A word for a person who looks evaluates jewels for their authenticity and purity

In everyday spoken English, what do you call a person to whom you take your ornaments or jewels and he tells you whether or not the ornaments or the jewel are real, and also how pure the jewel is?

It's not goldsmith that I am looking for. I guess a goldsmith tells you this only about gold and ornaments made of gold, and he makes and sells ornaments made of gold.

But if you were to take a ruby, for instance, to sell or to some shop to just ask them about how pure it was, would you call that evaluator a jeweler? May be you would.

Is there a word that conveys "evaluator of the purity of jewels" and at the same time is in common parlance?

Some more information

A commentator to this question trying to help asks for an example usage so they can help me better.

I am trying to translate a Hindi poem written by a 15th century mystic named Kabir who lived in India.

A few lines of the very short poem can be found here:

https://youtu.be/O5-bpBHvnIA

I am trying to do a better translation than the one done in the video above.

The import of the poem, as it refers to this word, is:

That God, who is the most precious jewel of jewels, and also is the appraisal of all jewels, resides in our own hearts.

And since I am translating a piece of literature, I should probably have said that I am looking for a translation that's common but at the same time not just restricted to the spoken vernacular. It could also be a common usage in popular literature.

I think the more common term is

Gemologist appraiser:

Jewelry and Diamond Appraisals:

Independent Certified Gemologist Appraisers and Certified Gemologist Appraisers of the American Gem Society possess the necessary skills and experience to render valuation reports for your jewelry items. They have been educated in both gemology and the methodologies of jewelry and diamond appraisals