This is all more or less the shadow Im trying to brighten up. I know that representative currency is moderately useless on an international scale, and that real national wealth is instead measured in terms of its commodities and exports. But from what I can see, while Commodities have historically been used for daily trade currency, it is only in developing nations, and eventually they all transition to some minted representative currency. Why is that?
Primarily because Consumables trading is too unstable, at least in non-magical communities, and Commodities are only a little better.
Precious metals are precious because they're rare. Small parts per million/billion in earth's composition. A new gold mine is a boon for a nation, but one isn't going to change the fate of a nation. The value remains because the percentages remain small despite new discoveries. Diamonds, as a commodity, seem to have a lasting value, but that's actually heavily regulated because they've found too many. It's said that they have warehouses of unprocessed diamonds sitting around because they need to control the market.
With your current plan, there's never going to be a shortage of Gems, because everyone can make them. They'd be better than any other commodity or consumable, in that it can be easily and readily replenished. But my concerns about that are...
Well...No and Yes, and a little more no. Im not describing this well. There /is/ a naturally occurring ambient field of energy (though that doesnt really capture its shape very well), and in fact there are 4 of them, each like a different layer (Weather Jetstreams, Ley Line Network, etc; they are simply a natural feature of the World. People CANNOT store energy in themselves, that's fundamental. With the possible exception of some small internal/self-only things the Bloodmages can do (or Plot Items), all workings require an external Power Source. Certain locations have higher concentrations of a given energy; some are epic scale (like a volcano or Niagara-scale waterfall) but most are frontier mundane (a bend in the river with enough flow to turn a Mill-wheel, or the magic energy equivalent). This energy can be tapped by anyone in it's raw form, for example every farmhouse has a bowl of Fire-chits (I need a better name) on the mantle to spark the morning cook fire. It's not a magic trinket or curiosity, it's a simple match and a part of everyday life. It takes skill (and often equipment) to do more complex things with the energy (up to massive complex scientific Circles, done by University Mages), and Power is often sometimes judged by how much energy one can channel at a given time, but every man/woman/child can do enough to release the energy (either raw or channeled into more complex manufactured devices).
I like the idea of any person being able to manufacture these base currencies (given a source like a bonfire or a natural "well" of some kind) because then the presence or lack of a supply chain would be less of an issue, so all regions could reasonably have all/most elements. But that has broader implications on the way labor and effort are valued, which makes me leery.
The alternative would be that while anyone could technically create such things (as in anyone can concentrate energy and fill these containers) but that it is simply not efficient enough on a small scale to be worth the time. The equivalent would be commodity chemicals: in modern times a Nation's Sulfur export is considered one of the better measures of it's overall wealth, and while anyone is capable of distilling sulfur from naturally occurring sources the processes that work on a small (hobby chemist) scale are far less efficient than those on a large/industrial scale, so nobody bothers. In this way it wouldnt be impossible for the landlocked desert folk to have some Water Magic in the village, but it wouldnt be common enough for them to have and use lots of the minted currency. The more I talk about this, the more I think it makes the most sense. It would still mirror a Commodity Currency but it would still be a geographically restricted resource, rather than a pure labor resource (which would encourage some farily despicable slavery motivations). So instead of a family becoming New Money because they found an oil field in texas, they might become rich because they find a new hot spring on the side of their otherwise useless mountain. And on the other end of the spectrum, the hermit in the woods could still charge a container of Fire Magic with a lot of effort and firewood, and in so doing will have enough to stay warm through a snowstorm, but it simply wouldnt generate enough efficiently enough to be a route to wealth.
Honestly, my concern with this is similar to knnn's. If every person can access every Element and make Gems, and the Gems are worth more than they'd make farming or baking or digging ditches or cleaning latrines, then why wouldn't they sit around and make Gems instead? There has to be a limiting factor in why people do what they do.
Religion and obligation is one thing, but it takes true faith to give up wealth readily available should you do something other than your designated part with a lower caste job and lower wages.
As I said before, if it were something I were developing, I'd make it so 100% can use magic, but a smaller percentage, perhaps even as low as 10%, can solidify it into Gems. Those that can make Gems do so, and those that can't do whatever trade they're good at. It could still fit into your religious system, as it will be considered that if you can make Gems, it's your calling and obligation to do so. Families that have generations of Gem-makers would be high class, but would have to walk the line between becoming decadent or superior.
