786Shakib Afzal

Semester#7th

Reg#09PWMIN0581

UET Peshawar

19 December, 2012

Dichroscope

Dichroscope

•To identify the gemstone•To inspect ploechroism in gemstones•To separate some common gemstone from each other

Types

Two types

1:Calcite dichroscope2:Polarizing dichroscope

1:Calcite dichroscope

Preferred type used in gemologyUse calcite rhomb to separate

the emerging lightTwo windows appears at the

viewing end

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.

How to overcome this Problem?

Place two polarizing filters close to each other at ‹90⁰

EconomicalResults obtains are less clearStones with weak pleochroism

are hard to determine

Better one?

Calcite dichroscope?Or

Polarizing dichroscope?

Answer isCalcite dichroscope

ok

We will discus the working principles of calcite dichroscope

Proper use and Working principles

1st step:Hold the stone close to the

appertureProvide strong light source

behind the stoneLook through the other end of the

dichroscopeTwo windows will appearExamine the colours in the

windows

2nd stepTurn the dichroscope through

180⁰ keeping the stone in fixed position

Observe the changes in colours again

Possibalities

Three possibalities

1. Colours in both window→unique

Stone→isotropic

2nd

Colours in both windows→two

Stone→uniaxial anisotropic

3rd

Colours in both windows→three

Stone→biaxial anisotropic

The end…

NO!

Any questions?

Then

Thanks a lot

Wish you good luck