What are the differences between sea salt and rock salt?
Realistically? Mostly the price.
The grain structure is likely going to be different too–the rock salt is more likely to have the classic cubical structure, but due to how the sea salt is made, it’s more likely to have a “flaky” or “aggregate” texture. This will affect how the salt tastes if you sprinkle it on prepared food in such a way that the salt doesn’t dissolve before you eat it. (If you stir it into the dish so it does dissolve, you won’t taste the difference.)
There will also likely be minor variations in trace minerals.
Oh, but if you’re thinking about just going down to your local Agway to buy a fifty-pound bag of rock salt to meet your kitchen needs for the next thirty years, don’t–occasionally you’ll find bits of other crud in there. Just get the regular stuff.
I use both kinds of salt, but I find the taste of sea salt or of kosher salt is far superior to that of the regular salt I use.
Regular salt has a bitter, almost metallic taste. Sea salt has a cleaner taste.
The bitter taste you may be experiencing is that of the Iodine added to Iodized salt. More common in Table salt, but Sea Salt can also be Iodized. Usually, most dudes can’t taste it when used for cooking but quite a few can taste it directly.
Otherwise, the two salts taste exactly the same when dissolved, like in a soup.
However, when placed undissolved in the mouth, the two dissolve quite differently, making them “taste” different. More of a “mouth feel” thing, however. In other words, more or less what Hunter Hawk said.
There is a type of very rare sea salt called “Grey Salt” which is greyish with tiny little black specks. Must be harvested under strict conditions, it is also very expensive. Not being pure NaCl it does taste a little different. Clearly it is also not Iodized, even though there can be trace amounts of iodine in this kind of sea salt. This is not the kind of “sea salt” you see on labels of prepared foods.
And to learn more about the fascinating subject that is salt, I recommend the New York Times bestseller Salt: A World History by Mark Kurlansky. More than you ever thought you could know about the only rock we eat.
Often its the crystal size. Here, the most popular sea salt(Alaea) is reddish brown from the clayey soil added.
I often see (and buy) “Pacific Sea Salt”. But why is our beloved Atlantic being left out? Can I buy “Atlantic Sea Salt” or what??
Look, rock salt IS sea salt. It’s just that the sea dried up millions of years ago.
and that sea salt was rock salt before it was washed to the sea.
There’s this pale gray stuff made from seawater called nigari (bitter) in Japanese. It’s made of the minerals occurring in seawater–minus the salt. Mostly magnesium chloride. It’s used to curdle soymilk to make tofu. It’s dissolved in the liquid which is removed in the process, so the tofu does not wind up tasting like it. Because I tried a pinch out of the jar once, and nigari is some of the worst nastiest tasting stuff in the world. So trace amounts of this are part of sea salt and might account for a slight tang. Maybe the gray salt that DrDeth mentioned has a higher proportion of nigari in it, or maybe the gray color is from something else. The pink salt (which they call “hill salt” in Malaysia) is of terrestrial origin and has iron in it, so it’s believed to be good for health.
The cubed shape of rock salt is a result of the maufacturing process
I know that LA BALEINE brand of salt is Mediterranean Sea salt. I think that there may be some French salts that are from the Atlantic.
There is such a thing as food grade rock salt. I have recipes that call for that. Sea salt comes in several varieties and its purity varies. Some of it gets its flavor from other minerals that are allowed to remain with the NaCl so purer is not necessarily better. Kosher salt, that is salt used for koshering meat, at least the kind I use, is pure NaCl. BTW: I don’t kosher meat for the purpose of keeping kosher, I just follow the process in a few recipies like salt crusted beef roast. I use the kosher salt as table salt in salt grinders as I prefer its flavor and texture to iodized table salt.
Flavor variation can be a result of shape as well as mineral content. The fleur de sel that I have tastes yummy, and that seems at least partly due to the shape as it supposed to be fairly low in non-NaCl content.
The part of salt that is actually salt is always the same chemical NaCl. The differences are, as noted above, the shape and size of the crystals, and other stuff mixed up there like anti-caking agents and iodine, or other minerals in the case of some sea salts.
My cooking teacher (a French chef who runs L’Academie de Cuisine in Bethesda, Md.) swears by sea salt, claiming he was skeptical at first but now won’t use anything else.
Food chemist Dr. Robert Wolke wrote a series of articles for the Washington Post in 2000 about salt. The articles are not available for free now but here are some excerpts.
These quotes are just from the preview versions that I could see without paying. I believe the full articles contain more straight dope about myths and truths of sea salt.
Proper rock salt, of course, goes up to 11.
Yeah, heaven forbid anything be put into tofu that might give it some FLAVOR! 
Rock salt is any mined salt, right? Just because the big lumps we spread about in the winter are called rock salt doesn’t mean that non-sea-salt salt isn’t also rock salt? What about the stuff you put into water softeners (if that’s even HCl)? That leaves us with either sea salt or rock salt, if I understand correctly (although as pointed out above, there can be some fibbing).
I always like to bring back sea salt from Cuyutlan if no one minds making the detour from Manzanillo. Cheaper than normal salt here at home, the texture and moisture content makes it a perfect replacement for kosher salt, and it tastes better (or at least the psychological effect is it tastes better).
When working in Ontario I bought something called “large grain salt” or similar wording, because the grocery store didn’t have anything labelled kosher salt; what a mistake. It was hard to control, didn’t dissolved, and everything tasted way the heck too salty. I used it on my driveway at home instead.
For cooking, nothing has beaten kosher salt in my estimation; thanks to Alton Brown for enlightening me of this early on.