While inspecting a gas forced-air furnace, I observed a white powder looking material gowing out from the joints on the flue vent. The material looked like a crystal growing, very delicate. Can someone tell me what causes this to grow, what it is, and is it toxic? I have talked with our local gas utility company and they are not much help!
Doug fixed it. 
I just found this yesterday. This seems more like what was originally described. It seems like what was described as a combustion / flue venting issue in the other thread.
Can someone confirm that would be the cause in my image.
