Heavy piece of stone slab applied over a Stargate when it is buried. The coverstone is designed for much the same purpose as a permanently welded iris, preventing a wormhole from forming when in place.
The Stargate coverstone typically comes in several pieces. One central stone fits into place inside the ring to prevent wormholes from forming. This component frequently has Stargate coordinates inscribed in its center, with the point of origin hidden at the bottom.
Other separate pieces of the coverstone encircle this primary piece and cover the chevrons and inner track.