Sangraal
From The Stargate Omnipedia
The Sangraal amulet, worn by MerlinA sacred stone the color of blood, believed to contain great powers. It has also been called the Bloodstone, and the Holy Grail. Merlin wore it around his neck.
King Arthur and his knights departed Camelot in search of the Sangraal, and quested for it in three locations: Castiana, Sahal and Vagonbrei.
The Sangraal was thought to be the source of Merlin's anti-Ori weapon.
KEY EPISODES
Camelot - Kvasir theorizes about how Merlin's weapon works, while SG-1 gains a vital new clue about where to find it.
The Quest, Part 1 - SG-1 discovers the planet where Merlin likely hid the Sangraal, but must get past a series of obstacles set by Morgan Le Fay before they can reach it.