Merlin sees the future in the crystal.
Morgana holds the Crystal.
The Crystal of Neahtid is a powerful instrument of magic an an artifact of the Old Religion. According to Gaius, there are many legends about the Crystal. The sorcerers of the past believed it held the secret of time itself. To those who know how to use it, the Crystal holds great knowledge: knowledge of what is, what has been and what is yet to come. It appears in the episode The Witch's Quickening.
The Crystal can only be used by powerful sorcerers, like Merlin and Mordred. The Great Dragon told Merlin that Morgana didn't have the power to wield it, but probably that's because in Series 2 she hadn't mastered her magic.
History
According to the seer Taliesin, the Crystal of Neahtid was hewn from the Crystal Cave (The Crystal Cave). Uther said that many sorcerers died trying to protect it, when he conquered it in the last days of the Great Purge. The powerful warlocks Alvarr and Mordred persauded Morgana Pendragon to steal the Crystal from the vaults beneath the Castle. They would have used it to destroy Camelot and kill Uther. However, Arthur was able to defeat Alvarr and take back the Crystal. It compelled Merlin to look and the young warlock was forced to hold it. He saw a vision of Kilgharrah destroying Camelot. Its whereabouts are now unknown (The Witch's Quickening).
