Gems - GuillermoNigote/Radiant GitHub Wiki

In their native world, the Knights Radiant are able to store the Investiture that grants them access to their powers (Stormlight) in gemstones. If a Radiant right-clicks while sneaking on a diamond or an emerald, they will store part of their Investiture (experience) in it, transforming the gem into its infused version. Performing the same action on an infused gem will return the Investiture to the player.

Villagers will not accept infused emeralds as payment.

Each gem can store a total of 22 experience points. A stack of infused gems is equivalent to 30 levels.