Armor and Weapon Augment Crystals

An augment crystal is a small gem, crystal, or similar object that provides a magical effect when affixed to a weapon or armor.
Each item can hold a single augment crystal, but an attached crystal can be swapped for another one at any time. Attaching an augment crystal to (or removing it from) an item requires a move action that doesn’t provoke attacks of opportunity.
Effectively, each eligible item has a single “slot” that can be filled by any appropriate augment crystal.
Augment crystals are ranked as least, lesser, or greater. (Any crystal without a rank is considered a least augment crystal.) The rank not only describes the relative power level of the crystal’s effect, but also the minimum required quality or enhancement bonus of the weapon for the crystal to function:

• A least augment crystal functions whenever attached to an object of at least masterwork quality, even if the object itself has no magical properties. 
• A lesser augment crystal functions only when attached to an object with a magical enhancement bonus of +1 or higher (such as a +1 longs word or bracers of armor +1).
• A greater augment crystal functions only when attached to an object with a magical enhancement bonus of +3 or higher. Only the item’s actual bonus applies, not its “effective” bonus; for example, a +1 keen holy flaming burst longsword won’t allow a greater augment crystal to function, since its actual bonus is only +1.