Today, we will learn minerals and gem identification through Polariscope. There are thousands of gems, rocks and minerals around the world with different characteristics. Scientists have made an observation based analysis about them using different instruments. In fact, instruments are created for analysis of those observations. Observations are collected, analysed and tested.
Let us first tell you what is Polariscope and what is its purpose? and how the test is done?
What is Polariscope?
A polariscope is an instrument in gemology for testing of gems minerals with single refraction, double refraction, Poly-crystalline material or ADR.
The name of Polar - Scope itself shows or describes that a method to see the gemstones from poles or axis through the Scope. It helps in understanding the different colour of light being transmitted by a gemstone. Polariscope basically is an optical device. A polariscope is composed chiefly of a light source and two crossed polarized lenses such as Polaroid {{Registered Trademark}}. One can determine both the optic character and the optic sign of a gemstone. It helps in understanding synthetic, glass or natural gemstones.
In Polariscope, there are two lenses. One is on the top side called " Analyser". The other part is at the bottom which is called " Polariser". Above Polariser, there is " Tint Plate ". Stone is put on the polarizer and analyse through Analyser. Tint Plate plays role in rotation so gems view can be viewed by 360 degrees.
How to Analyse Gems Mineral through Polariscope:-
There is a brief description of two-phase testing methods by polariscope that how gems are tested.
1st Phase of Test:-
Step:1 Rotate the analyser and check if there is complete darkness
Step: 2 Put gem on the polariser
Step: 3 move the gem or rotate the Tint Plate at 360 degrees and note down the light refraction spectrum on gems.
2nd Phase of Test for Further Confirmation:-
Step:1 Rotate the analyse and check if there is complete darkness
Step: 2 Put gem on the polariser
Step: 3 Leave the gem in full light condition
Step: 4 now quickly rotate the analyser only one time and see the final condition of light on a gem.
Type of Identifications of Gems Mineral through Polariscope
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Learn about Dichroscope- The Uses[/caption]
Here is the type of results by which we identify gems minerals.
- SR ( Single Refraction) / isotropic / Cubic crystalline
- DR (Double Refraction) Anisotropic
- ADR (Anomalously double refractive or an
- Anisotropic Aggregate (Polycrystalline)
1- SR ( Single Refraction) / isotropic / Cubic crystalline
Observations:
Stone remains dark through 360 Degree rotation of Tilt Plate. Single Refractive of Isotropic gemstones gives constant dark light. In 2nd phase test, if gemstone appears bright light, it is SR. It occurs in mostly non-crystalline gemstones.
Conclusions
Isotropic - amorphous or cubic
Examples
garnet, spinels, paste, natural glass, flourite, diamond, opal, plastics
2- DR (Double Refraction) Anisotropic
Observations:
Stone becomes light and dark four times through each 360-degree rotation in most orientation. In double refractive, gems mineral give changing light pattern. Sometimes, it appears as dark and sometimes, it appears as light. This happens with mostly in crystalline gemstones.
Conclusions
Anisotropic - uniaxial or biaxial
Examples
Beryl, Chrysoberyl, Corundum, feldspar, peridot, quartz, topaz, tourmaline, zircon, tanzanite
[embed]https://www.youtube.com/watch?v=mNjCT2lTjS0[/embed]
3-ADR (anomalously double Refractive)
Observations:
Stone shows anomalous extinction effect. In this case, the gemstone gives anomalously double refractive. The pattern of the gems gives snake like dark and light both refraction. Smooth snake like refraction occurs mostly in Synthetic or glass stones.
Conclusions
Strain Anisotropy, often in otherwise isotropic material.
Examples
Almandine garnet, diamond, paste, natural glass, verneuil, synthetic spinel, some plastic, amber and some fire opals,
[embed]https://www.youtube.com/watch?v=Ehvq-MZQGNo[/embed]
4-Anisotropic Aggregate (Polycrystalline)
Observations:
In this case, gemstone gives only bright light. Stone stays light through 360-degree rotation in all orientations.
Conclusions
Polycrystalline. Some twinned crystals, some doublets and triplets. Anomalous internal reflection effects.
Examples
Jadite, Nephrite, Chalcedony / Agate, Twinned sapphire, sapphire/synthetic ruby doublet, Reflection from cleavage in flourite.
Polariscope Tutorial by Nick Hodgson of Astrogems
[embed]https://www.youtube.com/watch?v=Co0wJ7YdK0c[/embed]
Learn Gemology online and read these articles also
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