Dragonshard shields

[yougi]

A friend sent me an adventure he ran, and some NPCs carry Dragonshard Shields. I have no idea what book these are from, nor what they do. Can anyone help me with that?

[Big Fau]

Sharn: City of Towers has a shield enhancement dedicated to House Dennith that are dragonshard-based. I think there's a few similar items scattered throughout the various Eberron splats, but I can't think of any others off the bat.