It is with great sadness I'd like to announce Dr. Hanneman passed away on December 12, 2020. His legacy will live on forever!
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 Post subject: Source of truth for gemstone characteristics? (RI, cleavage)
PostPosted: Tue Jan 07, 2020 10:07 pm 
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Joined: Mon Aug 19, 2019 2:30 am
Posts: 35
I suspect this may be a naive newbie question, but that's what this forum is for, eh? Thanks for your time!

I was looking up information on a gemstone (refractive index and cleavage) and found that the information was slightly different depending on the source I was checking.

The three sources were wikipedia, the gemology project wiki, and the gemology tools professional software.

The RI numbers were fairly close but differed slightly across the 3 sources. Two of the sources listed two planes of perfect cleavage, and one listed it as one plane of perfect and one plane of good.

I guessed that this was due to 1) the natural quality of gemstones (with their unique combinations of elements, impurities, and growth conditions) naturally causes some variance in their characteristics, and 2) some amount of subjectivity in people recording the characteristics (like how people can't agree on what cornflower blue or padparadscha color).

Is that correct? And another reason why gemologists generally shouldn't trust 1 test to be the be-all end-all of identification? :)

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 Post subject: Re: Source of truth for gemstone characteristics? (RI, cleav
PostPosted: Wed Jan 08, 2020 2:44 pm 
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Joined: Sun Oct 16, 2005 12:22 pm
Posts: 20562
Location: San Francisco
There is variance in the refractive index of most minerals.

I always suggest to use the birefringence as an equal or better tool than the listed RIs.
The birefringence is a constant whereas the RI can vary sometimes dramatically.

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