fireplace tile

I have ceramic tile on the face of my fireplace, when the tile gets warm it seems to give off an odor. The tile must be glued, I dont see any grout bed between tile and face of fireplace. Smells kind of like a chemical. Could the smell be coming from the glue or tile?

Sounds like Mastic might of been used to install the tile. What was used as the facing to set the tile to?

Its hard to say for sure, as far as I can tell the tile is glued on to the face of the metal fireplace itself. Cant tell if it catches some drywall as wel.