A Doom Shard is a super-powerful energy source.
From the inner chaos of the universe, from here cometh a radiante light, shining brighter than any bejeweled statue that hath ever been imagined. Such radiance, such power, t'ain't possible to hath been controlled by any mortal man. Aye, for many hath been drawn into madness by powers lesser than this. Within it, lieth power enough to destroy us all, and our planet with us... -Extract from the Scripts of Time, on the subject of Doom Shards.
They appear fairly blue-green in pallor, with a strange light shining out from the center. Staring into this light for too long can lead to intense visions, lack of sleep (and/or nightmares), loss of appetite, suicidal thoughts, and usually Demonic Possession.