The Glass Dagger appears as a normal dagger with a slight difference in hue. It currently possesses no special properties or uses beyond that of a normal dagger, but this could change in the future. Andrew only appeared for a few weeks, so the daggers are no longer obtainable and are considered a rare.
Worth noting, in Ultima lore, specifically from the single-player Ultima series of games, a glass sword could slay a foe in a single stroke, provided it hit the target, whereupon it shattered making it a single-use weapon reserved for only the most difficult opponents. Glass swords first appeared in Ultima V. It is thought perhaps they will play a similar role in the future of Ultima Online as the Shadowlords extend their influence and control over Sosaria.