The reaction of marble (calcium carbonate) in a controlled atmosphere containing 10 ppm sulfur dioxide produced calcium sulfite hemihydrate. The sulfite on the reacted samples was converted to a calcium sulfite hydrate in the presence of liquid water. When reacted samples were stored for seven years in a room at normal in-door temperature and humidity (20-25°C and 60-80% relative humidity), no change in the sulfite took place. These observations reveal that moisture in the liquid phase is essential for oxidizing calcium sulfite into gypsum. Marble samples were also exposed to water-saturated environments enriched in nitrogen dioxide. No traces of nitrate were found in any of the exposed specimens, although marbles weathered in a natural environment do contain nitrate.