Black Cube
From Lexicanum
The Black Cubes were ancient weapons of planetary destruction that were used in a war among the first races that inhabited the galaxy. Only five such cubes were known to have been created.
These devices were of Chaotic ritual and required blood sacrifice to activate them. Once started, the process could not be reversed and typically took a day for it to begin its work. It could alter the climate of a planet completely, turning the air into noxious vapours utterly inimical to any form of life, stirring winds to levels that scoured the earth from the bedrock and raised the temperature to the point where oceans would boil; everything on the world, organic and inorganic, would be destroyed.
The Nurthene rebels, the Echvehnurth, possessed one Black Cube which they used against an Imperial expedition during the Great Crusade, some short time before the outbreak of the Horus Heresy. A final offensive was made by the Nurthene against the Imperial forces with their deaths fueling the weapon to activation. This would leave the planet Nurth as a Dead World.
