Black salt, also known as Himalayan black salt, Indian black salt or kala namak, is a volcanic rock salt manufactured in the regions surrounding the Himalayas. It contains, in addition to sodium chloride (the key chemical compound of salt), traces of sulphur compounds naturally found in the Himalayan mountains.
This sulphur content is what gives the salt its unique pungent smell and tangy taste, reminiscent of rotten eggs. Indian black salt can vary in colour - some may not be even black at all. Any shade of brownish pink to dark violet can be found and it is available in whole chunks or in powdered form.