponding to your choice in the blank. (1 point each)
6
C
1. Pyroxenes which contain relatively large cations (Ca2+, Na+) belong to which crystal
system?
A. Hexagonal
B. Orthorhombic
C. Monoclinic
D. Triclinic
2
B
2. Which of the following groups of minerals is hydrous?
A. Olivine
B. Amphibole
C. Pyroxene
D. Garnet
2
B
3. The charge on the (SiO4) group is:
A. -2
B. -4
C. 0
D. +4
4
D
4. Sanidine is a type of:
A. Pyroxene
B. Plagioclase feldspar
C. Silica
D. Potassium feldspar
2
C
5. Albite and anorthite form a solid solution series. The cations involved in the solid
solution are:
A. Potassium, sodium, aluminum, and silicon
B. Lithium, boron, silicon, and titanium
C. Sodium, calcium, aluminum, and silicon
D. Sodium, calcium, aluminum, and titanium
0
B
6. Which of the following minerals is an orthoamphibole?
A. Actinolite
B. Anthophyllite
C. Grunerite
D. Riebeckite
2
1
D
7. In the IUGS classification of igneous rocks, which of the following can be used to
modify a rock name?
A. Mineralogical term
B. Textural term
C. Chemical term
D. Any combination of the above
0
A
8. Rocks composed primarily of silica-rich minerals, generally feldspars and silica,
whose common minerals include plagioclase feldspar, alkali feldspar, quartz, and
muscovite, the term can be used to modify either a mineral or a rock name. This is this a
description of which of the following terms?
A. Felsic
B. Fragmental
C. Mafic
D. Porphyritic
1
C
9. Expansion and contraction of some members of this mineral group can cause
structural damage. Which group is this?
A. Alkali feldspars
B. Chlorites
C. Clays
D. Zeolites
9
C
10. Which of the following minerals contains the most calcium? All Old Andean Ladies
Buy Anchovies - now which end is the Ca-rich end?
A. Albite
B. Andesine
C. Bytownite
D. Oligoclase
0
D
11. Which of the following minerals is a member of the Al2SiO5 group, important
pressure-temperature indicators in some metamorphic rocks?
A. Andalusite
B. Kyanite
C. Sillimanite
D. All of the above
6
A
12.
is the reaction of calcic plagioclase to form nearly pure
albite plus an epidote mineral.
A. Saussuritization
B. Seritization
C. Serpentinization
D. Uralization
3
0
B
13. A rock is composed of predominantly subhedral crystals. The rock texture may be
described as:
A. Equant
B. Hypidomorphic
C. Idiomorphic
D. Xenomorphic
0
A
14. The most common metal on earth is:
A. Aluminum
B. Calcium
C. Iron
D. Titanium
2
C
15. A rock with 45% dark minerals would have which color classification?
A. Leucocratic
B. Melanocratic
C. Mesotype
D. Poikilitic
3
B
16. Large crystals formed by relatively slow cooling of magma below the earth’s surface
are called:
A. Phaneritic
B. Phenocrysts
C. Pyroclasts
D. Xenocrysts
1
B
17. The mica minerals contain the K+ ion in XII coordinated cages. The bonding is weak
and the cages are easily distorted, which contributes to the elasticity of the micas. In
brittle micas, what ion replaces the K+ ion?
A. Na+
B. Ca2+
C. Al3+
D. Fe2+
1
D
18. The most important rock-forming mineral in the sorosilicate sub-class is:
A. Hemimorphite
B. Vesuvianite
C. Sphene
D. Epidote
4
7
B
19. A rock containing 2.85% Na2O, 0.92% K2O, 9.70% CaO, and 17.41% Al2O3 will
fall into which category on the alumina saturation classification?
A. Peralkaline
B. Peraluminous
C. Metaluminous
D. Subaluminous
5
B
20. A texture in which a K-spar oikocryst contains inclusions of other minerals, which it
completely surrounds, is called:
A. Ophitic
B. Poikilitic
C. Spinfex
D. Trachytoid
Fill-Ins - Write in the word or words which best completes each statement or answers each
question. (1 point per blank)
4
1. In a trioctahedral phyllosilicate the cations will be DIVALENT
(oxidation state of
the cations).
4
2. A type of intergrowth in which K-spar is the host and albite is a coherent intergrowth is known
as
3
PERTHITE
.
3. Minerals, like biotite or hornblende in granite, which may be present but are not required are
known as ACCESSORY
minerals.
3
4. The most abundant element in the earth is OXYGEN
4
5. The second most abundant element in the earth is
SILICON
.
.
6-7. Name and describe two factors that are important in determining whether a crystal is
euhedral or anhedral?
7.5
6). CRYSTALS WHICH FORM VERY EARLY IN THE CRYSTALLIZATION PROCESS
ARE OFTEN EUHEDRAL, BECAUSE THEY ARE GROWING INTO LIQUID, WHICH
OFFERS LITTLE RESISTANCE TO GROWTH.
10.5
7). FORCE OF CRYSTALLIZATION - THE SURFACE ENERGY OF SOME MINERALS IS
MUCH LOWER THAN OTHERS. MINERALS WITH LOW SURFACE ENERGY WILL
USUALLY BE EUHEDRAL. THE METAMORPHIC MINERALS GARNET AND
STAUROLITE, AND THE IGNEOUS MINERALS ZIRCON, APATITE, AND TITANITE
ARE EXAMPLES.
5
8-9. The transition from the mantle to the outer core occurs about 2900 kilometers below the
surface. There are two forms of evidence, both based on seismic waves, that indicate the outer
core is a liquid. Briefly describe each.
0.5
8) COMPRESSIONAL SEISMIC WAVES SLOW DOWN DRAMATICALLY AT THE
MANTLE -CORE BOUNDARY.
1.5
9) SHEAR SEISMIC WAVES DO NOT PASS THROUGH THE OUTER CORE.
1
10. Give the correct symbol for the layer structure in a triphormic phyllosilicate.
T-O-T
Matching I - Match the description in column one with the correct silicate subclass in column 2.
(1 point each) Answers may be used once, more than once, or not at all.
Column 1
1
A 1. Tourmaline and beryl are two of the
more common minerals of this sub-class.
0
F 2. The most common minerals in the
earth’s crust belong to this subclass.
8
C 3. This sub-class has the lowest Si:O
ratio.
1
E 4. The Si2O7 structure characterizes this
sub-class.
12
C 5. Members of the Al2SiO5 polymorphs
all have a chain of Al octahedra formed by
edge sharing. They belong to which subclass? Inosilicates have chains of tetrahedra
5
C 6. Olivine, a major constituent of the
earth’s mantle and perhaps the most
common mineral on earth, belongs to this
subclass.
Column 2
A. Cyclosilicate
B. Inosilicate
C. Nesosilicate
D. Phyllosilicate
E. Sorosilicate
F. Tectosilicate
6
Matching II -Match the descriptions from column 1 with the correct silicate group from column
2. Answers may be used once, more than once, or not at all. (1 point each)
Column 1
Column 2
2
G 1. Members of this group, including
leucite, sodalite, and nepheline, are never
found in igneous rocks with quartz.
3
B 2. Microcline, orthoclase, and sanidine,
members of this group, are commonly found
in rocks near the left apex of the IUGS
diagram.
2
O 3. Tridymite, cristobalite, coesite, and
stishovite all belong to this group.
6
L 4. Enstatite, diopside, augite, and
aegirine belong to this group.
0
H 5. Members of this group are often
split into those with calcium, and those
without. The grains are usually euhedral, and
are isometric. Examples include uvarovite,
almandine, andradite, and grossularite.
A. Al2SiO5
B.. Alkali feldspar
C. Amphibole
D. Chlorite
E. Clay
F. Epidote
G. Feldspathoid
H. Garnet
I. Mica
J. Olivine
K. Plagioclase feldspar
L. Pyroxene
M. Pyroxenoid
N. Serpentine
O. Silica
P. Zeolite
6
K 6. The name of this important mineral
group comes from words meaning “oblique”
and “break”, in allusion to their triclinic
structure.
3
L 7. The minerals at the bottom of a foursided structure used to describe the chemistry
of this group are enstatite and orthoferrosilite.
Along the upper edge we fine diopside and
hedenbergite.
2
C 8. Minerals in this group are often
elongated prisms, and possess 60 cleavage.
Examples include riebeckite, hornblende,
anthophyllite, and glaucophane.
7
Short Answer - Write a complete, concise answer to TWO of the following three questions.
Diagrams (labeled) may be used to supplement your written answers, where appropriate. 4 points
each
.
1. Use the diagram in Figure 1 to explain how an
intrusive porphyry might form
Figure 1
DIFFERENT MINERALS IN THE SAME MELT EXHIBIT BEHAVIOR AS SHOWN IN THE
DIAGRAM, BUT A DIFFERENT TEMPERATURES. AT ANY GIVEN TEMPERATURE, ONE
MINERAL MIGHT BE AT A POSITION SIMILAR TO THAT LABELED Ta IN THE
DIAGRAM. SUCH A MINERAL WILL NUCLEATE FEW GRAINS, BUT THESE WILL
GROW LARGE. FOR A SECOND MINERAL, THE SAME PHYSICAL TEMPERATURE
WILL CORRESPOND TO A POSITION SUCH AS THAT LABELED Tb IN THE DIAGRAM..
THIS MINERAL WILL NUCLEATE MANY GRAINS, BUT THEY WILL ALL BE SMALL.
SUCH A ROCK, WITH LARGE GRAINS EMBEDDED IN MANY SMALLER GRAINS,
RESEMBLES A PORPHYRITIC TEXTURE IN EXTRUSIVE IGNEOUS ROCKS.
8
2. Explain what a deuteric autometamorphic process is. Name and describe what is happening in
two examples of a deuteric process.
AS INTRUSIVE IGNEOUS ROCKS COOL SLOWLY, THEY WILL PASS THROUGH A
RANGE OF TEMPERATURES USUALLY ASSOCIATED WITH METAMORPHOSIS,
ROUGHLY 300-800C. THE MINERALS IN THE ROCK MAY BE ALTERED. IF THE
REACTIONS INVOLVE WATER, THEY ARE TERMED DEUTERIC. EXAMPLES:
1)URALIZATION, IN WHICH PYROXENE IS CONVERTED TO AMPHIBOLE
2) BIOTITIZATION, IN WHICH EITHER PYROXENE OR AMPHIBOLE IS
CONVERTED TO BIOTITE
3) CHLORITIZATION IN WHICH A MAFIC MINERAL IS CONVERTED TO
CHLORITE
4) SERITIZATION IF THE CONVERSION OF FELSIC MINERALS TO VERY FINEGRAINED WHITE MICA
5) SAUSSURIZATION IS THE REACTION OF CALCIC PLAGIOCLASE TO FROM
NEARLY PURE ALBITE PLUS EPIDOTE
6) SERPENTINIZATION IS THE BREAKDOWN OF ANHYDROUS MAFIC
MINERALS TO FORM SERPENTINE MINERALS
Question #
Times Answered
Points Missed
Average
1
12
15.5
1.3
2
5
5
1.0
3
17
13
0.8
9
3. What formula is used to determine the variation of pressure
with depth within the earth? (List the formula, and define all
terms in the formula) Examine Figure 2. It is clear that
pressure is nearly a linear function of depth within the mantle,
but deviates considerably in the core. Explain this behavior,
using the above formula.
Figure 2
THE FORMULA IS:
P = ρgh, where
P = pressure
ρ = density
g = acceleration due to gravity
h = the height of the column of material above the object
WITHIN THE MANTLE DENSITY AND THE HEIGHT OF THE COLUMN INCREASE AS
DEPTH INCREASES, WHILE G DECREASES, ALL IN LINEAR MANNERS. AT THE TOP
OF THE OUTER CORE, DENSITY INCREASES RAPIDLY AND NON-LINEARLY, AS
SILICATES ARE REPLACED BY IRON-NICKEL.
10
Midterm 1 Results
61.5
60.0
58.0 - 2
55.0 - 2
53.0
52.0
50.5
50.0 - 2
47.5
45.0
43.0 - 2
37.0
A+
A
AB+
MEDIAN = 51.3
MEAN = 51.2 (85.3%)
B
C+
C
CD-
Previous Results
2017 - 85.3%
2016 - 78.9%
2015 - 69.5%
2014 - 75.8%
2013 - 77.1%
2012 - 81.3%
2011 - 77.5%
2010 - 76.2%
2009 - 70.4%
2008 - 81.9%
2006 - 78.6%
2001 - 73.3%
1999 - 76.0%
1998 - 81.6%
1997 - 79.8%
1996 - 84.3%
1995 - 82.0%
1994 - 76.1%
1993 - 87.1%
1992 - 87.3%
1991 - 80.0%
Third out of twenty-one
11