Blackrock

Blackrock is a mineral noted for its unique properties of magical negation. It appears in Ultima VII, Ultima Underworld II, Ultima VII Part Two, Ultima VII and Ultima IX.

Description
Blackrock can be found in mineral deposits throughout a variety of worlds, and on Britannia it was long harvested near Minoc and Vesper by the Britannian Mining Company. Valued for its ability to deflect ethereal waves, the inert substance was extraordinarily difficult to shape - although certain combinations of magnetic and electrical energy would render it pliable. Magic did not function in the presence of blackrock and those attempting to cast spells around significant deposits would find their incantations either dampened or nullified by the material.

Interestingly, blackrock also appeared to have applications as a medium for inter-dimensional travel, and the substance, when worked on by magical, magnetic and electrical forces in unison could function as a gateway between worlds in conjunction with auspicious planetary alignments.

Historic Uses
Despite its potency as a magical deflector, blackrock featured prominently in a number of mystical constructs. The ancient Ophidians appeared to value the mineral for ceremonial functions and crafted the various ritual serpents needed to open the Wall of Lights out of the substance.

The Guardian's Fellowship made extensive use of blackrock during the early Age of Armageddon, using it to forge the various monolithic generators responsible for disrupting the moongates and ether of Britannia in the years prior to Ultima VII. It also was used in the construction of the trans-dimensional Black Gate through which the Red Titan hoped to enter the realm, in a manner similar to how he had previously used a  blackrock obelisk to enter the world of Pagan. Later, on Serpent Isle, the sage Batlin would also employ a blackrock monolith as a means of travel between realms.Observations on Blackrock

In Ultima Underworld II, the Guardian used his powers to craft a gigantic Blackrock Dome over the entirety of Castle Britannia, a massive magical undertaking which had the fascinating property of creating numerous miniature replicas of the master jewel in several different dimensions - accidentally having triggered the mineral's properties of inter-planar transference alongside its characteristic shielding effect.

The Avatar, themselves, made use of numerous artifacts forged out of blackrock, the most notable being the famed Black Sword, which served as a secure vessel for daemons and other powerful spirits. In addition to this, the hero also made use of various weapons and  armour forged from the material, in addition to encountering numerous artifacts composed of the mineral. In Ultima IX, blackrock armor doesn't bestow magical protection and hinder spellcasting as would be expected.

Ultima VII (SNES)
In the SNES Port of Ultima VII, blackrock is portrayed as a common mineral which is used for decorative purposes by many Britannians. In this version of the game, blackrock may be found in plenty at many Fellowship meeting houses, and is mined openly by the Britannian Mining Company for projects such as Owen's statue.

Trivia

 * Despite Rudyom’s book “Observations of Black Rock” saying that blackrock is absolutely indestructable and can be melted or formed only by magic, the Britannian Mining Company seems able be able to extract it from the ground by more mundane means. Even further, in Ultima IX, Rupert the blacksmith of Trinsic is able to craft a Blackrock sword.