Most salt in the United States is sold with iodine added making it iodized salt. (jovinacooksitalian.com)
As rock and sea salt are natural salts, the body instinctively knows how to metabolise them unlike the common table salt (this also includes those with iodine added since it is chemical salt). (novaholisticjournal.com)
Table salt also usually has iodine added because it is crucial mineral that can be difficult to get in your regular diet as well as an additive to keep it from caking. (foodiefriendsfridaydailydish.com)