Mirror of Darkness

The Mirror of Darkness is a object that appears in Ultima IX.

Description
The Mirror of Darkness stands in the Guardian's fortress, and is roughly three meters high. It appears to be a spying instrument of the Guardian, as it enables him to see far away places (but not everywhere, as Stonegate was protected from its view by the Time Lord). The Guardian and Lord Blackthorn watched the Avatar's arrival and near-death by dragon fire in it. The mirror later showed the Avatar the destruction of the city Skara Brae at the Guardian's orders. It was destroyed in the end, when the Avatar cast Armageddon, dissolving it into nothing.

The Second Mirror
Confusion arises because a similar mirror can be found in Lord British's bedroom. The mirror is an exact replica. It only shows Armageddon when used, then breaks. The Mirror of Darkness shows it as well, but doesn't break.

Trivia

 * In the original plot, both mirrors had more of a role, as the Guardian used his mirror to send Lord British horrible visions through the other mirror while he's sleeping, in order to set him against the Avatar. Thus why the player gets points when breaking it, since it would end this manipulation. Thus the mirror in the bedroom is an artifact left over from the original plot, as it no longer made any sense in the new plot.
 * Using the mirror in-game (both of the mirrors do) shows the Armageddon video.