Substance which plays a part in the Ultima CRPGs. It is immutable save by magical means, incredibly dense, and it blocks the passage of magical ether (it is exelent in counter-magics). It has been used in the construction of, magical relays (allowing The Guardian to use his magic within worlds he cannot enter), Weapons (The Black Sword), Magical Prisons (which inhibit the use of magic within), armour, Magical doorways, and even buildings. an attempt by the mage Rudyom of Cove to use blackrock for teleportation resulted in a wand which caused the substance to explode.