Please improve this game's materia system

The guessing game that goes along with putting materia into items on this game is starting to drive me nuts.

Each item seems to have it's own unique variances. For example, I destroyed perfectly good materia in an item the other day so I could replace it with a mind materia (the item itself had no mind on it)... only to learn for some weird reason I could not meld Mind materia on it.

This game really needs to do a better job at explaining the materia process and show players what can or can't be melded onto an item. Because the whole system seems very complicated and follows no discernible pattern I can figure. And materia is too expensive and hard to come by to rely on guess-work.