Despite the ghost being out of the ordinary in other ways, it still behaved like one. Castiel didn't feel any cold spots, but the way that it disappeared and reappeared was similar to any other spirit.

No salt and no iron between them. Castiel thought he might have to make an effort to change that in the future. He'd need to start carrying it around like the Winchesters -- what a strange thought.

With no other option open to him, Castiel struck out at the spirit with his blade. It wasn't made of iron, but it was metal, and he could only hope it would disperse it for long enough that they could get away. "Stay back," he hissed at Lust. If this thing decided to do them harm, he'd rather take the damage.