Gemology: a "Polariscope"...

[Newbie333]

A second question to the gemologists out there...

Using a "Polariscope"... I know it can be used to detect ''stress and strain'' in a diamond, in order to determine likelyhood of it shattering on the cutting wheel, as well as simply letting a cutter evaluate possible cutting angles, etc...

I wanted to ask how it is different from a ''refractometer''? When would you use this?

Thanks!

-NB333

 

[Hest88]

Look under Study of Gemology here: http://www.yourgemologist.com/

 

[Rhino]

In a nutshell...




The polariscope is a tool used for various reasons but one of it's primary quick tests is to determine doubly refractive stones from singly refractive stones. (Singly refractive stones are gemstones where 1 ray enters and 1 ray exits. Doubly refractive is when 1 ray enters and 2 rays exit).




The speed of light travels at various speeds as it is refracted through gem material moving faster through some and slower in others. A refractometer measures the speed of light through gem material. Taking the measurement is also know as a measuring a gem's "refractive idex". Every gem material has a different refractive index and this test is one of the primary tests used to identify gems properly. A refractometer can, like the polariscope also identify the differences between single and doubly refractive stones except a refractometer will also show you the refractive index of both rays that exit the gem material. FYI diamond is a singly refractive gem and light travels fastest through it giving it one of the highest (if not the highest) refractive index' of any gem.

 

[Garry H (Cut Nut)]

Correction Rhino - light travels at less than 1/2 the speed in diamond as it does in space (2.42 times slower).

 

[Garry H (Cut Nut)]

eg of DR

 

[valeria101]

I was just begging for an opportunity to post that calcite picture, since I hope to move the thing on my desk in the near future... It surely loos like having two culets due to that double refraction. The calcite is listed at Mt. Lily Gems.

PS: Now, where is my high school phisics wrong? is the refractive index a speed? For what I know.... RI = " the speed of light (or any electromagnetic wave) in a vacuum devided by the speed of light in the medium being considered, observable as the degree (angle) to which a transparent material bends light."

 

[Garry H (Cut Nut)]

Correct Val

And the faster ray gets bent more if my memory serves.

And remeber that different colors of the spectrum have differnet speeds (RI's so to speak, but RI is always quoted in sodium orangy yellow light) and that is the cause of dispersion - dirrent refraction bending.

 

[oldminer]

The rays that are slowed down the most are being bent most. Rays that are bent the least are those travelling fastest through the material. At least that's my recollection.