Faculty of Science
Geology Department
Second level geology 2012-2013
First semester exam.
Optical mineralogy (GE201)
Question NO.1
1- Choose the correct answer (20 degrees)
1- The color violet occurs at what position in the electromagnetic spectrum?
a .above red colour
b- below yellow color
c-between green and blue
2- The quantitative expression of double refraction is:
a. Retardation
b Birefraction
c. Direfraction
4. Birefringence
3- The magnifications available on typical student microscopes are:
1. 40, 100,400
2.40,400,1000
3.4,40,
4.2.5,10,40
4- A retardation of 550 nm would yield an interference color of:
1. yellow (green)
2. green
3. gray
4. red (purple)
5- Working distance in microscopy refers to:
1. Distance between eye and ocular.
2. Distance between ocular and objective.
3. Distance between condenser and specimen.
4. Distance between objective and specimen.
6- Wave theory effectively describes the phenomenaof:
a- polarization
b- reflection,
c- refraction and interference
7-Retardaton
(delta -A)is measpred by:
a-millimeters
b- nanometers
\
c-cintemeters
8-If retardation
\
,.
~
,
\
is a/whole number (i.e., 0,1,2,3,
I
\
etc.) of wavelengths The two wa~s, A and B,
I
are IN PHASE:
a- they constructively
interfere with each other.The resultant wave (R) is the sum of A and B.
b- they destructively interfere; cancelling each other out, producing the resultant wave (R), which has
no amplitude or wavelength.
c- the interference being partially constructiveand partialy destructive
9- In calcite the refractive index for the ordinary ray is.... and for extraordinary
ray is.... :
a- 1.52 and 1.69 respectively.
b- 1.66 and 1.89 respectively.
c- 1.66 and 1.49 respectively ..
d- 1.72 and 1.98 respectively.
10- A high Refractive Index indicates:
a-a low velocity of light at a particular medium.
b-a high velocity of light
c-high light polarization.
11- Snell,s law relates:
a-retardation and phase difference
b-birefrengence
and thickness of mineral plate
c-index of refraction and velocity of light
12-Which of the following minerals is noted for its one perfect cleavage?
a- calcite
b-) muscovite
c- quartz
d- pyrite
13-Which of the following minerals almost has twinning:
a-quartz
b-olivine
c-plagioclase
14- prism method is used for:
a-mesurernment of refractive index of minerals
b-production of convergent light
c-production of polarized light
15- It takes ------- indices of refraction to describe optical properties of biaxial minerals
16- Ordinary
- extraordinary
rays terminology
is not used for biaxial minerals because:
a-both rays behave as ordinary ray
b-both rays are slow rays
\
c-both rays behave as the extraordinary ray
,
17- The single optic axis in uniaxial minerals is cMncident ;itb
I
a-the c- axis in monoclinic and triclinic minerals
b- the c-crystallographic
axis in tetragonal and hexagonal minerals.
c-the b-axis in trigonal minerals.'
18- in ray velocity surface of doubly refracted
rays tbe mineral is positive when:
a- the sphere is inside the ellips
b-the ellips is inside the sphere
c-non of both
19- the Becke Line always moving into the material witb:
a- the higher refractive index
b-the lower refractive index
c-the same refractive index
20-which of tbe following minerals bas parallel extinction:
a-olivine
b-biotite
c-homblende
Question No.n
Mark with ( ~ ) or (X
) and rewrite the wrong following sentences
(30
degrees)
I) The depressive power of a glass prism is determined by the difference between the angle of
deviation of yellow and violet color
(
)
2) Hexagonal minerals should have isotropic optical properties. (
)
3) Dispersion would account for the birefringence seen in diamonds. ( )
4) Twinkling would account for the change in color of biotite when the microscope stage is rotated.
5) The ocular lenses are rotated in and out to change magnification.(
)
6) Pleochroism would account for the change in color of plagioclase when the microscope stage is
rotated.
(
)
7) In monoclinic minerals the optic axis is not a crystallographic axis. (
8) Calcite has a +ve uniaxial indicatrix.
9) Ultraviolet
(
)
)
radiation has longer wave length than the infrared radiation.
(
)
10) Standing at the edge of a swimming pool, objects seen at the bottom appear to be deeper than they
actually are. (
)
II) Interference of two waves with ~ Apath difference gives maximum intensity
interference colors.
(
)
12) White light is composed of seven frequencies.
(
)
13) The vibration directi~n of ordinary ray in quartz is parallel to the direction of
the plane containing the a-and b crystallographic axes.
(
)
14) Amplitude is the minimum displacement from the line of transmission of
\
light. ()
I
\
15) High re~f of minerals means high refractive index.
f
()
I
I
16) Flash interference figures are characteristic only to uniaxial minerals in sections parallel to the
optic axis.
(
)
17) Wave surface of uniaxial minerals is sphere.
(
).
18) When double refraction occurred in calcite the ordinary ray will be parallel to the long diagonal and
the extraordinary ray will be parallel to the short diagonal of rhombic face of the cleavage
rhombohedra.
()
19) The split of light into respective seven colors of spectrum is called refraction
20) The indicatrix of orthoclase (monoclinic) is uniaxial.
(
(
)
21) The 2v angle is the obtuse angle between the optic axes of the biaxial
indicatrix.
(
)
22-When the retardation is a whole multiple of wavelengths (n A. ) no interference
23-Augite has two sets of cleavages with 56 or 124 apart.
0
0
(
(
)
)
24- If the acute bisectrix is Z crystallographic axis the mineral is optically -ve.
25- In tetragonal minerals the optic axis is not a crystallographic axis.
26- Hornblende has parallel extinction
occurs.
(
(
)
)
()
27- Pleochroic colors can be best studied between crossed Nicoles
(
)
28- The vibration direction of ordinary ray in quartz is parallel to the direction of the plane containing
the a-and b crystallographic
axes.
(
)
29- Calcite has a +ve optic sign because the fast ray vibrating in a direction parralel to the optic axis.
30- An elongated crystal is said to have positive elongation if the slow ray is in the direction of the
longer axis
(
)
Question NO.III
Rewrite or complete the following sentences.'
1-
(25 degrees)
On determining the refractive index of mineral plate by glass hemisphere, the refractive index
equation is
.
2-
The split of light into respective seven colors of spectrum is called
3-
Augite has
4-
The indicatrix of orthoclase (monoclinic) is
5-
The relation between retardation and phase difference is
6-
When two· monochromatic
7-
When retardation is equal to whole multiple of A ---------------are produced.
8-
----------light has the maximum wavelength in the visible light.
.
extinction.
.
.
waves are equal and opposite in phase -----------intensity of light will
9-
----------- is the maximum displacement from the Ijine of transmission of light.
10- 2V angle is
.
11- Speed of light is equal to ----------------\
12- High relief of minerals means -------------refracfive
index.
13- Wave surface of ---------------- minerJCs is sPhere~
I
14- The formula of Snell,s law is
.
15- Changes in absorption color in PPL as rotate microscope stage is called-----------------.
16- The electromagnetic radiation theory of light implies that light consists of ------------and ---------components which vibrate at right angles to the direction of propagation.
17- -----------materia1s show the same velocity oflight in all directions while------- minerals have a
different velocity for light, depending on the direction the light is travelling through the mineral.
18- The relationship (02 - nl) is called -----------------19- Monochromatic light has ------------ wavelength while white light has --------wavelengths.
20- The dispersive power of a prism is determined by the difference between the---------------------and
21- Critical angle is ---------------------------22- Double refraction is----------------------23- Wave surface of doubly refracted rays is represented by--------------------24- If the velocity of light is maximum, the refractive index will be-------25-
When the extraordinary ray is the fast ray the mineral has --------------sign.
Question NO.IV (15 degrees)
If you have a mineral has refractive index n= 1.486 in the direction of c-axis and
n= 1.658 in the direction normal to the c- axis, answer the followings:
1-What is the type of this mineral and the possible crystal systems such minerals usually belong to.
Examination commetee
~~
Dr. Samia Kamal Ibrahim.
A"
Prof. Dr. Mostafa Hassanein Hshad J1~?j.......S'-Dr.Ibrahim Hussein Khalifa
:I..\~
-