I like salt, much to the consternation of my father. But not so much the ordinary iodized, granulated, abrasive stuff that food distributors sell in unrefillable plastic shakers. Rather, I am intrigued - nay, fascinated - by the incredible variety of edible salts that exist. Some among you may say, "For Pete's sake, it's SALT!" And to a point you would be right, but the chemists among us would remark that pretty much any combination of cation and anion can be considered a salt, whether these ions are single atoms or charged molecular fragments. There are some exceptions - please explore. But I like the ones we can eat.
With little exception, the one we can eat and which our bodies require (to a point) is sodium chloride (Na+, Cl-). But rarely in the wild can it be collected in pure form, and hooray for that! Otherwise we would not get pink salt from the Himalayas, grey salt from the Norman coast, pink and yellow salt from Australia, black salt from Cyprus, "black salt" from India, or red salt from Hawai'i, just to name a few... In reality, these are all mostly Sodium Chloride, but either they contain "impurities" in the form of other mineral or salt compounds or they exist in a mixture or matrix with things like charcoal, certain types of dried algae, seaweed, or clay. Any of these additions change the flavour of the salt. Some processed salt is iodized so as to prevent goitres, but rarely does this have much of an effect on taste unless way too much iodine is used.
The other widely variable quality of salts is the texture. Most people are familiar with granulated table salt, rock salt for melting the ice on the stairs, and maybe the superfine variety sometimes used on popcorn. But when salt crystallizes on its own and is then subject to meteorological or geological forces it comes out in amazing shapes (all admittedly based on the cubic crystal structure of NaCl.) Salt from deep underground comes in great big lumps and slabs, solid as the rock it is. Tidal rivers leave thin, wispy crystals along their edges. Salt pools drying in the sun produce the delicate flowers of salt - fleur de sel, and also hollow pyramids that grow upward on their own. And further slow drying produces smaller, crunchy crystals that are fantastic in salads. Each of these textures adds a different something to the dishes to which they're added. Cyprus Flake on a slice of radish, French grey salt on a salad, Hawai'ian red salt as a garnish on sesame noodles or roasted fish.
And I'm not even going to get into the myriad flavoured salts - the most incredibly deadly (in a good way) being black truffle salt. SaltWorks is a good place to get some idea of the global variety.
All of the aforementioned salts exist in the rarefied reaches of the gourmetosphere. Salt as a commodity and ingredient is seemingly commonplace (even if it was not always so - see Mark Kurlansky's Salt.) But as you'll see below, people sometimes bypass the processor/middleman and get their salt directly from the source.
I was recently in The Gambia, where they dearly love their salty food. And not just NaCl, but NaC5H8NO4, otherwise known as MSG. [Aside: when it is used in such prodigious quantities, you can definitely taste MSG...] Leaving MSG aside, since that must be commercially produced by distilling fermented algae, for example, salt in The Gambia can be taken directly from the river Gambia, which is long, flat, tidal, and brackish for more than half the length of the country. The village I stayed in was close enough to the river (and to large salt flats) that raw gathered salt was sold in the daily women's market for the price of roughly 18 cents for a large coffee can full of crystals. Women in the village would sometimes process the salt with iodine but usually would use it raw. And in this case I do mean raw.
The Gambia river is not exactly the cleanest, though there is little, if any, industrial pollution because most industry of any kind happens within about ten miles of the coast. As you go upriver there is little besides fishing villages and one town on an island far upstream. Parasites and bacteria abound, as does very fine silt and some larger particles of plants and plastic. The additional challenge is that often the salt was simply scraped from the top of the salt flats, bringing some of the riverbed with it.
Being the cook, chemist, nerd, salt-lover, and perfectionist that I can be, I decided to purify and refine some of the salt to bring home. In the process of doing so I thoroughly grossed out some of my friends, covered much of the kitchen in super-saturated salt water, and produced a mountain of tiny, fluffy, pale-grey crystals. Here's the process:
Step 1: Get salt. I bought two cans-full of raw river salt from a woman in the market, mostly using gesticulation to communicate. It was grey-yellow-brown and in lumps.
Step 2: Boil, boil, and boil some more. When in doubt of the sterility of something, boil the Dickens out of it. And by Dickens, I mean all of the little creatures that might want to take up an inconvenient and distressing residence in your intestines. And hot water dissolves more salt than cold, which is useful if you're trying to purify a lot of it. Thankfully I found a very large cauldron (though I didn't dance around it...much.) 
Step 3: Skim. Some of the lighter stuff floated to the top in a rather nauseating scummy film that I poured off. However, this still left a really murky brew.Step 4: Make filter apparatus. The kitchen had a tall ceramic teapot (tea being one of the foundations of Gambian social interaction) and I combined this with an old milk-powder can, some Melita paper coffee filters (God only knows why they were there - coffee in West Africa seems to be entirely instant Nescafé), and another funny small filter funnel that didn't seem to have much of a purpose elsewhere. Ultimately, the Melita filters were the most useful and removed the most crud ("crud" being a highly technical term, of course.) I punched some holes in the bottom of the can and used it to hold the paper filters, and then also cut a hole in the can lid to fit the filter funnel. Voilà! A two-stage filter.
Step 5: Filter! I had to pour slowly because both filters would clog and the paper filters would either disintegrate or get crusted with salt after a bit of work.
Step 6: Results. See the difference? (I actually filtered twice.) And see what the filters removed? Degutante!
Step 7: Boil dry. Or almost - it's hard to remove all of the water from a big bunch of salt by boiling. Some of it started climbing over the edge of the pot, too.
Step 8: Bake until fully dry. Baking the pan of salt produced a solid brick since I did not keep it constantly moving to break up the crystal structure as it dried. It also produced some areas of bluish-tinted salt. I found a small handful of these tinted crystals and I have no idea what caused the color. Trace minerals? Any ideas?
Step 9: Powder. I used the back of a spoon and also a wooden pounding mallet to crush the salt into a relatively uniform powder. 
It came out surprisingly light and soft. And then I packed it up - and hoped I didn't get too many questions about the plastic bag of white powdery stuff in my suitcase.Really the most striking difference between this other salt I've eaten is the texture. The taste is slightly different - it does taste a little more like sea water - but the texture is light and fluffy, like powder snow that you can't pack into a snowball because it does not stick. I haven't had a chance to use it much for cooking or eating yet, but I'm excited to do so. And if I get the chance, I'll test it to see what makes it chemically unique.
Who knew Salt could be such an adventure?
