Spell Gem (any)

ALPG 2026.2 (page 5):

Unspecified Spell-Storing Items. Non-consumable spell-storing items (e.g. Ring of Spell Storing, Ioun Stone of Reserve, Spell Gems. Enspelled items are “Unavailable Magic Items”) found without specifications must be adapted to a tier-appropriate rarity, empty of spells. During a trade, these items are automatically empty.

An unspecified Spell Gem is rewardable as “empty”.