Science Mishap

CoCo has been an avid rock collector for a few years, and my gardens are full of some really interesting and beautiful rocks. As he has gotten older, he has started to try to identify and experiment with some of his rocks. So when he picked up an igneous rock that was loaded with yellow and asked if he could boil it in some water to see what would happen, I said, "Sure!" Well, we boiled, the rock disintegrated into a million pieces, and the yellow was left behind in my pot and on my spoon. Unfortunately, this yellow stuff has adhered itself to my pot and spoon and refuses to budge. I tried reboiling, soap, vinegar, scraping... So, important lesson learned - stone soup needs a special pot reserved strictly for science experiments. It looks like I have one now if anyone needs a loan!(Wish I had taken a picture of the rock. It was too bright for sulfur, and we can't identify it despite lots of research. I'd be thrilled if anyone had any ideas.)