Margarita salt is a coarse grained salt which is ideal for crusting the rim of a margarita glass. The salty flavor complements the flavors of the margarita, and the light crunch can provide a pleasant mouthfeel. The salt also quickly dissolves once it enters the mouth of a consumer. Many markets sell an assortment of coarse grained salts, all of which are suitable for margaritas, and some shops may sell margarita salt specifically.
Coarse salts are typically sea salts, harvested in large ponds which are slowly evaporated and periodically raked. The evaporation process for coarse salt allows it to form large crystals, which typically have many faces and can be slightly uneven. Some coarse salts are colored, as a result of impurities in the salt water they come from; black to gray salts and pink salts are fairly common. Others are pure white. In addition to being used for margaritas, coarse salts are also used in many kitchens.
To use margarita salt, people typically run a lime around the edge of a margarita glass and then dunk the glass into a container of salt or onto a platter with a thin layer of salt. The margarita is poured into the glass, and then the whole affair is served. As consumers drink, they intake a small amount of salt with each sip; tequila, the primary alcohol in a margarita, pairs very well with salt and lime. It is also perfectly acceptable to serve a margarita without salt, although some purists say that the flavor suffers.
Some salt companies dye their margarita salts. It is possible to find salts in a wide range of colors including green, red, pink, blue, orange, and yellow. Colored salts can be fun and decorative, although the dyes used can cause the salt to taste slightly odd; if you want to use colored margarita salt, you might want to have a taste test to make sure that the dyes don't interfere with the flavor of the drinks.
There are other uses for margarita salt beyond the margarita. Coarse salts are ideal for making salt crusts on things like broiled fish. They can also be added to marinades and pickled foods, and because they do dissolve when cooked, some cooks like to work with a small dish of coarse salt, since it is easy to pinch with the fingers and drop into food. It is also not uncommon to find flavored coarse salts with ingredients like chilies or lavender, for use in salt rubs.