Gem usage

[Flop]

Hi everybody.

I've been playing the game for a little while now, and I'm still trying to figure out what exactly is going on. One thing that I'm still not quite sure about, is how exactly gems are used during combat.

The manual says that a mage can only use one gem to get an increase in the corresponding path. Does this increase last one turn, or the rest of the battle? If it's the entire battle, does the mage take a turn to use the gem, or can he cast spells in the same turn?

I've been avoiding giving my mages gems, since I'm afraid they'll gobble them up, instead of using them for the spells that I script. Will the AI use gems to buff paths when it isn't strictly necessary for casting a given spell?

I'd also be interested in hearing how other people equip their mages gem-wise. Do you give gems to all your mages, or none of them, or maybe just a few select ones?

Thanks in advance.