For those of you who haven't seen them yet, look at the pictures from Comet Wild 2. I don't have any details on the constituents of the dust. We may have to wait until the spaceship gets back.
But the pictures are fascinating. Craters, chips, pinnacles .. It looks like something battered and baked. Think how a wad of dirt and ice would look if you cooked it while shooting rocks at it. I look at it and wonder where the pieces that cracked off wound up.