The black salt of India or kala namak, is a salt of volcanic origin, used mainly in the Indian or Pakistani cuisine and is found in the chain of mountains of the Himalayas. It is a very special type of non-refined rock mineral salt with less salting power. Its characteristic gray color (not black) is due to its perfect balance of iron, sulfur and magnesium.
Compared with common salt it has less sodium content which makes it recommendable for all those people who need low-sodium diets. It is rich in hydrogen sulfide which gives it a very particular flavor that could remind us of the fried egg or boiled egg.
Just put bread, oil and salt to extract its peculiar flavor. It can also be used in rice or salads.