Wondrous Item

Rare

As a bonus action, a spellcaster holding the crystal can absorb the mana within the crystal, provided they have access to the type of spell slots. The crystal replenishes 4 levels of spell slots. (Meaning: the sum of the spell slots restored can not go above 4)
If the caster is at their maximum spell slots, the regained slot exists as a temporary spell slot and lasts for 5 minutes before dissipating.   After being used, the Mana Crystal becomes an Empty Mana Crystal (medium), losing its glow and light coloration.

Cost: 250Gp
Weight: 5 lb.