The Helix Stone is a powerful demonic artifact featured in Doom (2016). It is a large stone with a symbol on it (the same symbol can be found used by the Night Sentinels (holographic knights) and is also found on the armor of the Doom Marine.
SPOILER WARNING: Plot details follow.
Helix Stone is a demonic stone, which the player spot at the end of the level Lazarus Labs. It was first mentioned by Samuel Hayden while the Doom Slayer uses an elevator to go deep into the UAC Base, where he says, that only few had a chance to see it.