Glass sword

The Glass Sword is a one-handed sword, and a very mighty magical weapon, capable of killing every enemy with one, single strike. However, the very nature of this sword is also its greatest disadvantage. After the glass broke, and the magic killed the enemy, the sword is useless and can only be thrown away. Therefore, adventurers keep them for especially dangerous foes. Due to their nature, Glass Swords are light in weight.

According to Vetron's Guide to Weapons and Armour, the Glass Sword has an effectiveness rating of 127. (This is the highest rating listed as the effectiveness of The Black Sword is "unknown". A cannon's rating is only 90)

History
Glass Swords first appeared in Ultima V, in the spot in Serpent's Spine, where in Ultima IV the White Stone was found. Up to six of them the party could posess, but they would only reappear at this very spot after the old swords were being used up.

In Ultima VI, Glass Swords could be found as loot, or were made by a glassmaker in Minoc, who demanded Peer Gems and money for his work. One Glass Sword was needed to make one of the Lenses.

In Ultima VII and VII/2, the Glass Sword was a rare loot. But Pothos in Moonshade sold them too, demanding 1500 Guilders for each sword. The Avatar's Glass Sword was in posession of Hazzard the Trapper.

In Ultima IX, Glass Swords also could be found. But they had lost some power (some enemies survive one strike now)

Trivia

 * In Ultima VI, Glass Swords were useful for destroying doors as well as killing monsters, though sometimes you had to use more than one.