The distinction between rock salt and sea salt lies in the three areas of origin, composition, and use.
Origin
Rock salt is formed from what remained of inland seas that had evaporated many millions of years ago. Deposits can also be found in estuaries in dry regions around the globe, in landlocked bays, inland marginal seas and around dry lake beds. They are also mined from deep in the earth (1,433 feet) from sedimentary evaporite mineral beds that sometimes are hundreds of meters deep. A typical salt mining company averages 225 million tons available with 3 million tons produced annually.
Sea salt is obtained through evaporation of sea water. It is not processed, or undergoes very little processing. It is done in a high tech version of the method used for centuries. Sea water is collected near the shore in shallow troughs that lead towards the harvesting facility. The water starts off at 3% salinity and gradually increases to 25% where it forms crystals and can be harvested. This process takes a mere five years.
Composition
The composition of rock salt or halite is sodium chloride (NaCl) more commonly known as table salt. In fact it differs from table salt only in the size of its crystals, which are much larger. During formation it forms into isometric crystals.
Sea salt is comprised of sodium chloride and trace levels of minerals like magnesium, potassium and calcium.
Use
Rock salt is also known as “road salt”, so as the name suggests, it is used on roads. It’s unique chemical properties cause ice to melt; therefore, it is an excellent solution for icy roads in winter. However, this solution presents a vicious side effect, rust on vehicles. Rock salt is also used in the making of home made ice cream. When used as a replacement for shotgun shells, rock salt makes an excellent deterrent to trespassers.
Sea salt’s sole usage would be food seasoning. Although relegated to eclectic tastes in the past, recently it has gained increasing popularity for purported health benefits. The benefit of sea salt is said to be reduced sodium, however that is deceptive. The actual amount of sodium is identical. The serving size is smaller because the crystals of sea salt are larger and less will fit in the spoon.
The culprit appears to be iodine. Pamela Peeke M.D., M.P.H., F.A.C.P., nutritionist at Elements Behavior Health and author of The Hunger Fix says “Most table salt has added iodine, an essential nutrient that helps maintain a healthy thyroid but adding iodine can be a problem as well”. So if you eat a healthy diet your iodine level is probably fine as it is already, an excess could lead to nausea, headaches and whacked-out hormone levels. Sea salt, on the other hand, tends to undergo very little processing, leaving behind potentially healthful trace minerals and elements, according to Peeke.