Orb of the Moons

The Orbs of the Moons are ancient artifacts of unknown origin which allow their bearers to open red moongates by manipulating their placement. They appear in Ultima V,  VI,  VII and  IX as well as in Savage Empire and Martian Dreams. They share some characteristics with moonstones, and are actually referred to as "moonstones" at times.

Age of Enlightenment
For positioning of the Orb in Ultima VI, see: Orb of the Moons Locations An Orb of the Moons first appeared in Ultima V, where such an artifact could be found secreted away in Lord British's Sandalwood Box. Eventually, the Avatar would bring this object to the lost monarch, who would use it to transport both himself and the Avatar's party from out of the great Dungeon Doom, where British had laid imprisoned. Upon his return, the king would then use the Orb to both return the hero to Earth and to exile his corrupt regent, Lord Blackthorn to lands unknown.

Years later, as the Gargish race made its preparations to slaughter the False Prophet, a second Orb of the Moons appeared in the circle of stones behind the Avatar's house on Earth, as part of a trap devised by the gargoyles to ensnare them. After their eventual rescue from the place of sacrifice to which they were drawn, the hero managed to arrive in Castle Britannia, where they would receive explanations as to the use of such Orbs from Lord British, such as they might employ one for expedient travel throughout Britannia. At the end of this particular quest, after the Codex was sent at last to the Ethereal Void, a red moongate appeared heralding the coming of Lord Draxinusom revealed the gargoyle king possessed such an Orb himself.

After the hero's return to Earth following Draxinusom and British's end of hostilities, the Avatar was approached by their friend, Dr. Elliot Archimedes Rafkin, who had heard of the Orb of the Moons and was curious to compare its properties to those of a large meteorite which had recently been discovered in Central America. Experimentation with the meteor revealed that it appeared to be made out of the same substance as the Orb, and a botched test of electrical conductivity opened a warped cubic moongate to the temporally shifted valley of Eodon, where Rafkin and the Avatar would share numerous adventures. Back on Earth, after these events ran their course, the Avatar and Rafkin's associate Dr. Spector, would receive a mysterious package from a red-haired woman purporting to be records of their travels circa 1895, which would instruct the pair as to how to manipulate an Orb of the Moons to produce a gateway in time. 

Age of Armageddon
Years later, in Ultima VII, the Avatar would fail to take the Orb of the Moons to Britannia after being summoned by the Time Lord's red moongate, leading to Lord British lending the hero his own Orb - hoping it would work better for the hero than for him. Disturbances from the Sphere Generator, however, made use of the Orb and the moongates erratic, and gates summoned through the use of the Orb would often repel the Avatar or even injure the hero. The Orb was needed to actually make contact with the Time Lord, as no other way led to the Shrine of Spirituality at that time. With the destruction of the Sphere, all Orbs of the Moons ceased to function altogether, and Draxinusom's personal Orb shattered.

While the hero would not carry Lord British's Orb of the Moons with them in their travel to other worlds, the Avatar was eventually able to obtain a new Orb from the magician Nico, who offered it to the hero in exchange for rescuing him from a ritual sacrifice. In these last days of Britannia, however, the functioning of the Orb had been altered greatly, and it could only be used at the stone circles of the eight gates as a part of the Summon Moongate spell, in conjunction with the invocation of appropriate mantras. That greatly reduced its power and even makes it questionable it's anything like the Orbs of the past spart from the name.

Trinket
An Orb of the Moons came as a trinket with the original boxed release of Ultima VI, and each was unique in shape and any blemishes. Some of the orbs were quite clear, while others were pitch-black. Any blemishes are often white. The material actually is simple glass. As part of the Immortality Contest, however, some boxes contained a runestone in the Orb's stead.

Trivia

 * While it is never mentioned in the games themselves, Richard Garriott indicated that the Orbs of the Moons, as well as the moonstones, are formed out of blackrock in his interview with Caroline Spector for Ultima: The Avatar Adventures.
 * In Runes of Virtue II, the Orb of Moons sits atop the Lycaeum on Verity Isle. From there the hero could travel to any of the eight cities of Britannia.