3. Dichroscope
•To identify the gemstone
•To inspect ploechroism in
gemstones
•To separate some common
gemstone from each other
4. Types
Two types
1:Calcite dichroscope
2:Polarizing dichroscope
5. 1:Calcite dichroscope
Preferred type used in gemology
Use calcite rhomb to separate the
emerging light
Two windows appears at the viewing
end
6. 2:Polarizing dichroscope
Use polarizing filter to observe
ploechroism
Disadvantage:
You can see only one ploechroic
colour at a time.
Difficult to recognize changes in
colour.
7. How to overcome this Problem?
Place two polarizing filters close to each
other at ‹90⁰
8. Dichroscope with two polarizing
filters
Economical
Results obtains are less clear
Stones with weak pleochroism are
hard to determine
10. Answer is
Calcite dichroscope
ok
We will discus the working principles of
calcite dichroscope
11. Proper use and Working principles
1st step:
Hold the stone close to the apperture
Provide strong light source behind the
stone
Look through the other end of the
dichroscope
Two windows will appear
Examine the colours in the windows
12. 2nd step
Turn the dichroscope through 180⁰
keeping the stone in fixed position
Observe the changes in colours again
13. Possibalities
Three possibalities
1. Colours in both window→unique
Stone→isotropic
14. 2nd
Colours in both windows→two
Stone→uniaxial anisotropic
15. 3rd
Colours in both windows→three
Stone→biaxial anisotropic
