The document describes the parts and working of a polarizing microscope. It has optical components like polarizers, analyzers and lenses, and mechanical components like the rotating stage. Light from the specimen is polarized and its interaction with the optical components is used to identify properties of minerals and rocks. The polarized microscope allows examination of anisotropic materials and determination of their optical characteristics, which has applications in geology and mineral exploration.

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Polarizing Microscope
DEPARTMENT OF GEOLOGY
Guided By :- Presented By :-
Dr. Narendra Joshi Amit Rathore
Class- M.Sc. ( I Sem)

2. CONTENT:-
1. INTRODUCTION
2. PARTS OF POLARISING MICROSCOPE
3. WORKING OF POLARISING MICROSCOPE
4. SIGNIFICANCE
5. CONCLUSION
6. REFRENCE
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3.  INTRODUCTION:-
Polarizing Microscope( Petrological microscope): In
the year (1768-1851), William Nicol discovered
polarizing Microscope. It is used in the study mainly
for the identification of optical properties of the given
specimen ( i.e. rock ) which is in the form of thin
sections of the rocks and minerals. It is a typical
transmitted-light microscope.
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Fig no 1 Monocular polarized Microscope

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Microscope:-
A microscope is an instrument which is used to study the
micro or too small objects which is not sufficient to see clear
objects by our naked eyes. There are many different types of
microscope which is used on the basis of essential field work.
It is majorly three types of microscope:-
a) Simple Microscope
b) Compound Microscope
c) Electron Microscope
But In The field of Geology, we have to study the thin section
of the rock type, the type of modified Compound Microscope
( i.e. Polarizing Microscope) is used.

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Polaroid is an optical filter which is filtered the unpolarised light( i.e. light source of bulb,
natural light, etc.). It is a device which is used to analyze or create polarized light.
Normal light vibrate in many plane or vibration. In polarizing Microscope, a polarizer is used
which allow passage of light of one vibration direction.
 Polaroid:-
Fig No 2
Fig No 3

7. Parts of Polarising Microscope
It is majorly different parts of this Microscope on the basis of
Mechanical and Optical Parts.
Types of Petrological Microscope
Optical Parts Mechanical Parts
 Polarizing Prism
Types of Polarizer prism
 Bertrand lens
The Objective lens
The Condensing lens
 Ocular/ Eyepiece
 Huygens eyepiece
 Reflector
Circular rotating Stage
Sub-stage
 Verniers Scale
 Tube
Objective Holder
Slot of Accessories
 Base
 Fine and Coarse Focus
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8. On the basis of Mechanical Parts
• Rotating Stage:- The thin section of a mineral to be
examined is placed on this stage. The axis of rotation of the
stage coincides with the microscope axis. This is also called as
Graduate stage.
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Fig No. 4 Fig No. 5

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• Sub-stage:- The sub-stage is the ring beneath the revolving stage. It carries the
polarizer and, in some microscope, the condensing system. It is described below in
connection with the condensing system.
Fig No. 6

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• Verniers :- Attached to the sides of the stage of most microscopes, there are certain auxilary
scales called verniers after the inventor, Pierre Vernier (1631). These verniers may longer or a
little shorter than the divisions of the main scale.
Fig No. 7 Fig No. 8
Verniers Scale

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• Objective Holders :- Objective may be attached to the tube in one of four ways. In old
microscopes it is necessary to screw each objective into place as it is needed. Strain can also be
introduced if the lens is mounted too tightly on the frame. Also anti reflection coatings and
refractive properties must be accurately accessed in order to ensure polarization.
Fig No 9

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• Observation Tube :-
The tube is the hollow cylinder to which most of
the optical parts are attached. In most
microscopes it is straight or it is inclined at an
angle to enable the observer to sit at ease and
work .

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• Base:-
This base is specially designed
to balanced and proper stand and its shape
is like Horse -shoe shaped base.

14. • Slot of Accessories :- In old microscopes connecting the
tubes with the objective is a short collar containing a slot for
insertion a Quartz wedge or a gypsum or a mica plate.
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Fig No 10

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• Fine and Course Focus Adjustment :-
The large and small circular adjustments on the
lower portion of the body of the microscope are
used to rack the stage up and down for
changing the focus of the objective lens in use.
This adjustment should be used to focus the
thin section.

16. On the basis of Optical Parts
o Polarising Prism :- Many of the most important
characteristics of crystals are determined by Polarised light.
For obtaining polarised light some form of calcite (Iceland
Spar) prism is used. Recently in less costly Polaroids are used
for obtaining polarised light.
It is basically of two types:-
a. Polariser :-
b. Analyser :-
a) Polariser:- The polariser is fitted below the stage. It
transmits polarised light in the East-West direction.
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17. b) Analyser :- The analyser is placed in the microscope tube above the
stage and is removable. The analyser transmits light vibrating in the
North-South direction. When both the polariser and analyser are in
position, they are said to be crossed. Both positions are in the right
angle ( i.e. perpendicular to each other). While such condition happen
then normally no light will pass through and the viewer will only see
darkness.
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Fig No. 11

18. oHuygens Eyepiece:-
The ocular of a microscope is not
nearly so complicated as objective. In most forms but two
lens are used. This Eyepiece is the one most commonly used
in petrographic microscope. It is achromatic in the sense that
images of different colour appear of the same size.
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Huygens Eyepiece Ramsden Eyepiece
Fig No 12 Fig No.13

19. o Bertrand Lens :- . This is given by mineralogist Emile Bertrand. This
lens is used to observe interference figures. A specialized lens mounted
in an intermediate tube or within the observation tubes, a Bertrand lens
projects an interference pattern formed at the objective rear focal plane
into focus at the microscope image plane. The lens is designed to
enabled easy examination of the objective rear focal plane, to allow
accurate adjustment of the illuminating aperture diaphragm and to
view interference figures.
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Fig No. 14

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o Ocular/ Eyepiece :-This is the lens that you look through at the top
of the microscope. The eyepiece of the microscope carries cross-hairs,
one in the North-South direction and the other in the East-West
direction. These cross-hairs help in locating a particular mineral grain for
detailed examination. They are also useful in aligning cleavage
fragments for making angular measurements.
Fig No. 15

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oCondensing Lens:- The condensing lenses are required
below the stage . They are used with high power objective
and produce converging light rays when required. It is located
with lower analyzer. A polarizer condenser has following 3
characteristics-
1) Built-in rotatable Polarizer.
2) Top lens-out construction, when parallel light illumination
at low magnification is required.
3) Strain-free optical system, like the objectives.
Fig No. 16

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o Iris Diaphragm:-
This diaphragm is located below
the stage. It regulates the intensity of light . This is an
adjustment nearest the light source that allows more or less
light to be transmitted to the stage.
Fig No. 17

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oReflector:-
This is the reflector part of the
microscope which is situated in the bottom of the
instrument. It is made up of Plano-concave mirror.
Fig No. 18

24.  Working of Polarising Microscope:-
Preparation of thin section- A thin section of a
mineral (or a rock) is made by grinding and polishing
on one side of a piece of it. This side is then cemented
to a slip of glass with canada balsam. The mineral chip
is then ground down on the other side with
successively fine grades of carborundum powder.
When a suitable thickness is left ( about 0.0265-
0.035mm) a cover slip is cemented on it.
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25. Pathway of Light
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Fig No . 19 Fig No. 20

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 Behavior of transmission light on the following conditions :-
1) When an specimen is not present in the microscope –
Analyzer is pushed completely in place . Now Polarizer is placed and is rotated until the
field of view become dark.
2) When an specimen is in Anisotropic material –
Light passing through these substances splits into two rays that vibrate in perpendicular
direction, Where transmission of light under crossed polarizer ( light splitting ).
Pleochroism possible.
3) When an specimen is in isotropic material-
No transmission of Light under crossed polarizer. Materials whose refractive index not
depend on the direction that light travels are called Isotropic materials .
Fig No. 21 Fig No 22

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Fig No. 23

28.  Conclusions:-
Microscope dedicated for use with polarized light are very sophisticated
instruments having components specifically designed to minimized
strain and provide sharp, crisp and clear images of birefringent
specimens. For simple qualitative work , a standard microscope can be
converted for polarized light studies. Typically, a small circle of Polaroid
film is introduced into the filter tray or beneath the sub-stage condenser
and a second piece is fitted in a cap above the eyepiece or within the
housing where the observation tubes connect to the microscope body.
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29. SIGNIFICANCE:-
 It is used to identification of minerals in research lab.
 It is used to determined of rock type in the geological work.
 It is used to recognized of crystallization sequence .
 It is useful for mineral exploration.
 Document Deformation History .
 It is used to collect all different optical properties
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 References:-
a. Ore Microscopy by John Wiley
b. Optical Mineralogy by Paul.F.Kerr
c. Olympus Life Science by Internet

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Any Query ?

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