I'm not sure about expert (most likely just called a professor) but somebody who studies gems is a gemmologist. A mineralogist is linked
gemologist
a person that studies gems is called a gemologist.
mycologist as in : "mycologists have more fungi"
A gemologist studies gems.
One can find natural alexandrite on websites like eBay, Amazon, Gem Society, Khazar Gems, Mark Henry J, Africa Gems, Gem Store, Awesome Gems or AJ's Gems.
What are the similarities between crystals and gems
a person that studies gems is called a gemologist.
When describing them, you could call them precious gems or gemstones.
Expert, Knowledgeable, etc..
A gem collector
The name for a gem expert is a gemologist. They are experts in natural and artificial gems.
You could call them "rocks" or "sparklers."
pullicologist
An expert at table talk is called a deipnosophist.
Horologist
A mathematician.
A language expert is called a linguist. Linguists study the nature of language, its structure, and its use in communication within a specific cultural context.
Horologist