Name:___________________________________________
Geos 306
2 2011 Midterm (100 pts)
nd
1) (10 pts) Fill in the table that defines the shape and constraints of the unit cell
parameters.
System
Cubic
a
b
c
Hexagonal
Tetragonal
Orthorhombic
Monoclinic
Triclinic
1
α
β
γ
2) (20 pts) Draw a picture of an orthorhombic lattice projected onto the b-c plane
(i.e. you do not need to show the a-direction); indicate the origin and the cell
edges.
a) Draw and label the vector [0 1 2].
b) Draw and label the plane (0 1 2).
Assume a = 4 Å, b = 3 Å, c = 5 Å.
c) Calculated the length of the [0 1 2] vector.
d) Calculate the d-spacing of the (0 1 2) plane using geometry.
e) Using Bragg’s equation with Cu radiation, λ = 1.54 Å, what position in 2θ
would the (0 1 2) peak be found.
2
3) (30 pts) Fill in the missing point group symbols and indicate the crystal system for
the point groups on a given row.
G
GUGi
HUG\Hi
System
n/a
triclinic
m
3
n/a
4/m
6mm
222
3mm
4/m2/m2/m
622
332
n/a
cubic
3
4) (15 pts) From the microprobe analyses of a solid-solution mineral, the following
oxide weight percents were measured. Determine the chemical composition of
this sample.
Weight percent
MgO
52.445
SiO2
41.587
FeO
5.967
Bonus: Name the solid-solution pair of minerals (5 points) (eg diopside-jadeite),
or name the mineral (2 points), or name the mineral group (1 point).
4
5) (5 pts) Write down the number of your model and define its point group
symmetry.
5
6) (10 pts) One of the diffraction patterns below was recorded on a cubic mineral;
the other is from a triclinic mineral. Identify which pattern is from the cubic
mineral and give a reason for your choice. For a hint, think about the positions of
the (100), (010) and (001) peaks.
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7) (10 pts) Below is a Raman spectrum of topaz, Al2SiO4F2.
a. Describe the origin of Raman peaks.
b. What is the strongest bond in topaz?
c. Indicate the position of the peak on the Raman spectrum that corresponds
to the strongest bond.
7