I would assume once the gem is used (however many times or to what extent) that they would shatter or lose power. I think a wave of energy would work, powered by certain emotions. That's a good idea. If you ever read Alice 19th (I sort of doubt due to it being old and hard to find even back then) but it was a short spanning manga that touched upon words having meaning with emotions. Just reminded me of that. We could have Sapphire for Curiosity. Ruby could be Passion. Emerald could be Protectiveness. Etc. And maybe ones used with more malice or ill-intent could sort of..."sour" a gem and make it impure and more damaging in battle? I'd assume if a sapphire is used, it's energy would be blue, either to attack a foe, defend a user, etc. And ruby would have red, etc. I think that's good, others are probably more native to other locations of course, with perhaps others doing the same poking around.