The maesters call it OBSIDIAN.
Game of Thrones Season 2, Episode 8
What the maesters call OBSIDIAN.
Game of Thrones Season 5, Episode 5
Why would OBSIDIAN kill a Walker?
Game of Thrones Season 5, Episode 5
Obsidian. He says you have
a tremendous amount of it here.
Game of Thrones Season 7, Episode 3