Blue/Green Materia charges
Green and Blue materia work by creating an effect. The basic effect is a short range ray (25 feet + 5 feet/2 caster levels).
Elemental materia, such as Electric, Cold, and Fire all work this way. Other materia may work differently.
Each usage, or charge, counts towards that materia’s limits per day.
Blue/green materia can be used a number of times equal to your caster level x Materia Level + key attribute bonus (int/wis/cha bonus based on class). So a 4th level caster could use their Novice Water materia in combat around 11-13 times a day (by itself).