Attune Gem( Magic of Faerun, p. 21)
You can magically imbue gems to hold a spell until triggered.
arcane spellcaster level 3rd+, Craft (gemcutting) skill, Intelligence 13+,
You can store an arcane spell in a gem. You must have the spell available to cast (prepared if you must prepare spells; known otherwise) and must provide any material components or focuses the spell requires. If casting the spell would reduce your XP total, you pay the cost upon beginning the attunement in addition to the XP cost for making the attuned gem itself. Likewise, material components are consumed when you begin casting, but focuses are not. (A focus used in attuning a gem can be reused.) The caster level of the spell must be sufficient to cast the spell in question and no higher than your own caster level. A gem can only be attuned with a single spell. The gem must have a minimum value equal to 50 gp per level of the spell to be stored. The base price of an attuned gem (not including the gem's inherent value) is equal to 50 gp per spell level times the caster level. You must spend 1/25 of the base price in XP and use up raw materials costing half this base price. Attunement requires 1 hour plus the spell's normal casting time. The magic gem's market price equals its base price plus its inherent value as a gem. See the Gem Magic section in the previous chapter for the details of attuned gems and gem magic.