Spell Gem

Spell Gems are created by deep gnomes but keep their creation process a secret. A gem can store one spell from any class and released using one action or 1 minute.

Storing
Attuned wielder can imbue the gem with a spell if it's empty, requiring no material components. To do so, a wielder cast the spell while holding the gem. Casting the spell must require either 1 action or 1 minute or longer, and the spell’s level must be no higher than the gems maximum (see the table below). If the spell belongs to the school of abjuration and requires material components that are consumed, the one who stores a spell must provide them, but they can be worth half as much as normal. Once imbued with a spell. the gem can't be imbued again until the next dawn.

Each spell gem has a maximum level for the spell it can store. The spell level determines the gems rarity and the stored spell's saving throw DC and attack bonus, as shown in the Spell Gem table.

Casting
A spell gem can contain one spell from any class's spell list. The holder becomes aware of the spell inside when "learns the gem's properties". While holding the gem, a cater can release the spell from it as an action if they know the spell or if the spell is on their class' spell list. Doing so doesn‘t require any components and doesn't require attunement. The spell then disappears from the gem.

If the spell is of a higher level beyond caster's capabilities, they must make an ability check using their spellcasting ability to determine whether they cast it successfully. The DC equals 10 + the spell's level. On a failed check, the spell disappears from the gem with no effect.

Exandria Unlimited
Opal bought an amber spell gem for 200 gold in Gilmore's Glorious Goods.