Both are sodium chloride as I understand it (but potassium chloride is sometimes used as a substitute for table salt). "Ordinary" table salt is more refined than sea salt, which apparently has lots of trace elements. Non sea salt is mined, but the salt in these mines was originally deposited in ancient oceans anyway. So it is all sea salt. Sea salt is marketed as being brilliant, but possibly contaminated by sea pollutants such a mercury, lubricant and fuel oils.