chocolate disaster

I think my mood transfers itself to my baking. Also I am a terrible chemist. So would a scientific sibling or an experienced baker (mom or rosie, i mean you) please help explain my latest disaster? I was melting chocolate chips on the stove for dipping chocolate balls of death, and the chocolate was a trifle thick - so I added a dab of shortening, thinking that might make it more liquid. Instantly, it turned into solid chocolate putty, the consistency between plado and already-cooked brownies. It was like I added ice-nine. What happened here? WHHHHYYYYYYYYY!