The Shadowrite Ore is a block added by Shadowrite. It spawns rarely in the Overworld below y-level 20 in single blocks. It periodically emits whisper sounds audible through walls, and when mined drops a Shadowrite Singularity.
When the first Shadowrite Ore of a world is mined, all players receive the message "The ancient shadows of past horrors have been released!" and Shadowrite Warriors will start to spawn in the world.