What is organic salt?
It's a comic misnomer, and one I've seen applied recently to a number of fancy salts.
When applied to fruits or vegetables, "organic" means grown without chemical fertilizers or pesticides. When applied to meat, milk or eggs, it means the animal in question ate only organic feed.
When applied to a rock ... I throw up my hands in exasperation.
The salt we eat is a mineral, sodium chloride. It is not grown. It has been in the earth for far longer than we've been on the Earth. Now, some salt is handcrafted, minimally processed, very lovely. That makes it all sorts of things -- artisanal, natural, expensive -- but not organic.
This is not to say that all salt is created equal.
Both table salt and kosher salt are obtained via "solution mining," in which underground salt mines (as in "Back to the salt mines!") are flooded, the water dissolves the salt, and the resultant brine is pumped out and evaporated.
During the evaporation process, table salt is formed into tiny, regular, cubical grains. Anti-caking agents (such as magnesium carbonate or sodium aluminum silicate) are added (so that when it rains, it pours), as well as potassium iodide or potassium iodate. Iodized salt was introduced by Morton Salt in the 1920s, when it was discovered that a diet low in iodine led to goiter, an enlargement of the thyroid. Today, iodized salt guards against iodine deficiency.
Kosher salt is made from the same brine as table salt, but instead of tiny cubes, it is evaporated into larger grains with more surface area. (Each brand of kosher salt has its own proprietary method of forming the grains.) With its comparatively large, flaky grains, kosher salt is easier to pinch up in the fingers, which is one reason chefs prefer it to table salt. And, since an equal measure of kosher salt is less dense (less salty) than table salt, it can be used with less chance of oversalting. (Cook's Illustrated magazine, in its May 2005 issue, worked out the volume equivalents for the two leading brands of kosher salt: For one tablespoon of regular table salt, use 11/2 tablespoons Morton kosher salt or 2 tablespoons Diamond Crystal kosher salt.) Kosher salt contains neither anti-caking agents nor iodine compounds.
Salt connoisseurs eschew solution-mined salt, preferring sea salt or rock salts (among them Himalayan pink salts from Pakistan and Jurassic salt from Utah) that have literally been hewed from rock.
Sea salt is produced by evaporating seawater. Sometimes, the seawater is left in large shallow ponds and is evaporated by the warmth of the sun. Or the seawater may be poured into vessels and heated or boiled. In either case, other minerals in the seawater will remain, lending the salt a distinct look, feel and taste. Popular sea salts include Maldon sea salt from the east coast of Essex in England, Trapani sea salt from the northwest coast of Sicily and, from Long Island's East End, North Fork Sea Salt and Amagansett Sea Salt.
Despite its French name (which means "flower of salt"), fleur de sel is not a regional salt, but a term that describes a production method used the world over: As seawater naturally evaporates in man-made coastal ponds ("salt pans"), fleur de sel is the crust that forms on the surface. It is carefully scraped off, leaving the sel gris (gray salt) to fall to the bottom of the pond.