Cleaning stone coating- Any ideas?

This looks like a rust stain try a product called CLR its a calcium, lime & rust remover you can find it almost anywhere

Try AWESOME... it works like magic

It looks like it might be rust, from your pic. If it is, try CLR. It removes rust stains, and can be found with the cleaning products in just about every store.

Try mixing some OxyClean and putting that on it. You can put it in wet and then sprinkle some dry on top to form a paste. Keep it wet off and on during the day and then wipe it off. Repeat each day until it is gone.

Have you tried Barkeepers Friend?

What about oven cleaner?

HI Melinda. I believe it will.... You have to keep making the paste and dribbling water onto it off and on for days. Just keep the paste thick. I got a stain out of a granite countertop that way. Before you go to that again, though, you might try CLR. It might be a rust stain. But with stubborn stains like this, it most likely will take repeated applications of most any thing.