What makes a good sea salt?
All salts (with very few exceptions) can be considered sea salt as they originated from a marine source at some point in time. Their age typically ranges from a few months to millions of years. There are many areas in the world that were once covered by seawater which has been concentrated by drying to form marine evaporites, more commonly known as sea salt. Man has adapted this process to isolate seawater in coastal areas where it concentrates by evaporation with subsequent crystallization of salt. Still others produce sea salt in more controlled environments to try and obtain a product void of natural contaminants.
Good quality, healthful sea salt should contain substantial levels of minerals other than sodium chloride (5-10% or more depending upon moisture content). The major ones being calcium, potassium, and magnesium salts of chloride and sulfate. It should also contain many different minor and trace elements found in natural seawater (at ppm levels or more). Just some include bromide, strontium, copper, zinc, and molybdenum. Sea salts also have varying amounts of moisture in them (1-15% or more) depending upon method of preparation. This can deceive someone into thinking the sodium content is lower than more refined or drier salts.
Natural seawater has a slightly alkaline pH (about 8.3). A good sea salt will typically have a pH somewhat higher (8.5-9.3) due to the formation of carbonates, bicarbonates, and oxides during evaporation. Depending upon the process, some salts can have very high pH's (10 or more). This property is more like that of a caustic or chemical and is not so desirable. Heavy metals are present in all sea salts but good quality ones should contain very low levels (in the sub-ppm range). Some examples include lead, mercury, nickel, and cadmium.
How the sea salt is produced and in what materials also affects salt quality. Is it excavated from ancient sea beds, crystallized in salinas, or dried in evaporators? An accelerated process with intense sunlight and/or heat will likely produce undesirable compounds such as oxyhalides or other unhealthy by-products.
Microplastics, plasticizers, and other extractables from plastics have profound affects on all forms of life and the environment. Is the salt produced, packaged, stored, and transported in healthy materials? Are they plastic, glass, ceramic, cardboard, or natural fiber? A moist sea salt will leach many different chemicals from its container and environment.
Crystal size and shape affects taste, solubility, and visual appeal (coarse, fine, very fine, flake, or flower). Grinding a good sea salt will release some of the fluid inclusions trapped within the crystals. These mineral-rich deposits are easily vaporized and lost in the process, thereby reducing sea salt quality.