Sources. Most unrefined sea salt usually comes from salt mines. It is washed and strained. It is called sea salt as the mines were usually former sea beds. A few brands such as Celtic Salt are harvested from the sea. This is a good product, but products harvested from the sea are much higher in some toxic metals such as mercury that is found in the oceans today, but was not in the oceans as much millions of years ago when the salt beds were formed.