[Alneyan]

Alchemising gems into gold early on can be a solution, if you *need* that money (if it allows you to build a Mystic for example, or if you need just one more gold coin to build a fort on this turn, and so on). I would probably not use the gems to buy a regular army, unless the situation was truly awful.

On the other hand, fire gems are not necessarily important in the game, as they are of limited use to most nations. Earth gems are likely more useful, and they give less when alchemised to gold, so you will probably not want to alchemise those. I would also stay away from alchemising astral pearls to fire pearls to get more gold, as astral pearls will be of use to all the nations. Even if you are no Astral nation, astral pearls can be converted in gems you need, like Death or Nature.