Blackrock

The mysterious substance known as Blackrock is almost completely indestructible. Only by magical means can it be molded and shaped. Blackrock can be found in small quantities beneath the ground, sometimes near lodes of iron ore or lead. Blackrock is found in Britannia mostly in the dungeon Covetous, although other sources are known as well, such as the Vesper Mines. Blackrock can be excavated by conventional means, but melting it down into a malleable substance is impossible, except by magic.

A combination of electrical energy and magnetic energy has a profound effect upon the substance. Together, these properties cause Blackrock to become permeable, that is, one can put one's hand through the substance as if it were water. Blackrock might work as a teleportation device if magic, electrical energy, magnetic energy, and the correct alignment of heavenly bodies act together upon the substance.

Another property of Blackrock is that it can block the ethereal waves which enable magic. This means that a big enough amount of Blackrock will disable any kind of magic, as long as it is based on ethereal waves.

History
Blackrock was first seen in Ultima VII, where the Guardian's generators and the Black Gate were built of it. Also it is revealed, that Blackrock was found in Britannia more than 20 years ago. Horance's tower in Skara Brae also has Blackrock build into the walls. The Black Sword is also partly made of Blackrock. Blackrock pieces could be mined as well.

In Ultima Underworld II, a Blackrock Dome closed off Castle Britannia. Smaller Blackrock gems were found in the whole game. The three Blackrock Serpents and a huge Serpent statue were seen in Ultima VII/2.

The information about Blackrock in Ultima VII/2 suggests that the material was around in Serpent Isle longer than it was in Britannia; Blackrock existed in the time of the Ophidians.

In Ultima VIII, the Obelisk was made of Blackrock, and the Avatar had to collect the Obelisk Tip, Heart of Earth, Tear of Seas, Breath of Air, and Tongue of Flames -- all Blackrock artifacts -- to recreate the Obelisk to leave Pagan.

Trivia

 * Rudyom's Wand could cause Blackrock to explode.