Like fishing, and I assume agriculture, we can have things like "Novia's largest diamond." These would have a greater variance of range than in other harvesting professions, so very large ones could be extremely, extremely rare. They could also vary based on the type of stone. Then, you could have the "largest uncut diamond", versus the "largest cut diamond gem." This would require some masterwork gem cutting skills if you don't want to see the diamond *poof* into fragments, making large cut gems even more rarer. Because, like with fish, the "trophy" versions would have to be different than the "crafting" versions, they would have to be variant types, and this could be tied somehow to the artifact orbs. So, for instance, we currently have a Frozen Tear of the Titans, and the gem version could be a "Titan's Tear Sapphire". A large enough size could even be crafted into an orb by an expert craftsman. A smaller size could perhaps be cut and then incorporated into special jewelry. Also, I previously suggested adding opals to the game. Thread here. The idea was an opal would mix the properties of different gems based on lore like this. My personal wish would be to see that and have normal craftable opals, and perhaps trophy opals, too; rather than opals just being trophies themselves. This would also allow opaline orbs (mixed magic school orbs). If one wanted, I suppose, one should also be able to fragment a "trophy gem" into smaller regular gems, but it would lose its value.
Also, I was just thinking; something interesting might be allowing gem trophies to be cut in many different shapes. Such as... That way, you can get one-of-a-kind pieces of jewelry like this,