I'll add to what others have said. Having been a
minerals exploration geologist for 10 years, I
think I can add some caution to what has been
said. Vinegar is a weak acid. On some carbonate
bearing rock like dolomite it will not react
without scraping part of the rock into powder.
Dave uses sulfuric acid which is much stronger &
will react without any extra scraping. Geologists
use hydrochloric acid for this purpose. Muriatic
acid can be found at hardware stores. This is an
industrial grade of hydrochloric acid