This document discusses dichroscopes, which are used to identify gemstones and observe pleochroism. It describes two main types: the calcite dichroscope and polarizing dichroscope. The calcite dichroscope is preferred as it separates light using a calcite rhomb, allowing two windows that clearly show any color changes when the stone is rotated. The polarizing dichroscope has disadvantages as it can only show one pleochroic color at a time. The document recommends using a calcite dichroscope for better results in determining gemstones with weak pleochroism.

1. 786
Shakib Afzal
Semester#7th
Reg#09PWMIN0581
UET Peshawar
19 December, 2012

2. Dichroscope

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

9. Better one?
 Calcite dichroscope?
Or
 Polarizing dichroscope?

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

16. The end…
Any
questions?

17. Then
Thanks a lot
Wish you good luck