Cleaning Stained Quartz

When we moved in to our condo in northern Virginia over three years ago from Capitol Hill we essentially had 1,000 square feet in one unit compared to two 500 square foot units. With that came a very large island covered in quartz. It was very shiny and new but didn’t take long to get stained. I know you are supposed to wipe up anything right away to avoid stains. We thought we did that, but next to the sink there was a grungy brownish colored large stain and it was driving me mad - especially since we didn’t know why. So we read up on what it would take to get rid of it. The first attempt was to add even part vinegar and water and rub it. That didn’t do much. So we left the soaked cloth over the area overnight. That didn’t help. So we rubbed it again and left it on again. Maybe a little lighter? The next step was to do equal part baking soda and water. It seemed to work - as I was rubbing the mixture in the brown stain was showing on the white towel. I did it a couple of times and it seemed to make the difference. This mixture also works really well on our stainless steel sink. Then the Weiman daily clean and shine product was sprayed on the whole island and it looked almost new, but the area in question didn’t seem to shine as much. At least the gross stain was removed. It looks so much better. Now we need to do something about the constantly wet grout in the bathroom shower. Based on experience in our Capitol Hill place, it’s not very good.