Gems in Growlanser: Wayfarer of Time are the primary source to learn abilities in the game. The gems grant abilities that help raise a character's stats, add a extra hit, increase magic damage, etc.

There are two factors that a player has to consider when equipping a Gem:

The level of the gem: The level of the gem must match or surpass the level of the slot of the Ring for the gem to have effect.

The color of the gem: The color of the gem must match the color of the slot of the Ring, otherwise the AP earned to learn skills cut in half.

See the Rings Section to furter understand the relation between Gems and Rings.