Most salt is similar - there is a difference between "sea salt" and "rock salt" but most people wouldn't know in a blind tasting test. "Rock Salt" is just old dried sea bed. There CAN be a slight chemical differences in the proportions of the different mix of chemicals depending on where and how the dry product is manufactured. Sea water is fairly constant in it's proportions of chemicals, but salt made from underground water will vary, from the different proportions of the chemicals dissolved in its path underground.

"Table salt" however has added silica (sand) to keep it dry and free flowing. "Cooking Salt" doesn't, and often absorbs moisture from the air.

Most claims about 'needing' a particular salt are just pretension, or advertising! :-)

But "saltpetre" is a different chemical!

Robin