It is a special type of mineral salt with a distinctive / sulphurous flavour.

Black salt or Kala Namak is not black, but more a reddish-grey, because of the presence of trace minerals and iron. It is not interchangeable with pink himalayan salt because of its distinctive flavour.

BLACK HIMALAYAN SALT (Kala Namak) is actually a complex mineral compound with a strong sulphur content. The flavour hits quickly then dissipates to leave a rich mineral salt taste. It is actually a pearly pinkish gray rather than black. Chemically, black salt is sodium chloride, with iron, sulphurous compounds and trace minerals