Magicite

Magicite is a magical substance that can collect, store, and expend magical energy.  It is found in other materials such as crystals, gems, and metals.  It can be extracted and concentrated but is often used as a gem or crystal, or powdered metal. It does not appear naturally in Terria, but Moogles such as Hurdy can get ahold of some, for a price.
An item infused with Magicite can be presented as a reaction to being target by a spell or magic effect that targets only the user and is not an area of effect. The absorbed spell or effect is canceled, and the spell's energy—not the spell itself—is stored in the item. An item has a limited amount of energy it can absorb, depending on the amount of Magicite present, before it is full and can not absorb more. The energy is stored as energy points, one point for each level of the spell canceled or similar for other effects. Once the item has absorbed some energy, the energy can be released to produce spell-like effects depending on the item. Weapons generally expend energy as attack effects, protective items generally expend energy to bolster defenses, etc.
Magicite items must be magical and infusing magicite raises the rarity by one category.
Some maximum energy points:

• ring: 1
• dagger: 4
• shortsword: 6
• longsword: 8
• greatsword: 12
• shield: 20
• breastplate: 12
• half plate: 18
• full plate: 24