[sushiboat]

Only Blood slaves can't be alchemized. Astral pearls are like an exchange currency. Two of another gem kind can be alchemized for one Astral pearl, and two Astral pearls can be alchemized for one gem.

I tend to hoard my gems, but I suppose the best course depends on the situation. You know what spells your research is targeting, so you should have an idea of what the future demand will be. Early expansion is generally considered very important. If the Mystic is primarily for research at the moment, you might consider the danger of having a spell available but being unable to cast it because of a gem shortage.