Eye of Ra
A circular crystal approximately five inches in diameter, which creates a weapon of enormous power when used in conjunction with five other crystals (also called "Eyes"). The jewels may serve as a power source and/or a control mechanism, as other Goa'uld technology is also crystal-based.
"Stargate" the Movie - Catherine Langford removes a necklace representing the Eye of Ra from the dig at Giza in 1928, where the Stargate was discovered.
Full Circle - Anubis adds the Eye of Ra to the other crystals he has collected, and obliterates a fleet of System Lord motherships -- then turns the weapon on Abydos.
Fallen - The Eye of Ra is believed destroyed when the power core of Anubis's super-weapon overloads and explodes.