This is a long story but I hope it helps someone else out there. I have been struggling with ugly and embarrassing mineral silica deposits on my fixtures, sinks, and toilets for 25 years, and have finally found something that works to get them off. Our water source is a well, and for years we thought the annoying deposits were from hard water or iron. Despite extensive water treatment with ozonators, softeners, and filtration, the deposits continued. My garage cabinet is full of dozens of various "hard water deposit" chemicals, acids, and scrubbers which did not work. My Kohler kitchen sink looked gross and the finish ruined. A lab re-tested the water and suggested the deposits were likely silica, and could only be removed with razor blades or intense physical scraping, and that replacement would be simpler. Replacing the undermount sink would require replacing the countertops, so we kept looking for solutions. HERE IS WHAT WORKED: Apply "Barkeeper's Friend" powder to a moistened Red scrubbing pad, and use with the cordless drill, and scrub away for awhile. It makes a splattery mess, but the results were actually stunning. The ugly deposits gradually came off, and more importantly the old smooth porcelain finish emerged. What we thought was a lost cause and ruined sink looks almost new again! We wish we had tried this years ago. For some areas smaller pads or brushes are needed, but you can find those, too. It sounds a bit odd, but this is an exciting revelation for our home, as we are going around scrubbing and revitalizing sinks and toilets. I strongly suggest anyone with similar problems give this a try.