I really love what you did so far with your gems! Their roles are so unique!
Although, I do have a few questions that I'd hope you'd answer.
1. Would you turn every element on the Periodic Table into a gem?
2. What is the highest-ranking gem right beneath and lowest-ranking gem in the entire empire?
Thank you!! I appreciate the complement! I try my best to make all my gems fun and unique.
1. Would you turn every element on the Periodic Table into a gem?
All though most of the elements will be turned into Gems, Not all of them will.
The way I determine whenever a Element is a candidate to become a gem is with one of 2 ways,
The element is a metal or classified as a Geological mineral.
Elements that are Nonmetals are the least likely to become gems as most of them are gases. However Nonmetals that are considered Geological minerals will be. Most of the Elemental Gems are meant to represent the pure form of that element. That isn't to say that The gases wouldn't be represented by a different mineral! for example, Chlorine on its own, wouldn't be a gem, but is represented by Chlorite. same with Fluorine and Fluorite and Carbon and coal.(diamond in theory could count as representing carbon too)
2. What is the highest-ranking gem right beneath and lowest-ranking gem in the entire empire?
In canon, The highest ranking Gems beneath the diamonds is either the garnets or Emeralds. However in my expansion, the Gems that rank right below the diamonds, would be a Cubic zirconia as they help the diamonds oversee their Courts as well as take their place during important events while the diamond take care of other business.
I know this isn't the most original idea, but I like it! it makes Tons of sense to me as Cubic zirconia's are essentially synthetic gems meant to be an alternative to diamonds, and I can have fun designing The different colored zirconia's because there would be more than just White, Yellow, Blue and Pink! (I think I saw this idea originally from @mysticplies so shout out to him!) The Extra colored Zirconia's would be the top of other Departments, so they would rank lower Than the diamond zirconia's.
The lowest ranking Gems would be Rhinestones. (the fake plastic Gems)
Rhinestones are created to give life to decorations. (think wall gem and statue) However when a Gem is sentenced to Being harvested, The rhinestones get replaced by the punished gems.
Most gems don't even acknowledge the fact that Rhinestones exist at all, as they don't considered them to be Gems. all they know is that they could end up as one as punishment. Even the lowest of low gems right above rhinestones in rank, take pride in knowing they aren't Rhinestones.
Rhinestones don't have a set appearance, as they're just created to give life to statues.
Anyway, Thanks for the ask! this one was a fun one because it helps me think more about my gems and the various ideas I can expand upon! Nothing here is 100% and more information about these various gems will come out in the future. Hope I Answered your question!