Here's what I tossed into the wiki jsut then, but thought it'd get seen more (And more importantly, discussed more) here, since it's a rather pivotal part of the game.------------------------------------------------
The crystals may have shattered, but each crystal still had at least one large enough piece to provide a jumpstart to new magic users. The various master crystals were located by the various civilizations, and whole schools of magic have been created around each of the crystals. Most of the crystals are found in heavily guarded areas, as they are obviously a source of power (and in some cases, income) for the particular owner. Other crystals, however, are lodged in secretive societies, either through hoarding of said crystal, or the magic considered an outcast strain of magic by a consensus of modern peoples. When a user who is not familiar with a certain element of magic comes in contact with a new master crystal, their forgotten ability to use magic will be restored. The user is then free to learn this element's abilities along with those he already knew. Beware, however, as most holders of these crystals will charge large amounts of currency for unfamiliar users of their element type.
The other, smaller pieces of crystals are scattered throughout the world, and very useful for the creation of magic-related items or elemental weaponry. Crafters find these useful as they can make better armors weapons, and arrows from them. Magicians and alchemists find them useful to make items that have an amplification effect on their magic.
Smaller still are the void crystals. These crystals were too small to retain a distinct identity, and only hold a small amount of non-elemental energy in them. These can be found nearly anywhere, and are useful for creating one-shot spells that may not be available to someone of another school of magic or a non-magic user. These crystals require mana and a certain level of proficiency in the desired spell before they can be made into a useful spell crystal. Once used, however, the crystal will shatter and no longer be useful. These smaller crystal fragments will, over time, attract enough energy to form another crystal and allow for the magic cycle to continue.
This method would allow for a few things. For one, it would allow a user to select an initial magic type when they are creating their character, or select at a low level. The system, ideally, would also allow for users to participate in any number of classes, magic or not, that they wanted (for a price). The initial school the player chooses will grant them access to all levels of spells free of charge. Should they wish to pick up another form of magic, however, the person would need to pay up to the crystal's owner in exchange for being able to learn abilities of a certain element. Each school would have a tiered system consisting of 3 or 4 levels of spells. The lowest level would have the least powerful spells, but is also the cheapest degree to purchase. The price for a new degree should be quite high to discourage people simply buying their way into all the schools. The time it takes to master any one element should also be considerable, to further discourage people from being able to use all elements, and force them to concentrate on a select few. It may also be useful to only allow a user to have 1 or 2 elements in the first or second learning level, to force them to at least become proficient in said element before moving on to another. And of course, the more powerful or exclusive a crystal's school, the more they will charge, with some demanding more than just currency of a user (or perhaps a certain proficiency in another to prove they are a worthy user of their magic).
The use of perishable crystals would create an economy around magic, as well as allow for these items to be usable for various tasks by melee fighters or crafters (but to a lesser degree than a magic user, since they obviously are not as proficient in magic). The quality (effectiveness) of a crystal could also depend on a chance factor when making it that is dependent on the creators skills in that magic. This would have risk involved in making too powerful of crystals, and make them more expensive to use.