As of writing, in the crafting system at least some form of crystal is needed in every recipe. I believe this is similar to FF11. Well when the materia system comes out, maybe remove crystals from normal crafting and make them for creating the various types of materia. So if you need a materia that has plus +2 to attack, vitality, and dexterity, you might use fire, ice, and wind shards. If you want something with a bonus to peity, you could use an earth crystal. And then you could also combine crystals to create certain other types of materia. If you wanted to add water damage to your item you'd make a water materia using water shards and something else.