I have two smallish (about fist sized) chunks of white quartz that were partly submerged in a forest floor when I found them. I gave them a vigorous scrubbing with dish soap and a stiff brush but there are still dark stains here and there. Can anyone suggest ways to remove the stains? I’m thinking maybe either bleaching with hydrogen peroxide or perhaps a weak acid like vinegar or dilute hydrochloric acid. I’d rather not go with mechanical polishing since I don’t have access to a tumbler.
Not sure if this is the same thing, but this article recommends rubbing alcohol and water for tough stains on a quartz countertop.
" For tough stains that aren’t going away with a little mild dish soap and warm water, try using a surface cleaner and a nonabrasive sponge. Pearson recommends rubbing alcohol and water to create a safe cleanser and stain-remover to get rid of any buildup without having to resort to abrasive cleaners. This method will give that extra kick without risking damage to the quartz surfaces."
HCl is fine, for iron stains, which is likely what those are. And you can use quite strong acids on quartz.
Just be sure it’s quartz, and not calcite…