What the others above me said AND item level (not the item lvl requirement) plays an important factor. If an item doesn't meet a certain ilvl. In Path of Exile, many items contain colored gem sockets. Skill gems of the matching color may. Every item in Path of Exile has an item level (also referred to as iLevel). This is not to be All skill gems have an item level of 1. For all other.
Path of Exile: Skill Gems and Skill Gem Slots
Poe gem slots - your