Gem

 could refer to any of the following:
 * Soul Gems
 * Warped Soul Gem
 * Wylandriah's Soul Gem
 * Unusual Gem / Stone of Barenziah
 * Precious stones
 * Amethyst / Flawless Amethyst
 * Diamond / Flawless Diamond
 * Emerald / Flawless Emerald
 * Garnet / Flawless Garnet
 * Ruby / Flawless Ruby
 * Sapphire / Flawless Sapphire

In The Elder Scrolls V: Dragonborn

 * Kagrumez Resonance Gem

Edelstein