Kala namak or Nalla Uppu is a kiln-fired rock salt used in South Asia with a sulphurous, pungent-smell. It is also known as “Himalayan black salt”, Sulemani namak, bit lobon, kala noon, or pada loon and manufactured from the salts mined in the regions surrounding the Himalayas.
The condiment is composed largely of sodium chloride with several other components lending the salt its colour and smell. The smell is mainly due to its sulfur content. Because of the presence of Greigite (Fe3S4, Iron(II,III) sulfide) in the mineral, it forms brownish pink to dark violet translucent crystals when whole. When ground into a powder, its color ranges from purple to pink.
Kala namak has been praised in Ayurveda and used for its perceived medical qualities.
Kala namak is used extensively in South Asian cuisines of India, Pakistan, Bangladesh and Nepal as a condiment or added to chaats, chutneys, salads, all kinds of fruits, raitas and many other savory Indian snacks. Chaat masala, an Indian spice blend, is dependent upon black salt for its characteristic sulfurous hard-boiled-egg aroma. Those who are not accustomed to black salt often describe the smell as similar to rotten eggs. Kala namak is appreciated by some vegans in dishes that mimic the taste of eggs. It is used, for example, to season tofu or avocado to mimic an egg salad or deviled eggs.
Kala namak is considered a cooling spice in Ayurveda and is used as a laxative and digestive aid.] It is also believed to relieve flatulence and heartburn. It is used in Jammu to cure goitres. This salt is also used to treat hysteria and for making toothpastes by combining it with other mineral and plant ingredients.